UNIT D: ELECTRICAL PRINCIPLES ANDTECHNOLOGIES



Science 9

Unit 4

Electrical Principles and Technologies

Study Guide

Study Guide: This will be your primary study source for the unit.

Text: Science in Action 9 (pages given) or Science Focus 9

Unit Exam Date: TBA

Unit Overview: Electricity provides the means to energize many devices, systems and processes that are part of our technological environment. Electrical devices are used to transfer and transform energy, to provide mechanisms for control and to transmit information in a variety of forms. In this unit, students learn the principles that underlie electrical technologies, by studying the form and function of electrical devices and by investigating ways to transfer, modify, measure, transform and control electrical energy. Using a problem-solving approach, students create and modify circuits to meet a variety of needs. Students also develop skills for evaluating technologies, by comparing alternative designs and by considering their efficiencies, effectiveness and environmental impact.

Focusing Questions: How do we obtain and use electrical energy? What scientific principles are involved? What approaches can we use in selecting, developing and using energy-consuming devices that are efficient and effective in their energy use?

Marking: (approximate)

• Assignments 20%

• Labs/Project 30%

• Quizzes 20%

• Unit Exam 30%

_____

100%

UNIT 4 - Electrical Principles and Technologies Curriculum Overview

A. Investigate and interpret the use of devices to convert various forms of energy to electrical energy, and electrical energy to other forms of energy.

1. identify, describe and interpret examples of mechanical, chemical, thermal (heat) and electrical energy

2. investigate and describe evidence of energy transfer and transformation

3. investigate and evaluate the use of different chemicals, chemical concentrations and designs for electrical storage cells

4. construct, use and evaluate devices for transforming mechanical energy into electrical energy and for transforming electrical energy into mechanical energy modify the design of an electrical device, and observe and evaluate resulting changes

B. Describe technologies for transfer and control of electrical energy.

1. assess the potential danger of electrical devices, by referring to the voltage and current rating (amperage) of the devices. Distinguish between safe and unsafe activities

2. distinguish between static and current electricity, and identify example evidence of each identify electrical conductors and insulators, and compare the resistance of different materials to electric flow

3. use switches and resistors to control electrical flow, and predict the effects of these and other devices in given applications describe, using models, the nature of electrical current; and explain the relationship among current, resistance and voltage measure voltages and amperages in circuits, and calculate resistance using Ohm’s law

4. develop, test and troubleshoot circuit designs for a variety of specific purposes, based on low voltage circuits

5. investigate toys, models and household appliances; and draw circuit diagrams to show the flow of electricity through them

6. identify similarities/differences between microelectronic circuits/circuits in a house

C. Identify and estimate energy inputs and outputs for example devices and systems, and

evaluate the efficiency of energy conversions

1. identify the forms of energy inputs and outputs in a device or system

2. apply appropriate units, measures and devices in determining and describing quantities

of energy transformed by an electrical device

3. apply concepts of conservation of energy and efficiency to the analysis of devices

4. compare energy inputs and outputs of a device, and calculate its efficiency

5. investigate techniques for reducing waste of energy in common household devices

D. Describe the societal and environmental implications of the use of electrical energy

1. identify and evaluate alternative sources of electrical energy, including oil, gas, coal, biomass, wind, waves, solar, nuclear and batteries

2. describe the by-products of electrical generation and their impacts on the environment

3. identify example uses of electrical technologies, and evaluate technologies in terms of benefits and costs

4. identify concerns regarding conservation of energy resources, and evaluate means for improving the sustainability of energy use

1. Identify, describe and interpret examples of mechanical, chemical, thermal (heat) and

electrical energy. (Textbook Pg. 318 – 321)

• What is energy?  The ability to do work or cause change

What are the five main energy tasks?

Energy gives us light.

Energy gives us heat.

Energy makes things move.

Energy makes things grow.

Energy makes technology work.

• There are two types of energy - stored (potential) energy and working (kinetic)

energy.  For example, the food you eat contains chemical energy, and your body stores this as potential energy until you release it (kinetic energy) when you work or play.  Kinetic energy is commonly confused with mechanical energy but they are completely different.

• Energy comes in many different forms, including solar (light), mechanical, chemical, electrical, thermal (heat), and nuclear.

• Radiant (Solar) Energy

• Energy from the Sun

▪ Commonly called light energy

▪ All parts of electromagnetic radiation

▪ Useful forms are light and heat from the Sun

▪ Converted to electrical energy using solar cells

• Mechanical Energy

▪ Puts things in motion such as turbines from turning windmills

▪ Moves cars

▪ Pulls, pushes, twists, turns, and throws

▪ Machines use mechanical energy

▪ Our bodies use mechanical energy

• Chemical Energy

▪ Energy stored in food, wood, coal, petroleum, and other

▪ Energy stored in chemical bonds

▪ Food contains chemical energy that our body needs. Our digestive system breaks up the chemical bonds, releasing the energy.

▪ Photosynthesis in plants – plants take in sunlight, water, nutrients and carbon dioxide.  When these bonds are broken plants produce sugars and oxygen.

▪ Burning wood- fire breaks up chemical bonds, releasing the chemical energy as thermal energy.

• Electrical Energy

▪ The energy of moving electrons

▪ Electric current from a battery

▪ Electrical current from a wall socket

▪ Power plants produce electrical energy

▪ Thermal (Heat) Energy

▪ Energy of moving or vibrating molecules

▪ The faster the molecules move, the hotter the object and the greater the thermal energy

▪ The heat from a fire

▪ Anything that gives off heat has thermal energy

▪ Nuclear Energy

▪ The energy locked in the nucleus of the atom

▪ Bonds between protons

▪ Is released when atoms combine or split

▪ Nuclear power plants split uranium atoms (fission)

▪ The Sun combines atoms to produce helium (fusion)

▪ Debate over whether it is renewable or not

2. Investigate and describe evidence of energy transfer and transformation.

(Textbook Pg 323 – 331, 345-346)

▪ Mechanical energy transformed into electrical energy

o Generators

o While Michael Faraday was experimenting with the first motor, he discovered electromagnetic induction – current can be generated by moving a wire through a magnetic field (or a magnet through a coil of wire). This discovery let to generators that produce a strong and steady supply of electricity to our world today.

o In a hand-held generator, you spin the handle and this spins a coil of wire past magnets. Electricity is induced into the wire and it can be used to power light bulbs, etc.

o In large scale power generating stations, the same principle is used. Massive coils of wire are turned inside of huge magnets. The wire coil is turned by attaching it to the shaft of a turbine (spinning shaft with blades attached). Turbines can be turned by steam, wind or water.

o Motors and generators are very closely related. They use the same mechanisms but are opposite of one another in terms of energy conversion.

Large Power Plant Generator. Small Generator

The electrical energy is then transferred to homes and businesses through a power grid such as the one shown here.

• Electrical energy to magnetic energy

• Electromagnets

• In 1820, Hans Oersted discovered current carrying wires deflect a compass needle by producing a magnetic field. Electromagnets are the result of this discovery. The more wire coils or the stronger the source, the stronger the electromagnetic effect.

• Electromagnets are better than permanent magnets because they can be controlled (shut on and off) and they can be made stronger or weaker.

▪ Electrical energy transformed into mechanical energy

▪ Motor

• In 1831, Faraday made a device that would produce motion using electric current – the first motor.

• Motor parts:

*Source (battery)

*Terminals (where battery attaches to motor

*Brushes (carry current to commutator)

*Commutator (split ring reverses direction of

current flow to armature)

* North and south permanent magnets

attract and repel the armature

*Armature – electromagnets on each end cause

it to spin as it is alternately attracted and repelled by

permanent magnets.

• The spinning armature is attached to a shaft that can turn wheels, fans, etc.

• To make motor stronger, use stronger source, more coils on armature, stronger

permanent magnets.

• To reverse motor direction, change the connections around on the battery terminals or change the direction of the permanent magnets. This is referred to as changing the polarity (direction of current flow).

▪ Thermal energy to electric energy

o Thermocouple

When different metals are subjected to heat on one end and cold on the other, electrons become agitated and move. These moving electrons generate a current in a circuit that is attached to the metal. The greater the difference in temperature, the more current a thermocouple generates. Metals must be different or there is no potential difference (voltage) set up.

o Recovery operations use thermocouples to generate electricity from the heat wasted during incineration of garbage. In this way, some of the wasted energy is recovered.

o Thermocouples can also be used as thermometers. Since the greater the temperature difference the greater the voltage, you can tell the temperature by reading how high the voltage is.

o Thermocouples are used in furnaces to let them know when to shut on and off by reading a current. When a certain current is attained, the furnace shuts off or starts up. In this way, they act as a switch (also called a thermostat).

3. Investigate and evaluate the use of different chemicals, chemical concentrations and

designs for electrical storage cells. (Textbook Pg 288-292)

▪ Chemical energy to electrical energy

o Cells and batteries

o An acid (electrolyte) and base react to create voltage.

o A simple flashlight converts chemical to electrical energy

and then electrical energy to light energy.

• Cells (wet or dry) have two electrodes which are metals of different reactivity (zinc and copper, for example). The greater the difference in reactivity between electrodes, the more voltage the cell creates.

• Cells have an electrolyte which is an ion solution that can conduct electricity. The stronger the electrolyte, the more voltage the cell will produce. The best electrolytes are strong acids (sulfuric acid) but saltwater also works well. The ions (positive and negative atoms) freely move from one electrode to the other and that is how they conduct electricity.

• The electrolyte reacts with the different electrodes in different ways so one becomes positively charged and one negatively charged. When the (+) and (-) metals are connected to a circuit through terminals, current will flow from the (-) to (+) electrode. Placing a load (such as a light bulb) in this circuit will allow the electrical energy to be converted to some other useful form of energy.

• Basic cells like the ones you buy in the store are 1.5 V. More than one cell can be combined to form a battery. Ex. Two 1.5 V cells make a 3V battery.

• Wet cells and dry cells are similar but the electrolyte is liquid in a wet cell and paste in a dry cell. Dry cells are used more for portable, continuous, longer lasting energy while wet cells are more for a powerful initial electrical boost such as the one used to start an automobile.

WET CELL DRY CELL

Direction of current flow

Wire Positive terminal wire

(copper)

Negative terminal Positive terminal

Liquid Electrolyte

Electrolyte Paste

Negative terminal

(zinc) Direction of current flow

• Solar cells or photovoltaic cells (PV cell) offer a limitless and environmentally friendly source of electricity. The solar cell is able to create electricity directly from photons. When photons hit the solar cell, freed electrons (-) move toward one direction leaving a positive charge in the opposite direction. If a circuit is attached, the electrons flow from the negative pole to the positive pole as electrical current. Solar cells may be very large to provide electricity to buildings or they may be very small such as the ones in calculators.

1. Assess the potential danger of electrical devices by referring to the voltage and current

rating (amperage) of the devices. Know what activities are safe and unsafe. (Textbook Pg

284-287)

• A short circuit occurs whenever electricity bypasses the normal pathway in a circuit. When you become that pathway, you are electrocuted.

• Consider voltage and amperage when talking about electrical danger. Amperage is the current that actually flows through your body so high amperage is very dangerous. Voltage is the “pressure” that it is pushed with so although it is dangerous, it doesn’t do the damage that current does. 0.01 A can make your arm go numb and 0.1 A can be fatal. You should be aware of an appliances amperage. For example, computers draw about 0.8 amps while microwave ovens draw 9.0 amps. Therefore, microwaves are a greater electrical hazard than computers even though both are powered by 120 V house wiring. 15 V can give you a nasty shock and 120 V (household voltage) could kill if you are wet. However, it usually takes higher voltage to kill.

• A few hints – jump from a car with a downed power line, don’t step out.

Don’t be the tallest thing around or under the tallest thing around during a lightening storm.

Ground wires (wires leading electricity into the ground and away from where it could do harm) should never be removed.

Don’t bypass safety fuses. If the circuit is supposed to have a 1 A fuse, don’t put a 2 A fuse in instead. The circuit will get too hot and could start a fire. Fuses limit the amount of current that can move through a circuit. If current gets too high, the fuse gets so hot that it melts through, breaking the circuit.

Know how to operate circuit breakers (gray boxes with switches that flip off when a circuit overheats). They are designed to make sure that circuits are not overloaded to the point where they start a fire. For example, let’s say you have a 15 amp circuit breaker. You could add a 7 amp heater and a 3 amp drill. However, if you tried to plug in a 6 amp fan, that would be more than 15 amps so the circuit breaker would flip and your power would be shut off. You would have to unplug one of the devices before it would work.

Avoid frayed wire. Don’t overload a circuit. Unplug appliances before fixing them.

Circuit Breaker Box Fuse

2. Distinguish between static and current electricity, and identify example evidence of

each. (Textbook Pg 275-280)

• Benjamin Franklin experimented with his key and kite to try and discover the electrical properties of lightning. What he captured was static electricity.

• Static electricity is a stationary change that builds to a point where it suddenly discharges. Positively charged particles (missing an electron) attracts negative charged particles (one too many electrons). Lightning is an example, as is static cling. Materials with atoms that are oppositely charged will attract one another while materials with atoms that are the same charge will repel one another. Any charge atom is attracted to an opposite or a neutral charge.

• Current electricity is a steady flow of charged particles through a conductor. It flows until its source is cut off. All of our electrical devices use current electricity, for example, flashlights, and motors. Most of our electricity comes from cells or from electrical generators.

3. Identify electrical conductors and insulators, and compare the resistance of different materials to electric flow. (Textbook Pg 297-301)

| | Examples | Characteristics | Uses |

|Conductor |Metals (copper) |Material that conducts electrical |Used in circuits |

| | |energy (allows current to flow) |to conduct electricity |

|Insulators |Rubber, glass, air |Material that does not allow the flow |Protection from |

| | |of electricity through it. |electrical shock |

|Semi- |Carbon, silicon |Properties of both conductors and |Microchips, |

|conductor | |insulators. |Rheostats |

|Super- |Extremely cold |Almost perfect conductor (almost no |M.R. I.s |

|conductor |metals |resistance to flow) | |

|Resistors |Nichrome and |Conductor that resists the flow of |Light bulbs, heaters, dimmer |

| |Tungsten wire |electricity. It retains the energy |switches |

| | |rather than letting it pass. | |

• Lie detectors work on the principle of resistance and conductivity. When people lie they sweat. Sweat is saltwater which is a good conductor so the machine registers decreased resistance (increased conductivity) when someone is lying.

• How Light Bulbs Work – The electrical current enters the bulb through the hot wire and continues along the circuit to the tungsten filament. Tungsten is more resistant than copper wire so the electricity must work harder to get through. Also, the tungsten is stretched very thin and wound into a tight coil. The small diameter and increased length increases the resistance even more. This means that the tungsten wire gets so hot, that it starts to glow. If it gets too hot, it will break and you will need to replace your bulb.

• How does a toaster work – There are coils inside a toaster of high resistance wire. When the toaster is turned on, the coils heat up because of their increased length due to coiling and their high resistance. The heat is used to toast bread.

4 . Investigate electrical devices and draw circuit diagrams to show the flow of electricity.

(Textbook Pg 311-312)

|Component  | Circuit Symbol  |Function of Component |

|Lamp (lighting) |[pic] or |This symbol is used for a lamp providing illumination, for |

| | |example a light bulb. |

|Motor |[pic] or |A device which converts electrical energy to kinetic energy |

| | |(motion). |

|Fuse |[pic] |A safety device which will 'blow' (melt) if the current |

| | |flowing through it is too high. |

|Fuse |~ |Another symbol sometimes use for a fuse |

|Cell |[pic] |Supplies electrical energy. Single cell (1.5 V) |

|Battery |[pic] |Supplies electrical energy. A battery is more than one cell.|

| | |This one represents an unknown number of cells. |

|Battery | |Another symbol for a battery that defines number of cells. |

| | |This is a 4.5 V battery. |

|Photocell | |A photocell. Light will either turn a circuit with this |

| | |cell on or off. |

|Wire | |To pass current very easily from one part of a circuit to |

| | |another. |

|Voltmeter |[pic] |A voltmeter is used to measure voltage. |

|Ammeter |[pic] |An ammeter is used to measure current. |

|Galvanometer |[pic] |A galvanometer is a very sensitive meter which is used to |

| | |measure tiny currents. |

|Ohmmeter |[pic] |An ohmmeter is used to measure resistance. Most multi-meters|

| | |have an ohmmeter setting. |

|LED |[pic] |A transducer which converts electrical energy to light. |

|Light Emitting Diode | | |

| |[pic] |A resistor restricts the flow of current. |

|Resistor | | |

|Resistor | |Another common symbol used for resistors |

|Variable Resistor | |Used to adjusting lamp brightness, adjusting motor speed, |

| | |and adjusting the rate of flow. |

|Rheostat | |Symbol used specifically for rheostat |

|On-Off Switch |[pic] |An on-off switch allows current to flow only when it is in |

| | |the closed (on) position. |

|2-way Switch |[pic] |A 2-way switch directs the flow of current to one of two |

| | |routes according to its position. |

Circuit diagrams are designed to give everyone

who deals with electrical components a common

and simple language.

5. Use switches and resistors to control electrical flow, and predict the effects of these

and other devices in given applications. (Textbook Pg 302)

• Switch on – metal contacts wire so circuit is complete and electricity flows.

• Switch off – metal does not contact wire so circuit is incomplete - electricity does not flow.

▪ Simple circuit switch

▪ When this switch is closed the light goes

on. When it is open as it is in this picture,

the light stays off. This switch is in the closed position.

• Rheostat is a variable resistor switch

• usually uses resistive wire such as nichrome or semiconductor such as carbon. If current flows through more of the resistor, the light dims because energy is going to the resistor (it heats up). If it goes through less resistor, the light

brightens so you can control brightness. Rheostats can be used to control brightness, volume, speed

(motor) and temperature (heater).

▪ Doorbell switch

This diagram shows an interesting variation of wiring. The 2 doorbell buttons do not have to be right next to each other. One button could be at a front door and the other at a side door. If you follow the circuit, you can see that pressing either button will cause the doorbell to ring. The 2 switches are said to be wired in parallel.

▪ 3-Way Switch

▪ This allows you to turn lights on and off at different locations, for example the top and bottom of stairs.

• A photocell is a device that acts like a switch when it is activated by electromagnetic energy in the form of light waves. Photoelectric cells exist in many types, and are used for many things. It is a type of electric cell whose operation depends upon the extent to which it is exposed to light. The most familiar one is when a door seems to open by itself when we approach it. This happens because our body blocks a beam of light and a photoelectric cell makes the door open. It is also commonly used for security alarms. The photoelectric cell is often referred to as an “electric eye”.

6. Describe, using models, the nature of electrical current and explain the

relationship among current, resistance and voltage. (Textbook Pg 304-306)

Using the flow of water as an analogy can make concepts of electricity easier to understand. The flow of electrons in a circuit is similar to water running through a hose. If you could look into a hose at a given point, you would see that a certain amount of water passes that point each second. The amount of water depends on how much pressure is being applied––how hard the water is being pushed. It also depends on the diameter of the hose. The more forceful the pressure and the larger the diameter of the hose, the more water passes each second. The flow of electrons through a wire depends on the electrical pressure pushing the electrons and on the cross-sectional area of the wire.

Voltage

The pressure that pushes electrons in an electrical circuit is called voltage.

Using the water analogy, if a tank of water were suspended one meter above the ground with a one-centimeter pipe coming out of the bottom, the water pressure would be similar to the force of a shower. If the same water tank were suspended 10 meters above the ground, the force of the water would be much greater, possibly enough to hurt you. (If you jumped from a one-meter diving board, the force when you hit the water would not be too great. If you jumped from a 10-meter board, the force would be much greater.) Voltage (V) is a measure of pressure, or electromotive force, applied to electrons to make them move.

It is a measure of the strength of the electric current in a circuit. Voltage is measured in volts (V). A volt is the amount of electromotive force (emf) needed to push a current of one ampere through a resistance of one ohm. This definition will make more sense after you learn about current and resistance. Just as the 10-meter tank applies greater pressure than the 1-meter tank, a 10-volt power supply (such as a battery) would apply greater electromotive force than a 1-volt power supply. Voltage potential is the electrical term that is analogous to water pressure. AA batteries are 1.5-volt; they apply a small amount of voltage or pressure for lighting small flashlight bulbs. A car usually has a 12-volt battery––it applies more voltage to push current through circuits to operate the radio or defroster. The standard voltage of wall outlets is 120 volts––a potentially dangerous amount of voltage. An electric clothes dryer is usually wired at 240 volts––a very dangerous amount of voltage.

Current

The flow of electrons can be compared to the flow of molecules of water. The water current is the number of molecules flowing past a fixed point; electrical current is the number of electrons flowing past a fixed point. Electrical current is defined as electrons flowing between two points having a difference in voltage potential. Current is measured in amperes or amps (A). One ampere is 6.25 x 1018 electrons per second passing through a circuit. With water, as the diameter of the pipe increases, so does the amount of water that can flow through it. With electricity, a conducting wire is the pipe. As the cross-sectional area of the wire increases, so does the amount of electric current (number of electrons) that can flow through it.

Resistance

Resistance is a property that slows the flow of electrons––the current. Using the water analogy, resistance is an impediment to water flow. It could be a smaller pipe or fins on the inside of a pipe. In electrical terms, the resistance of a conducting wire is dependent on the metal used to make the wire, and the diameter of the wire. Copper, aluminum, and silver––common metals used in conducting wires––all have different resistance properties. Resistance is a characteristic property of a conducting material. Resistance is measured in units called ohms Ω). There are electrical devices, called resistors, designed with specific resistance that can be placed in circuits to reduce or control the flow of the current. Every electrical appliance contributes resistance to a circuit, as well. Any appliance or device placed within a circuit to do work is called a load. The light bulb in a flashlight is a

load. A television plugged into a wall outlet is a load. Every load introduces

resistance in a circuit.

Ohm’s Law

George Ohm, a German physicist, made an important discovery about electricity in the early 19th century. He found that in many materials, especially metals, the current that flows through a material is proportional to the voltage across the material. In the substances he tested, he found that if he doubled the voltage (V), the current (A) also doubled. If he reduced the voltage by half, the current dropped by half. The resistance (Ω) of the material remained the same whether the voltage and current increased or decreased. This relationship is called Ohm’s Law, and can be written in three simple formulas. If you know any two of the measurements, you can calculate the third using these

formulas:

7. Measure voltages and amperages in circuits, and calculate resistance using Ohm’ Law.

(Textbook Pg 306-308)

|Current (I) is |Measures amount of electrical current. |Measure using an ammeter (measures |

|measured in |Most household devices have low amperage (i.e. a |exact current) or a galvanometer |

|Amps (A) |kettle uses 13 A). |(measures very low currents). Galvanometers can be made |

| | |from |

| | |a wire and compass. |

|Voltage is |Measure of how much |Measure using a voltmeter. Measure |

|measured in |Electrical energy each charged |the potential difference in amount of electrical energy |

|Volts (V) |Particle has. The higher the |from one point to |

| |Voltage, the greater the |another. Digital or analogue (read scale very |

| |Potential Difference. |carefully!). |

| |Household voltage 120 V, | |

| |Cells 1.5 V. | |

|Resistance is measured|Measures how difficult it is for electricity to flow. |Measure using an ohmmeter. |

|in |Nichrome wire |To calculate, R = V/I. For example, if |

|Ohms (Ω) |has very high resistance so it is |you have a 3 Volt battery and a 6 amp |

| |difficult for current to pass. Copper |bulb in a circuit, resistance would be |

| |wire has very low resistance so |R = 3/6 = 0.5 ohms. The greater the resistance, the more |

| |current flows easily. |heat you have. |

Multimeters can be used to measure all three properties with one instrument.

Ammeter for current Voltmeter for voltage

Hand made galvanometer to measure Multi-meter measures

small amounts of current current, voltage and resistance

Parallel and Series Circuits (Textbook Pg. 311 – 315)

There are two ways of connecting components:

In series so that each component has the same current. The battery voltage is divided between the two lamps. Each lamp will have half the battery voltage if the lamps are identical.

| |In parallel so that each component has the same voltage. Both lamps have the full battery voltage across them. The battery |

| |current is divided between the two lamps. |

| | |

| | Series Parallel |

▪ The terms series circuit and parallel circuit are sometimes used, but only the simplest of circuits are entirely one type or the other. It is better to refer to specific components and say they are connected in series or connected in parallel.

If several lamps are connected in series they will all be switched on and off together by a switch connected anywhere in the circuit. The supply voltage is divided equally between the lamps (assuming they are all identical). If one lamp blows, all the lamps will go out because the circuit is broken.

If several lamps are connected in parallel each one has the full supply voltage across it. The lamps may be switched on and off independently by connecting a switch in series with each lamp as shown in the circuit diagram. This arrangement is used to control the lamps in buildings.

| |Example |Description |Adding loads |Removing loads |Adding cells |Advantages |Disadvantages |

|SERIES |Flashlight |Current passes |Each added load|When one load |Cells added in |Simple to |Circuit all goes |

| | |through each |means less |burns out, others|series result in |construct |off if one load |

| |Switches in |load in turn so|voltage for |all go out since |added voltage | |burns out |

| |homes |voltage is |others so |circuit is broken|(i.e. two 1.5 V |Uses less energy | |

| | |shared |lights dim | |cells add up to 3V| | |

| | | | | |battery | | |

|PARALLEL |Household |Separate |No difference |Other loads stay |Cells added in |Flexibility in |More complex to |

| |wiring |current for |since all loads|on since they |parallel do not |operating loads |construct |

| | |each path so |get full amount|have a separate |increase voltage |together or | |

| |Most tree |each load gets |of voltage |conductor back to|but they do make |separately |Use more energy |

| |lights |a full share of| |source |each cell last | | |

| | |voltage | | |longer | | |

8. Identify similarities and differences between microelectronic circuits and circuits in a

house. (Textbook Pg 315)

• Resistors of various values (i.e. 0.1Ω to 200Ω ) are used in electronics. They are used to control how much current is allowed to flow to each component in a complex circuit. Microcircuits have very low resistance and amperage compared to regular circuits.

• Transistors are used as switches in tiny microcircuits. They can stop or start current in several different directions at once. They basically do the same thing as switches in larger circuits.

Transistor Resistor Motherboard

1. Identify the forms of energy inputs and outputs in a device or system. (Textbook Pg 321)

• Electrical – potential energy of charged particles released when they flow or discharge (i.e. generator).

• Mechanical - energy of moving objects or potential energy of objects that could move

(i.e. rock on edge of cliff).

• Thermal – energy of vibrating particles in a substance. The faster the particles move, the more heat energy produced (i.e. hot water).

• Chemical – potential energy stored in chemicals and released when there is a chemical reaction (i.e. battery).

• Some common energy conversions include:

|Input energy |Output energy |Device |

|Mechanical |Electrical |Generator |

|Chemical |Electrical |Cell or battery |

|Electrical |Mechanical |Motor |

|Chemical |Electrical to thermal |Light bulb |

|Thermal |Electrical |Thermocouple* |

|Electrical |Thermal |Oven |

|Chemical |Mechanical |Digestion |

|Light |Electrical |Photocell |

Input energy is what you start with, while output energy is the end result.

A transformer is an electrical device that takes electricity of one voltage (usually very high voltage power lines) and changes it into another voltage (usually lower voltage house current). You'll see transformers at the top of utility poles, in the green boxes in neighbourhoods and even changing the voltage in a toy train set.

2. Apply appropriate units, measures and devices in determining and describing quantities of

energy transformed by an electrical device. (Textbook Pg 332-333)

Electrical Power

Power is a measure of the rate of doing work or the rate at which energy is converted. Electrical power is the rate at which electricity is produced or consumed. Using the water analogy, electric power is the combination of the water pressure (voltage) and the rate of flow (current) that results in the ability to do work. A large pipe carries more water (current) than a small pipe. Water at a height of 10 meters has much greater force (voltage potential) than water at a height of one meter. The power of water flowing

through a 1-centimeter pipe from a height of one meter is much less than water through a 10-centimeter pipe from a height of 10 meters.

Electrical power is defined as the amount of electric current flowing due to an applied voltage. It is the amount of electricity required to start a device or operate a load for one second. Electrical power is measured in watts (W). The formula for power that quantifies this relationship is:

Measuring electrical power can be confusing because a watt does not sound like a rate. Usually we think of rates as ratios––miles per hour or miles per gallon. A watt is, in fact, a ratio; you must learn about another measurement to understand it––a joule. A joule is a measurement of work performed. One watt is the rate of doing work when one joule of energy is used in one second (1 watt = 1 joule/second).

A 50–watt light bulb uses electrical power at a rate of 50 joules per second. A 100---watt light bulb uses electrical power at the rate of 100 joules per second.

For example, you are using a drill that draws 12 amps from a 6 volt battery.

How much power is consumed by this drill?

P = I x V

= 12 x 6

= 72 watts

A kilowatt hour is a measure of power. It is just a larger unit for measuring large amount of electrical power use such as at your house.

Energy

• E = P x t Energy is the ability to do work.

Energy = Power x Time

For example, you turn on a 100 watt bulb in your bedroom and leave it on for one hour. How much energy did you consume?

E = P x t

= 100 x 3600 (remember to convert 1 hour to seconds by multiplying by 3600)

= 360 000 joules (or 360 kJ or 0.36 MJ) MJ = megajoule kJ = kilojoule

When you are dealing with watts or joules, the unit of time is always seconds. You often need to convert minutes (x60) or hours (x 3600) to seconds when doing problems.

3. Apply the concepts of conservation of energy and efficiency to the analysis of energy

devices (light bulbs). (Textbook Pg 338)

• Some devices are more efficient than others. Incandescent bulbs are only 5% efficient, meaning 5 joules of light are produced. The rest of the energy doesn’t just disappear. It can’t, according to the law of conservation of energy. The other 95 joules is converted to unwanted heat. Fluorescent bulbs are 20% efficient.

4. Compare energy inputs and outputs of a device and calculate its efficiency. (Textbook Pg 335-336)

• Ef = Eo / Ei x 100

Efficiency = Energy output / Energy Input

% = joules/joules

For example, you are using a gasoline powered trimmer on the grass. You will need to add 2100 joules of energy from the gasoline in order to get 700 joules of useful work from the trimmer. What is the efficiency of the gas trimmer?

Ef = Eo / Ei x 100

Ef = 700 / 2100 x 100

Ef = 33.3 x 100

Ef = 33%

The smaller the number, the less efficient the device will be. No machine is 100% efficient. There is always some energy wasted through heat loss, sound, motion, etc. For example, if a hair dryer used 140 J of electrical energy and was able to produce 20 J of usable energy in the form of mechanical (fan) and heat, the efficiency of the hair dryer would be [(20 ÷ 140) x 100 = 14% efficiency].

5. Investigate and describe techniques for reducing waste of energy in common household

devices. (Textbook Pg 339-342)

• There are lots of things that people can do to reduce energy waste. For example:

o Make sure that moving mechanisms are well-lubricated to reduce friction.

o Use more efficient types of light bulbs (energy efficient fluorescent or halogen bulbs)

o Don’t over dry clothes

o Don’t use an entire wash cycle for a pair of socks

o Turn off the lights!

• Energuide labels help us increase efficiency by showing us which devices are the most efficient before purchasing them. The label tells the average number of kWh it would use in a year and compare its efficiency on a scale with other models. Most efficient appliances have insulation that keeps warmth or cold in so that electricity is conserved.

• Reducing friction, using more insulation, etc. are ways of making energy more efficient. You can reduce friction by using ball bearings, lubricants or fewer moving parts.

1. Identify and evaluate alternative sources of electrical energy, including oil, gas, coal,

biomass, wind, waves, solar and batteries. (Textbook Pg 345-350)

|Source |Advantages |Disadvantages |

|Fossil fuels (coal, oil, natural gas). Most of|Relatively cheap, technology is already|Non-renewable, pollution from burning fossil fuels is|

|Alberta’s energy is from burning coal. The |in place. |dangerous for the environment. |

|fire heats steam that then turns a generator | | |

|turbine. | | |

|Wind. The wind turns blades on a windmill that|Renewable ,clean |Location - limited |

|are attached to a turbine on an electrical | | |

|generator. | | |

|Waves/Tides. Turbines attached to generators |Renewable, clean |Location - limited |

|are placed offshore and turn when tides come in| | |

|and out twice a day. | | |

|Biomass. Trees, agricultural waste, manure, |Renewable resource. |The burning does produce some sulfur dioxide and |

|sewage, scrap wood from construction, etc. This| |nitrogen oxide (acid rain) but far less than fossil |

|is burned and the fire heads steam that then | |fuels. |

|turns a generator turbine. | | |

|Battery-powered cars. These would be lead-acid|Wouldn’t have the pollution from |Nonrenewable. Cars will be heavier, slower and won’t|

|batteries. |burning fossil fuel. |go as far as regular cars because of the weight of |

| | |the battery. The lead-acid batteries will release |

|(This idea has pretty much been abandoned by | |toxic lead into the environment and making the |

|car manufacturers) | |batteries would create industrial waste. |

|Fuel Cell powered cars. Cars would carry |Renewable. Twice as efficient as |Hydrogen can be dangerous if not handled properly. |

|compressed hydrogen gas that would mix with |fossil fuels. Quiet – no internal |Auto manufactures are still perfecting the design but|

|oxygen in a chemical reaction that produces |combustion engine. The only waste |the first cars should be out very soon. |

|water. Energy released turns a motor which |product is water. | |

|turns axles on car. | | |

|Solar. Solar panels convert thermal energy to |Renewable, clean. |Location is limited. Expensive. Takes up lots of |

|electrical energy. | |space. |

2. Describe the by-products of electrical generation and their impacts on the

environment. (Textbook Pg 351-353)

• Most electricity in Alberta is generated from burning coal. Byproducts include:

o Sulfur dioxide – combines with water in the air to produce sulfuric acid, causing acid rain.

o Nitrogen oxide – combines with water in the air to produce nitric acid, causing acid rain.

o Carbon dioxide – a byproduct of any burning, CO2 is a greenhouse gas and is causing our Earth to warm excessively.

o Fly ash (very fine particulate) contains mercury and arsenic. These toxins then settle into water systems where they become more concentrated.

3. Identify example uses of electrical technologies and evaluate technologies in terms of

benefits and impacts. (Textbook Pg 354-358)

• Used for heat, light, movement, communication

• Binary system – electrical systems communicate using two numbers – 0 and 1. Basically, 0 is off and 1 is on. The microcircuits in the electrical system are told to turn on and off in order to create a code that can be translated into usable information.

• One of the most recent technologies has been in the field of communication. Computers, and especially the internet have allowed us to become a single, global community.

• Benefits – better understanding of the world, ability to do business without having to travel great distances, saves time, opens up a world of information that was not available before

• Drawbacks – your personal information, including financial information, is easily available to those who know how to get it, you are never really sure who you are “talking” to, you don’t know if the information you read is accurate or not, your personal computer can be attacked by viruses that wipe out important information that you have saved, prosperous countries are at an advantage

4. Identify concerns regarding conservation of energy resources, and evaluate means for

improving the sustainability of energy use. (Textbook Pg 350)

• Most of our energy is produced through non-renewable resources (fossil fuels). Once these are used up, we will no longer be able to produce energy the way that we now do.

• Finding alternative energy sources can be very expensive and if you live in the wrong place, it can be almost impassible. Also, it will take a tremendous amount of time to convert our society from fossil fuel consumption to other forms of energy.

• In order to make our energy last as long as possible, it will be important to conserve by not wasting as much as we do. We can also find sustainable ways to use our resources. This means that we use some, but we have a plan in mind that will make sure the resources will also be available for future generations. For example, selective logging uses the old trees but does not cut down the young ones. In that way, they will be ready in years to come. Some coal burning operations are mixing biomass in so that the coal will be there in the future if we still haven’t converted to another source.

1. Ask questions about the relationships between and among observable variables, and plan

investigations to address those questions.

• Rephrase questions in a testable form. For example, instead of “Why do we use parallel circuits rather than series circuits in household wiring?” a testable questions would be “How do series circuits and parallel circuits respond differently under load?”

• Predict the amount of current in a circuit of known resistance and applied voltage (as voltage increases, so will current).

• Provide operational definitions (concrete, measurable) for current, resistance, voltage and polarity (direction of current flow).

2. Conduct investigations into the relationships between and among observations, and

gather and record qualitative and quantitative data.

• Estimate the efficiency of a mechanical device based on how much heat it produces.

• Use ammeters and voltmeters to make accurate measurements.

3. Analyze qualitative and quantitative data, and develop and assess possible explanations.

• Evaluate the safety, durability, efficiency and environmental impact of a personally-constructed wet cell design.

• Measure the current in similar circuits, and provide possible explanations for differences in current flow (series versus parallel).

4. Work collaboratively on problems and use appropriate language and formats to communicate ideas, procedures and results.

• Use charts to present data on the voltage, current (amperage) and resistance found in series and parallel circuits).

-----------------------

Topic A: Investigate and interpret the use of devices to convert various

forms of energy to electrical energy, and electrical energy to

other forms of energy.

V

Zn Cu

Electrodes

V

Topic B: Describe technologies for transfer and control of electrical energy.

+

-

+

+

Push doorbell in

On

Off

Switch

G

G

Circuit Diagram

Symbols for Cells:

Series

Parallel

Cells in Series

Cells in Parallel

Topic C: Identify and estimate energy inputs and outputs for example devices

and systems, and evaluate the efficiency of energy conversions.

Topic D: Describe and discuss the societal and environmental implications of

the use of electrical energy.

SKILLS TO KNOW

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