# Physics — Practice Problems: DC Circuits Page 1 of 3...

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Physics — Practice Problems: DC Circuits Page 1 of 3

AP Physics 1 and 2:

Circuits: I = Δq/Δt V = IR R = L/A P = IV = V2/R = I2R

Req series =R1+R2+….. Same I, share V

(1/Req parallel) = (1/R1)+(1/R2 )+….. Same V, share I

Kircchoff’s rules: Junction rule: (charge conservation): at any junction: Iin = Iout

Loop rule: (energy conservation): for a closed path: ΔV = 0

AP Physics 1 and 2:

1. A 9-V battery is connected to a bulb whose resistance is 300. How many electrons leave the battery per minute?

2. A copper wire has a radius r and length L. Its resistance is R. What is the resistance of a second copper wire of radius r/2 and

length 3L?

3. What is the maximum voltage that can be applied to a 330-resistor rated at 1/2 W?

4. At $0.1 per kWh, how much does it cost to leave a 40-W light on all day for a week?

5. How many 40-W light bulbs, operated at 120V, can be used without blowing a 10-A fuse

AP Physics 2:

6. A power station delivers 1200 kW of power to a factory through 2 wires at 40,000 V. How much power is lost to the wires?

AP Physics 1 and 2: 7 a) b) c) d), 8

AP Physics 2: 7 e), 9, 10

7. Each of the resistors shown below is 30 Find equivalent resistance for each of the following circuits:

a) b) c)

d)

e)

8. Find the electric current through, voltage across, and power of each resistor.

a) b) c) d)

9. What is the internal resistance of a 10-V battery whose terminal voltage drops to 9.5V when there is a 2-A current going through

the battery?

10. A battery has an emf of 10V and an internal resistance of 1 . What is the terminal voltage of the battery when it is connected to

a circuit whose net resistance is 15 ?

AP Physics 1 and 2: 11. You need to know how to connect an ammeter and a voltmeter to a circuit.

AP Physics 2: 12. Consider the circuit on the right. Answer qualitatively: a) What happens to the voltage across each resistor

when the switch S is closed? b) What happens to the current through each resistor when the switch S is

closed? c) What happens to the power of each resistor when the switch S is closed?

13. The circuit on the right has been connected for a long time. Calculate

a) the current in the 4resistor, b) the potential difference across the 8 resistor,

and c) The charge stored on one plate of the 6nF capacitor.

14. Consider the circuit on the right. Initially switch S1 is closed and switch S2 is open.

Find a) the reading of the voltmeter.

Switch S1 is then opened and switch S2 is closed. A long time later, find b) the reading of the voltmeter

and c) the charge on the capacitor.

2

9V

3

1

2

9V

3

1

2

9V

3 1

2

9V

3

1

3nF

9V

8

6nF

4

15

9V

10

S

8

80

12V

5nF

80 V S1

S2

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