Physics: An Introduction Chapter 21 -- Practice Questions

Chapter 21: Electric Currents and Direct-Current Circuits
Practice Questions

The unit for measuring current is the

volt.

ohm.

ampere.

ohm-m.

The unit for measuring resistance is the

ampere.

volt.

ohm.

ohm-m.

In a simple circuit a voltage of 5 volts is applied across a resistance of 10 ohms. The current in the circuit is

50 A

5 A

.5 A

.1 A

The power dissipated in the resistor in the previous question is

.5 watts.

2.5 watts.

5 watts.

50 watts.

What is the power drawn from the battery in question 3?

.5 watt

2.5 watt

5 watt

50 watt

A flashlight bulb draws 2.5 amps when connected to two C cells (3 volts). What is its resistance?

.83 ohm

1 ohm

1.2 ohm

2.4 ohm

What is the power disipated in the bulb in question 6?

3 W

3.6 W

7.5 W

None of the above.

A lantern bulb with a resistance of 4 ohms draws 1.5 A when connected to a certain battery. The battery voltage is

1.5 V.

2.7 V.

4 V.

None of the above.

A 1000 watt appliance is used 10 hours a day for 28 days per month. If the cost of electricity is $.10 a kwh (kilowatt-hour), how much does it cost to operate the appliance for a month?

$10

$28

$67

$200

10.

What is the cost of electricity in mils/J if it costs $.10 per kwh? (A mil is 1/1000 cent).

zero

.00005

.0028

.17

11.

One billion electrons pass a certain point in a micro second. This coresponds to a current of

.00000016 A

.00016 A

1x10¹⁵

None of the above.

12.

Three amps corresponds to how many electrons per seconds?

1x10¹⁹

1.5x10¹⁹

1.9x10¹⁹

3x10¹⁹

13.

Two otherwise identical wires are made of different materials, the second having twice the resistivity of the first. The first has a resistance of 2 ohms, the second has a resistance of

1 ohm

3 ohms

4 ohms

Not enough information is given.

14.

Two aluminum wires have the same diameter but the second is twice as long as the first. If the first has a resistance of 2 ohms, the resistance of the second is

1 ohm.

3 ohms.

4 ohms.

8 ohms.

15.

Two copper wires have the same length but the second has twice the diameter of the first. If the resistance of the first is 2 ohms, the resistance of the second is

1/2 ohm.

1 ohm.

4 ohms.

8 ohms.

16.

What is the resistance of a 10 km long copper wire with a diameter of 4mm?

3.3 ohms

13.4 ohms

.013 ohms

.003 ohms

17.

If the wire in the above question has a resistance of 10 ohms and is transmitting 10 kW at 1000 volts how much power is lost in the wire?

10 W

100 W

1 kW

10 kW

18.

If the power in the above question is being transmitted at 10000 volts, what is the power loss in the wire?

1 W

10 W

1 kW

10 kW

19.

What is the equivalent capacitance of the two capacitors in series in the figure?

10 microF

20 microF

30 microF

40 microF

20.

What is the charge on the 30 microF capacitor in the circuit in question 19?

40 C

.00054 C

1389 C

.00018 C

21.

What is the voltage across C₂ (above)?

18 V

12 V

9 V

6 V

22.

You have three capacitors C₁= 15 pF, C₂= 35 pF and C₃= 50 pF. How can you arrange them to get an equivalent capacitance of 25 pF?

23.

What is the equivalent resistance to the three resistors on the left in the above figure?

10 ohms

9 ohms

5 ohms

4 ohms

24.

What is the current drawn from the battery in the circuit?

6 A

4 A

2 A

2/3 A

25.

What is the current through the 20 ohm resistor on the left in the figure?

1/15 A

2/15 A

3/15 A

4/15 A

26.

What is the voltage drop across the three resistors on the left in the circuit in the above question?

6 V

4 V

2 2/3 V

0 V

27.

What is the voltage drop across the 20 ohm resistor in the circuit?

6 V

4 V

2 V

0 V

28.

In the above question what is the current through the upper 10 ohm resistor?

1.5 A

0.6 A

0.3 A

0 A

29.

Close the switch in the above circuit by pressing the button below and find the time constant of the circuit.

t= seconds V= volts

3.0 seconds

4.5 seconds

6.0 seconds

9.2 seconds

30.

If the capacitor in the circuit in the above question is 3 microF, what is the resistance?

100 ohms

2000 ohms

300000 0hms

2 Meg ohms