NZIP 2008: Questions & Answers



Name:_________________

Assignment due:

Waimea College

PHYSICS

Electricity Homework Assignment 1

DC Circuits

Level 3

90523 Demonstrate understanding of electrical systems

Credits: Six

You may find the following formulae useful

E = ½QV Q = CV [pic] ( = RC

CT = C1 + C2 + C3 + ….. [pic]

( = BA [pic] [pic] [pic]

[pic] E = ½LI2 [pic]

I = Imaxsin(t V = Vmaxsin(t [pic] [pic]

[pic] XL = (L V = IZ ( = 2(f

NZIP 2008

Question two: SOLAR PANEL CHARGING SYSTEM

Interest in home solar power systems, with a view to disconnecting from the national grid, has risen in recent times. Such a system could look as shown in the diagram below:

[pic]

The system involves roof-mounted solar panels, which operate a 12.0 V DC system for lights, household appliances and entertainment. Excess energy is stored in a battery of cells installed in the garage.

(a) Show that the current flowing from the solar panels, when they are operating at maximum power output, is 83.3 A.

(b) Explain, in terms of the appropriate Kirchhoff’s Law, what the voltage across the storage battery terminals will be.

In a family home in which this system is installed, Dad becomes addicted to X-box and one evening completely drains the batteries. Next morning being a brilliantly sunny day, the process of charging the battery can take place.

(c) Write an equation to show how the three currents relate to each other.

(d) Show that when the switch is closed and the solar panels can operate at full power output the maximum current that can flow through to the storage battery is 48.3 A.

(e) When the storage cells are completely discharged the total internal resistance of the battery is 95.4 m(. In the totally discharged state maximum current flows through the battery. Calculate the EMF of the battery when it is discharged. Give your answer to the correct number of significant figures.

EMF =

NZIP 2007

Question two: LOOP CIRCUITS

[pic]

(a) State Kirchhoff’s law relating to the currents in this circuit.

(b) If I3 is 2.5 A, calculate I2.

NZIP 2006

QUESTION TWO:

The diagram shows the circuit representation of an electric cell. The letter ε stands for the emf of the cell and r its internal resistance.

(a) Explain what the term “emf” means.

The diagram shows a cell of internal resistance 2.6 ( connected across a light bulb whose power output is 0.62 W when a current 0.27 A flows through it.

(b) Calculate the value of the emf of the cell. State your answers to the correct number of significant figures.

emf =

The diagram shows two cells connected in parallel across a light bulb. The current through the branch AB is 0.18 A. The currents through the other branches are I1 and I2 as indicated in the diagram

(c) Using Kirchhoff’s law explain why the current I1 = I2 + 0.18A at junction D.

(d) Use Kirchhoff’s law to calculate the values of the currents I1 and I2.

I1 = ____________ I2 = ____________

NZIP 2005

QUESTION ONE:

Joanne and Tamihana have a camper van that uses two normal car batteries. They are both fixed in the engine bay. Normally one is used for vehicle operations and the other for cabin appliances (CD player, lights, etc).

After a long drive, both batteries are recharged. Tamihana wants to connect both batteries together to improve the operation of the cabin lights. The diagram below shows how he did this.

Tamihana connects the batteries as shown:

[pic]

The following diagram shows the circuit in more detail. Use it to answer question (a) and question (b).

[pic]

(a) Use Kirchoff’s Voltage Law in the loop BCDEB to show that the current I2 = 2.05A.

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(b) Use Kirchoff’s Current Law to find the current I1.

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(c) Describe a measurable change that occurs inside the battery when it goes flat.

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Assessor’s use only

Assessor’s use only

12.0 V solar panel system,

1.00 ( 103 W maximum power output

Total household resistance,

RT = 0.343 (

I2

I3

I1

EMF

r

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