Electrical Question 1
The number of kilowatts in 135 milliwatts is
- 1.35 × 10–4 kW
- 135 × 10–3 kW
- 0.0135 kW
- 0.00135 kW
Answer: A. 1.35 × 10–4 kW
Solution
The number of kilowatts in 135 milliwatts is
1 kW = 1000 watt
1 Watt = 10-3 Kilowatt
1 milliwatt = 10-3 watt
135 milliwatt = 135×10-3 watt
= 135×10-6 Kilowatt
= 1.35×10-4 Kilowatt
Electrical Question 2
An electric heater draws 3.5 A from a 110 V source. The resistance of the heating element is approximately-
- 385 Ω
- 38.5 Ω
- 3.1 Ω
- 31 Ω
Answer: D. 31 Ω
Solution
An electric heater is an example of a resistive load. We can apply Ohms law to any passive element.
According to Ohms law,
V = I.R
Current drawn from the supply
I = 3.5 A and V = 110 V
R = V/I
R = 110/3.5 = 31.428 Ω ≡ 31Ω
Electrical Question 3
A certain series circuit consists of a 1/8 W resistor, a 1/4 W resistor, and a 1/2 W resistor. The total resistance is 1200 Ω. If each resistor is operating in the circuit at its maximum power dissipation, the total current flow is
- 27 mA
- 2.7 mA
- 19 mA
- 190 mA
Answer: A. 27 mA
Solution
Total power consumption in the circuit is the sum of all the elements of power consumption.
Total power consumption = 1/8+1/4+1/2=0.875 Watt
The total resistance given in the circuit is 1200 Ω
Power consumption
P = V2/R
0.875×1200 = V2
V2 = 1050
V = √1050=32.4 Volt
Total current= Total voltage in the circuit/Total resistance in the circuit
I = 32.4/1200 = 0.027 A = 27 mA
Electrical Question 4
A series circuit consists of a 4.7 kΩ, a 12 kΩ, and a 2.2 kΩ resistor. The resistor that has the most voltage drop is
- 12 kΩ
- 2.2 kΩ
- 4.7 kΩ
- Impossible to determine from the given information
Answer: A. 12 kΩ
Solution
A series circuit consists of a 4.7 kΩ, a 12 kΩ, and a 2.2 kΩ resistor. The resistor that has the most voltage drop is dependent on two factors.
From Ohms law
V=IR
The voltage drop is dependent on two factors in a series circuit
- Current flowing in the element
- Resistance value
But in a series circuit, all the elements have the same current, so the maximum voltage drop occurs at, the resistance which is having more value among all.
∴ 12 KΩ resistance has highest voltage drop.
Electrical Question 5
The total resistance of a circuit is 680Ω. The percentage of the total voltage appearing across a 47 Ω resistor that makes up part of the total series resistance is
- 68%
- 47%
- 69%
- 6.91%
Answer: D. 6.91%
Solution
Total voltage = V
The total resistance in series combination is R+47 = 680
R = 680-47 = 633 Ω
From Ohms law
V=IR
The two-element series circuit is having the same current i.e., total current.
The total current I=V/680
The voltage drops across 47 Ω is
V47 = V/680×47
The percentage of the total voltage appearing across a 47 Ω
V47/V×100=47/680×100=6.91%
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