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AET DC Calculations
1. A circuit takes a steady current of 5 amperes for 40 minutes. Determine the
quantity of electricity supplied to the circuit.
2. An electroplating bath uses 18800 coulombs of electricity in 12 minutes.
Determine the current in amperes.
3. A battery uses 15 350 coulombs to fully charge at a constant current of 2.5
amperes. Determine the time in hours taken to fully charge the battery.
4. A circuit is connected to a DC power supply set to 12 volts. If the resistance of
the circuit is 24Ω determine the power taken by the circuit.
5. Determine the value of DC voltage that must be applied to a circuit of
56Ω resistance to cause a current of 500 milliamperes to flow in the circuit.
6. When a 12 volt battery is connected to a circuit, a current of 25 milliamperes is
measured to be flowing in the circuit. Determine the value of resistance of the
circuit.
7. A circuit has a measured current flow of 1.5 amperes when connected to a 12
volt DC battery. Determine the current that will flow if the same circuit is
connected to a 15 volt battery.
8. Determine the current in flowing in a circuit when a 22kΩ resistor is connected
to a 24 volt battery.
9. A circuit, when connected to a 240 V supply, has 250mA flowing through it.
Determine the resistance of the circuit
10. Determine the value of DC voltage that must be applied to a circuit of
470kΩ resistance to cause a current of 25µA to flow in the circuit.
11. A5.6kW lamps draws a current of 23 amps. Determine the voltage
12. A circuit has a measured current flow of 25mA when connected to a 50V DC
power supply. Determine the power taken by the circuit .
13. If 2.5A flows for 27 minutes, determine the quantity of electricity that has
been transferred in the circuit.
14. Determine the current that would need to flow in an electroplating bath if 40
500 coulombs of electricity is required for 2.5 hours.
15. If the power dissipation of a circuit is 3.6kW when connected to 240V supply,
determine the current flowing in the circuit.
16. Determine the resistance of a circuit which dissipates 1250W when connected
to a 240V supply.
17. A load dissipates 144W when connected to a 24V DC supply. Determine the
power dissipation when connected to a 32V supply.
18. Determine the power dissipated across a resistor of 27Ω when connected to a
240 volt DC supply.
19. When connected to a 110V DC supply, the current in a circuit is measured as
2.5A. Determine the power dissipation of the circuit.
20. An R-C circuit consists of a resistance of 180kW and a capacitance of 68µF.
Determine the time constant of the circuit
21. Determine the capacitance of a capacitor that is required to store a charge of
180µC when connected to a 36V supply
22. Determine the power output in kW of a hoist motor if it has to raise a load of
1958kg up the side of a 25 m building in 60 seconds.
23. An electric motor has a measured electrical power input of 1.2kW. If the
motor is rated at 240V, 1kW, determine the losses in the motor , and the
percentage efficiency of the motor.
24. A 350µF capacitor is connected in series with a 5k6Ω resistor, and the circuit
is connected to a 24V dc supply. For this circuit determine the capacitor
voltage after 3.92 seconds using the universal time constant curve
25. A circuit is made up of two resistors in parallel and has an equivalent
resistance of 15.23 Ω. If R1 has a resistance of 25 Ω, determine the resistance
of R2.
26. The output of a generator has been measured at 250kW, and the machine
losses have been determined as 25kW. Determine the power input to the
generator and the generators efficiency.
27. What is the maximum voltage that can be applied to a 12Ω, 5W resistor
without exceeding the power rating of the resistor?
28. * Determine the charge on a 47µF capacitor when connected to a 12V supply.
29. A 240V motor draws 25A when raising a 750kg load to a height of 13.6m in
20 seconds. Determine input power, the output power, the motor losses, and
the motor efficiency
30. * Determine the quantity of electricity required when a current of 7.5A flows
in a circuit for 90 seconds.
31. * Determine the time required to transfer 5400C of electricity with a current of
2.5A.
32. * Determine the current required to transfer 14 400C of electricity in 45
minutes
33. * Calculate the resistance of a copper conductor that has a resistivity of 1.72 X
10 -8 Ω/m, a length of 45 meters and a cross sectional area of 2.5 mm2 .
34. Determine the quantity of electricity transferred in a circuit if a current 2.0A
flows for 4.5 hours
35. If 15 000 coulombs of electricity are transferred in a circuit in 25 mins, how
much electricity will be transferred in 1.25 hours for the same current flow?
36. 1A capacitor has a capacitance of 20µF and when connected to the supply
stores a charge of 0.004C. Calculate the applied voltage
37. An electric motor has a measured electrical power input of 500W. If the
motor is rated at 240V, 350W, determine the losses in the motor , and the
percentage efficiency of the motor
38. Four resistors with values of 22 ohms, 120 ohms, 320 ohms and 440 ohms
are connected in parallel across a 120 volt d.c. power supply. Calculate the
total power
39. Four resistors of values 56 ohms, 82 ohms, 100 ohms and 33 ohms are
connected in series across a d.c. generator. If a total current of 35milli amperes
flows in the circuit determine the total power
40. The output of a generator has been measured at 175kW, and the machine
losses have been determined as 25kW. Determine the power input to the
generator and the generators efficiency.
41. A conductor has a resistance of 2.87Ω, a length of 250m and a cross-sectional
area of 1.5mm2. Determine the resistivity of the material
42. Determine the cross-sectional area of a 100m length of conductor having a
resistance of 80mΩ. The resistivity of the conductor is 1.72 x 10-8Ωm.
43. Calculate the resistance of a copper conductor that has a resistivity of 1.72 x
10 -8 Ω/m, a length of 70 meters and a cross sectional area of 35 mm2
44. A 20 microfarad capacitor is connected in parallel with a 40 microfarad
capacitor Determine the total capacitance
45. A 470 microfarad capacitor is connected in series with a 470 kilo ohm resistor.
Determine the time constant of this circuit
46. Calculate the length of a copper conductor that has a resistivity of 1.72 X 10 -8
Ω/m, a cross sectional area of 25 mm2 and of a resistance of 2.5 ohms
47. Two resistors of values 56 ohms, and 33 ohms are connected in parallel
connected to 120 volt dc supply. Determine the total current
48. If the total resistance of three resistors connected in series is 116 ohms,
resistor 1 is= 56 ohms, and resistor 3 is 33 ohms are connected in lel
connected to 120 volt dc supply. Determine the value of resistor 2
49. If the time taken to fully charge a 470µF capacitor is 28.2 seconds, determine
the value of the series resistor
50. Determine the charge on a 47µF capacitor when connected to a 12V supply
51. Three capacitors having capacitances of 20, 40 and 100µF, are connected in
parallel across a 400V supply. Determine the equivalent capacitance
52. Three capacitors having capacitances of 4, 6 and 12µF are connected in series
across a 120V supply. Calculate the equivalent capacitance
53. Two capacitors having a capacitance of 8 an 12µF respectively are connected
in parallel across a 250V supply. Determine the charge stored on each
capacitor
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AET DC Calculations
1
12000C
26
300W
51
2
26.11A
27
19.62kJ
52
3
1.7Hours
28
8kW
53
4
6W
29
200W, 83.3%
54
5
28 V
30
60V
55
6
480 Ω
31
39 Ω
56
7
3A
32
275kW,90.9%
57
8
1.09mA
33
7.75V
58
9
960 Ω
34
564µC
59
10
11.75V
35
6kW,5kW,1kW 60
83.3%
11
243.5V
36
200V
61
12
1.25W
37
150W,70%
62
13
4 050 C
38
852W
63
14
4.5A
39
33.2W
64
15
15A
40
200W,87.5%
65
16
46Ω
41
1.72 x 108Ω/m
66
17
256W
42
21.5mm2
67
18
2.13kW
43
0.0344 Ω
68
19
4 050 C
44
60µF
69
20
4.5A
45
220.9sec
70
21
15A
46
3633mm
71
22
5µF
47
5.78A
72
23
200W,83.3.%
48
27Ω
73
24
2.13kW
49
12kΩ
74
25
39 Ω
50
564µC
75
160µF
2µF
0.002C, 0.003C