1. A 10 V
battery supplies a resistive load of 10 ohms for 1 minute. What is the power
supplied?
A.
100 W. B. 10
V A. C. 10 W.
Answer.
10 W. Explanation. Power = I2R (time is not required). Resistive
load only, so answer is in Watts.
2. A resistor
dissipates 80 Watts. If it runs for 4 hours 15 minutes, how much energy is
dissipated in total?
A.
20. 4 kJ. B. 1.
224 MJ. C. 191. 25 J.
Answer.
1. 224 MJ. Explanation. Energy = Power * Time. Time must be in
seconds. There are 3600 seconds in 1 hour - not 60.
3. The earth
lead of a 24 V equipment is 0. 5 ohm resistance and carries 80 A. How
much power does it dissipate?
A.
1. 92 kW. B. 1.
152 kW. C. 3. 2 kW.
Answer.
3. 2 kW. Explanation. Power = I2R. Since it is an earth lead it will
not have the full 24V on it, so disregard voltage.
4. What is the
power dissipated in a 500 ohm resistor with a 3A flow?
A.
4. 5 kW. B. 1.
5 kW. C. 750 kW.
Answer.
4. 5 kW. Explanation. Power = I2R.
5. A DC
circuit containing a total resistance of 100 ohms has a current flow of 250 m A. The
power dissipated in the circuit is.
A.
0. 4 watts. B. 5
watts. C. 6. 25 watts.
Answer.
6. 25 watts. Explanation. Power = I2R.
6. Power is
the rate of doing work. It is measured in.
A.
joules/second. B. joules
* seconds. C. watts/second.
Answer.
joules/second.
7. The power
in a circuit when voltage and resistance is given can be found by.
A.
V*R. B. V*V*R.
C. V*V / R.
Answer.
V*V / R. Explanation. Power = V2 /R.
8. A 500 ohm
resistor carries a 3 amp current. What is the power dissipated?
A.
500 W. B. 5
kW. C. 4. 5 kW.
Answer.
4. 5 kW. Explanation. Power = I2 R.
9. A 3 ohm
resistor dissipates 27 Watts. How much current flows through it?
A.
9 A. B. 0.
15 A. C. 3 A.
Answer.
3 A. Explanation. power = I2 R. Transpose for I. ";.
10. A 48-volt
source is required to furnish 192 watts to a parallel circuit consisting of
three resistors of equal value. What is the value of each resistor?
A.
4 ohm. B. 36
ohm. C. 12 ohm.
Answer.
36 ohm. Explanation. Each resistor dissipates 192/3 = 64 Watts.
Voltage is the same across all resistors in parallel = 48 Volts. Power =
V-squared/R. Work out R.
11. A piece of
equipment is rated at 750 watts and the applied voltage is 30 volts. The value
of the protection fuse should be.
A.
20 amps. B. 15
amps. C. 30 amps.
Answer.
30 amps. Explanation. Power = amps * volts. Find the amperage from
that. Then choose the fuse of the nearest size up.
12. How much
power must a 24-volt generator furnish to a system which contains the following
series loads? 5 ohm, 3 ohm and 12 ohm.
A.
402 watts. B. 28.
8 watts. C. 450 watts.
Answer.
28. 8 watts.
13. A direct
current of 12 milliamperes flows through a circuit which has a resistance of
1000 ohms. The power dissipated by the circuit is.
A.
144 milliwatts. B. 12
watts. C. 12 milliwatts.
Answer.
144 milliwatts. Explanation. Power = I2 R. Watch the prefix 'milli'.
'Milli' means divide by 1000. Square it and you must divide by 1,000,000.
14. In a power
circuit, the purpose of an inductor is.
A.
to dampen
voltage surges. B. to dampen current surges. C. to dampen power surges.
Answer.
to dampen power
surges.
15. In the
circuit shown, the power developed across the 10 kilo ohm resistor is.
A.
250 mW. B. 250
W. C. 50 mW.
Answer.
250 mW. Explanation. Power = I2 R = 0. 005 * 0. 005 * 10,000 = 0.
000,025 * 10,000 = 0. 25W = 250mW.
16. A single
phase circuit has an input voltage of 100V. The current is 10A and the circuit
has a power factor of 0. 5. The true power is.
A.
50W. B. 1000W.
C. 500W.
Answer.
500W. Explanation. Apparent Power = IV = 100 * 10 = 1000 V A. True
Power = PF * Apparent Power = 0. 5 * 1000 = 500W.
17. Power in a
DC circuit is found by.
A.
multiplying the
voltage by itself and dividing by the current. B. multiplying current by resistance. C. multiplying the resistance by the current
squared.
Answer.
multiplying the
resistance by the current squared.
18. If the
energy supplied to a circuit for 4hrs 15 minutes at 800 j/sec what would be the
energy consumed?
A.
3400 KW Hrs. B. 3.
4 KW Hrs. C. 340 KW Hrs.
Answer.
3. 4 KW Hrs. Explanation. 4
hours 15 minutes = 4 1/4 hours. Energy = power * time = 800 * 4 1/4 = 3400 = 3.
4 kW hrs.
19. A heater
which consumes 800 Kilojoules/sec is on for 4hrs 15min. The energy consumed is.
A. 340 kWh. B. 3. 4 kWh. C. 3400 kWh.
Answer.
3400 kWh. Explanation. kJ/s = kW. 800 * 4. 25 = 3400 kWh.
20. A voltage
of 250V causes a current of 30m A.
What is the
wattage?
A.
7. 5W. B. 7500W.
C. 0. 225W.
Answer.
7. 5W. Explanation. Power = IV = 30/1000 * 250 = 7. 5W.
21. Which
requires the most electrical power during operation?
A.
A 12-volt motor
requiring 8 amperes. B. Four 30-watt lamps in a 12-volt parallel
circuit. C. Two lights requiring
3 amperes each in a 24volt parallel system.
Answer.
Two lights
requiring 3 amperes each in a 24volt parallel system. Explanation. a
is 12*8=96W, b is 30*4 = 120W, c is 3*24*2=144W.
22. The power
dissipated in a circuit with a known potential difference and resistance is
calculated by.
A.
multiplying the
square of the potential difference by the resistance. B. dividing
the square of the potential difference by the resistance. C. finding the current and multiplying the answer
by the resistance.
Answer.
finding the
current and multiplying the answer by the resistance. OR dividing the square of
the potential difference by the resistance.
23. The power
expended in a given circuit is.
A. inversely
proportional to cube-root of the current. B. proportional to the square-root of the
voltage. C. proportional to the
square of the voltage.
Answer.
proportional to
the square of the voltage.