Wednesday , August 15 2018
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# Electrical DC Circuits MCQs

1) A DC circuit has ……….. as a load.

1. resistance
2. inductance
3. capacitance
4. all of the above
EXPLANATION
DC Circuit has no field changing effect. So, there will be no inductance and capacitance effect in the circuit.

2) The purpose of load in an electric circuit is to

1. increase the circuit current
2. utilize electrical energy
3. decrease the circuit current
4. none of the above
EXPLANATION
No answer description required for this question.

3) Electrical appliances are not connected in series because

1. series circuit is complicated
2. power loss is more
3. appliances have different current ratings
4. none of the above
EXPLANATION
No answer description required for this question.

4) Electrical appliances are connected in parallel because it

1. is a simple circuit
2. draws less current
3. results in reduced power loss
4. makes the operation of appliances independent of each other
EXPLANATION
No answer description required for this question.

5) Three resistance 14.5 Ω, 25.5 Ω and 60 Ω are connected in series across 200 V. What will be the voltage drop across 14.5 Ω

1. 29 V
2. 13.5 V
3. 14 V
4. 18 V
EXPLANATION
In this circuit, total current is calculated as

R = 14.5+25.5+60

R = 100 Ω

I = V/R

I = 200/100

I = 2 A

Now, voltage drop across 14.5 Ω resistance is

V = IR

V = 2×14.5

V = 29 V

6) Two bulbs B1 100 W, 200 V and B2 40 W, 200 V are connected in series across 200 V battery, the total circuit resistance will be

1. 1000 Ω
2. 400 Ω
3. 1400 Ω
4. 135 Ω
EXPLANATION
In this circuit,

For B1

P1 = V^2/R

R1 = V^2/P

R1 = (200)^2 / 100

R1 = 400 Ω

For B2

P2 = V^2/R

R2 = (200)^2 / 40

R2 = 1000 Ω

Total resistance in circuit R = R1 + R2

R = 1400 Ω

7) When the number of resistance are connected in parallel, the total resistance is

1. greater than the smallest resistance
2. between the smallest and greatest resistance
3. less than the smallest resistance
4. none of the above
EXPLANATION
No answer description required for this question.

8) When cells are arranged in parallel

1. the current capacity increases
2. the current capacity decreases
3. the e.m.f decreases
4. the e.m.f increases
EXPLANATION
No answer description required for this question.

9) A battery of 24 V is applied across terminals AB of the circuit as shown in figure. The current in 2 Ω resistor will be

1.  3 A
2.  6 A
3.  2.5 A
4. 1.5 A
EXPLANATION
Here first calculate total resistance

1/R1 = 1/6 + 1/6

R1 = 3 Ω

R2 = 3 Ω + 5 Ω

R2 = 8 Ω

1/R = 1/8 + 1/8

1/R = 1/4

R = 4 Ω

V = IR

I = V/R

I = 24/4

I = 6 A

10) A cell of e.m.f E is connected across a resistance R. The potential difference between the terminals of the cell is found to be V. The instant resistance of the cell is

1. 2(E – V)V/r
2. 2(E – V)r/E
3. (E – V)r
4. ((E – V)/V)r
EXPLANATION
No answer description required for this question.

11) An external resistance R is connected to a cell of internal resistance r. The maximum current flows in the external resistance when

1. R < r
2. R > r
3. R = r
4. none of the above
EXPLANATION
No answer description required for this question.

12) A wire has a resistance of 12 Ω. It is bent in the form of a circle. The effective resistance between the two points on any diameter of the circle is

1. 6 Ω
2. 3 Ω
3. 12 Ω
4. 24 Ω
EXPLANATION
Here, wire is connected by bending it in circle. After then, Taking two points at any diameter means circle is divided in two equal half that makes it parallel connected. So, 12 Ω is divided into two equal i.e. 6 Ω resistance each. By solving these two parallel connected resistance we get 3 Ω as equivalent resistance.

13) The total resistance of circuit by connecting 50 resistance of 1/4 Ω in parallel is

1. 50/4 Ω
2. 4/50 Ω
3. 200 Ω
4. 1/200 Ω
EXPLANATION
No answer description required for this question.

14) The internal resistance of a cell of e.m.f 2 V is 0.1 Ω. It is connected to a resistance of 3.9 Ω. The voltage across the cell is

1. 0.5 V
2. 1.95 V
3. 1.9 V
4. 2 V
EXPLANATION
Here Current I = (E / (r+R) )

I = 2 / (3.9+0.1)

I = 2 / 4

I = 0.5

15) If in a electrical DC circuit, a supply of 180 V is connected across terminal AB as shown in figure below, then the current in 6 Ω resistor will be

1. 10 A
2. 5 A
3. 12 A
4. 6 A