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PHYSICS 2019-20February 19, 2020Today’s Agenda (Day 109)HOUSEKEEPINGHomework Check Chapter 23 Vocabulary Chapter 23 NotesClass Activity CONT’D LABS: 1) Light that Bulb; 2) Observing Magnetic Strength and Fields CONT’D: Chapter 23 Section 23.3 - Application of CircuitsHOMEWORK:Read Chapter 23 – Series and Parallel CircuitsStudy for Chapter 23 TestChapter 24Polarized Magnetic fieldSolenoidGalvanometerArmatureDomainMagnetic fluxElectromagnetElectric motorChapter 25Electromagnetic inductionElectric generatorEddy currentTransformerStep-up transformerInduced electromotive forceLenz’s lawSelf-inductanceMutual inductanceStep-down transformerREMINDERS:Chapter 23 Test February 18 February 20Lab Reports: Light Bulb & Magnetic Strength – February 21; 11:59:59 pmChapter 24 Vocabulary – Feb 19Chapter 24 Notes – Feb 21Chapter 24 Test February 25Chapter 24 & 25 Quiz February 27Chapter 25 Test March 3PHYSICS 2019-20Practice ProblemsCH 23 PRACTICE PROBLEMSSECTION 23.1Three 22 Ω resistors are connected in series across a 125 V generator. What is the equivalent resistance of the circuit? What is the current in the circuit?A 12 Ω, a 15 Ω and a 5 Ω resistor are connected in a series circuit with a 75 V battery. What is the equivalent resistance of the circuit? What is the current in the circuit?A string of lights has ten identical bulbs with equal resistances connected in a series. When the string of lights is connected to a 117 V outlet, the current through the bulbs is 0.06 A. What is the resistance of each bulb?A 9V battery is in a circuit with three resistors connected in series.If the resistance of one of the resistors increases, how will the equivalent resistance change?What will happen to the current?Will there be any change in the battery voltage?Suppose the circuit shown in Example Problem #1, p. 628, has these values: R1 = 255Ω, R2 = 290Ω, and V1 = 17V. No other information is available.What is the current in the circuit?What is the potential difference across the battery?What is the total power used in circuit, and what is the power used in each resistor?Does the sum of the power used in each resistor in the circuit equal the total power used in the circuit? Explain.Holiday lights often are connected in series and use special lamps that short out when the voltage across a lamp increases to the line voltage. Explain why. Also explain why these light sets might blow their fuses after many bulbs have failed.A 22 Ω resistor and a 33 Ω resistor are connected in series and are connected to a 120 V power source.What is the equivalent resistance of the circuit?What is the current in the circuit?What is the potential difference across each resistor?You connect three 15.0 Ω resistors in parallel across a 30.0 V battery.What is the equivalent resistance of the parallel circuit?What is the current through the entire circuit?What is the current through each branch of the circuit?Suppose you replace one of the 15.0 Ω resistors in the previous problem with a 10.0 Ω resistor.How does the equivalent resistance change?How does the current through the entire circuit change?How does the current through one of the 15.0 Ω resistors change?Compare and contrast the voltages and the currents in series and parallel circuits.A?parallel?circuit?has?four?branch?currents:?120?mA,?250?mA,?380?mA,?and?2.1?A.?How?much? current passes through the power source?A?series?circuit?has?four?resistors.?The?current?through?one?resistor?is?810?mA.?How?much?current? is supplied by the source?You connect a switch in series with a 75-W bulb to a 120-V power source. a. What is the potential difference across the switch when it is closed (turned on)? b. What is the potential difference across the switch if it is opened (turned off)?Section 23.2A series-parallel circuit, similar to the one in Example Problem 4, has three resistors: one uses 2.0 W, the second 3.0 W and the third 1.5 W. How much current does the circuit require from a 12-V battery?If?the?13?lights?shown?in?Figure?14 are identical, which of them will burn brightest? A series-parallel circuit has three appliances on it. A blender and a stand mixer are in parallel, and a toaster is connected in series as shown in Figure?15. The series-parallel circuit has a total electric potential difference of 125 V. Find the current through the blender.How do the brightness of the bulbs compare?If I3?is?1.7?A?and?I1?is?1.1?A,?what?is?the?current?through?bulb?2?The?wire?at?point?C?is?broken?and?a?small?resistor?is?inserted?in?series?with?bulbs?2?and?3 (refer to Figure 17).?What?happens to the brightness of the two bulbs? Explain. A?voltmeter?connected?across?bulb?2?measures?3.8?V,?and?a?voltmeter?connected?across?bulb?3?measures?4.2?V.What?is?the?potential?difference?across?the?battery? Refer to Figure 17.PHYSICS 2019-20EXPLORATORY LABSELECTRICAL CIRCUITS: Light that BulbPurpose: To study various arrangements of a battery and bulbs and the effects of those arrangements on bulb brightness Required Equipment: size-D dry cell (battery) bare copper wire 3 flashlight bulbs 3 bulb holders Discussion: A dry cell (commonly called a battery) is a source of electric energy. Many arrangements are possible to get this energy from dry cells to flashlight bulbs. In this activity, you will test these arrangements to see which makes the bulbs brightest. Procedure: Step 1: Arrange one bulb (without a holder), one battery, and wire in as many ways as you can to make the bulb emit light. Sketch each of your arrangements, including failures as well as successes. Label the sketches of the successes. 1. Describe the similarities among your successful trials. Step 2: Use a bulb in a bulb holder (instead of a bare bulb), one battery, and wire. Arrange these in as many ways as you can to make the bulb light. 2. What two parts of the bulb does the holder make contact with? Step 3: Using one battery, light all three bulbs. Sketch each of your arrangements, and note the ones that work. PHYSICS 2019-20LAB ACTIVITYObserving Magnetic Fields & Measuring Magnet Strength Part 1: Observing Magnetic Fields Magnets have an invisible magnetic force, which is made up of invisible lines of force. These lines of force attract each other and other objects. While the naked eye cannot see these fields, with iron shavings, the fields are visible. In part 1 of this lab, you are going to view and draw the magnetic fields of varying shape magnets. 411479928986Procedure: Place the magnet on the table and mark on your paper, the location of North and South, if applicable. Put a piece of plain white paper over the magnet, and slip 2 rulers under the paper to help keep the paper level. (See photo.) Sprinkle the iron fillings over the sheet, evenly. On the same lab drawing, sketch the iron fillings patterns. This shows the “invisible” magnetic field lines! When you are done, carefully roll the paper to funnel the iron fillings back into the original container. Magnet Field Lines: Lab Drawings Bar Magnet Horseshoe Magnet 2 Bar Magnets: North Pole to North Pole: with an inch in between 2 Bar Magnets: North Pole to South Pole: with an inch in between Magnet: Your Choice (which one?) 2 Magnets: Describe how you place them. Your Choice (which ones?) Part 1 Post Lab Questions Why was paper used in between the iron filings and the magnet? From your observations of magnetic fields, describe what you observe about iron fillings around the poles. Extend to an Analogy: Even though you can’t see magnetic fields with your eyes, you know they exist because they affect things around them. Can you think of an analogy in life that is similar? Part 2: Measuring Strength of Magnets (& items they attract) As you may guess, not all magnets have the same strength. Nor do magnets attract different items in the same way. In part 2 of this lab, you will be finding a way to measure (quantitatively) this strength of attraction. Consider these questions as you begin. How could you measure strength systematically? How strong is the magnet? How far away will it work? Can a small magnet attract a paper clip from across the room? From across your desk? How can you find out how strong your magnet is? How can you quantify the strength of your magnet? When you play with magnets and various items, you may notice a difference in the attraction of some items compared to another. How can you test “how strong?” Some items stick and are harder to pull off the magnet, can you use this to help you quantify (count or measure) the strength? You will probably measure distance or angle, but how? Play with items in front of you, and come up with a way to measure magnet strength. Remember, your method should distinguish a variety of attractiveness. Procedure: Consider using thread and a protractor to find a way to measure the strength of a magnet, but feel free to ask for additional materials. Perform some trials, to develop an apparatus to test the strength of your magnet. Write your finalized procedure below so that an individual could replicate your experiment EXACTLY. 1. 2. 3. 4. 5. 6. 7. Look for items to test. Here is a list of some items you may want to try. wooden toothpick penny jewelry plastic cup paper clips thread needles or pins rubber bands elastic hair bands tin can (various sizes) glass aluminum foil crayon nail mitten paper school scissors tack staples bobby pin or barrette Pre-Lab Questions Predict: Which one item will have the strongest attraction? Predict: Which one item will have the weakest attraction? Data Collection: Begin testing materials, and record measurements in the data table below. Data Table Item Magnet #1 Measurement Magnet #2 Measurement Magnet #3 Measurement Part 2 Post Lab Questions How well did your procedure work for testing strength of magnets? How could you improve your procedure for testing magnet strength? What would you do differently if you could redo the experiment? Were your predictions correct? Why or why not? Can you tell by looking at something, how strongly it will be attracted to a magnet? Why or why not? What additional factors (extraneous variables) affect the strength of magnets? Why might testing the strength of magnets (or items) be important in real life? References (Accessed May 2012) “Exploring Magnetic Fields.” Science NetLinks. ‐magnetic‐fields/ “May the Force Be with You.” “Magnetic Fields Inquiry” Teacher Notes. Arbor Scientific. “Magnetic Fields.” ‐magneticfields.pdf Science Net Links ‐teacher‐sheets/exploring‐magnetic‐fields‐activity2/ ................
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