Circuit Networks(12th Grade > Physics ) Questions and answers for exam Preparation

12th Grade > Physics

CIRCUIT NETWORKS MCQs

Total Questions : 30 | Page 3 of 3 pages

Question 21. In Wheatstone's bridge P=9ohm, Q=11ohm, R=4ohm and S=6ohm. How much resistance must be put in parallel to the resistance S to balance the bridge

24 ohm
449 ohm
26.4 ohm
18.7 ohm

Discuss Question

Answer: Option C. -> 26.4 ohm
:
C

\frac{P}{Q} = \frac{R}{S^{'}}

(For balancing bridge)

\Rightarrow S^{'} = \frac{4 \times 11}{9} = \frac{44}{9}

\Rightarrow \frac{1}{S^{'}} = \frac{1}{r} + \frac{1}{6}

\Rightarrow \frac{9}{44} - \frac{1}{6} = \frac{1}{r}

\Rightarrow r = \frac{132}{5} = 26.4 Ω

In Wheatstone's Bridge P=9ohm, Q=11ohm, R=4ohm And S=6ohm. H...

Question 22. What will be the equivalent resistance of circuit shown in figure between points A and D

10Ω
20Ω
30Ω
40Ω

Discuss Question

Answer: Option C. -> 30Ω
:
C
The equivalent circuit of above fig between A and D can be drawn as

R_{e q} = 10 + 10 + 10 = 30 Ω

Question 23. In the circuit shown here

E_{1} = E_{2} = E_{3} = 2 V

and

R_{1} = R_{2} = 4 Ω

. The current flowing between point A and B through battery

E_{2}

In The Circuit Shown Here E1=E2=E3=2V And R1=R2=4Ω. The Cur...

Zero
2 A from A to B
2 A from B to A
None of these

Discuss Question

Answer: Option B. -> 2 A from A to B
:
B
The equivalent circuit can be drawn as since

E_{1}

and

E_{3}

are parallely connected

So current

i = \frac{2 + 2}{2} = 2 A m p

from A to B

Question 24. A torch bulb rated as 4.5 W, 1.5 V is connected as shown in the figure. The emf of the cell needed to make the bulb glow at full intensity is

4.5 V
1.5 V
2.67 V
13.5 V

Discuss Question

Answer: Option D. -> 13.5 V
:
D
When bulb glows with full intensity, potential difference across it is 1.5 V. So current through the bulb and resistance of

1 Ω

are 3 A and 1.5 A respectively. So main current from the cell i = 3 + 1.5 = 4.5 A. By using

E = V + i r \Rightarrow E = 1.5 + 4.5 \times 2.67 = 13.5 V

Question 25. The figure shows a circuit diagram of a ‘Wheatstone Bridge’ to measure the resistance G of the galvanometer. The relation

\frac{P}{Q} = \frac{R}{G}

will be satisfied only when

The Figure Shows A Circuit Diagram Of A ‘Wheatstone Bridge...

The galvanometer shows a deflection when switch S is closed
The galvanometer shows a deflection when switch S is open
The galvanometer shows no change in deflection whether S is open or closed
The galvanometer shows no deflection

Discuss Question

Answer: Option C. -> The galvanometer shows no change in deflection whether S is open or closed
:
C
In balance condition, no current will flow through the branch containingS.

Question 26. In the circuit shown below

E_{1} = 4.0 V, R_{1} = 2 Ω, E_{2} = 6.0 V, R_{2} = 4 Ω

and

R_{3} = 2 Ω

. The current

I_{1}

In The Circuit Shown Below E1 = 4.0 V,R1=2Ω ,E2= 6.0 ...

1.6 A
1.8 A
1.25 A
1.0 A

Discuss Question

Answer: Option B. -> 1.8 A
:
B
Applying Kirchhoff's law for the loops (1) and (2) as shown infigure For loop(1)

- 2 i_{1} - 2 (i_{1} - i_{2}) + 4 = 0 \Rightarrow 2 i_{1} - i_{2} = 2 . . . . (i)

For loop (2)

- 2 (i_{1} - i_{2}) + 4 i_{2} - 6 = 0 \Rightarrow - i_{1} + 3 i_{2} = 3 . . . (i i)

On solving equation (i) and (ii)

i_{1} = 1.8 A .

Question 27. The magnitude and direction of the current in the circuit shown will be

73 A from a to b through e
73 A from b and a through e
1.0 A from b to a through e
1.0 A from a to b through e

Discuss Question

Answer: Option D. -> 1.0 A from a to b through e
:
D
Current

i = \frac{10 - 4}{3 + 2 + 1} = 1 A

from a to b via e

Question 28. The balancing length for a cell is 560 cm in a potentiometer experiment. When an external resistance of 10 ohm is connected in parallel to the cell the balancing length changes by 60 cm. The internal resistance of the cell in ohms is

1.6
1.4
1.2
0.12

Discuss Question

Answer: Option C. -> 1.2
:
C

\frac{r}{R} = \frac{l_{1} - l_{2}}{l_{2}}

here R=10 ohm

l_{1}

= 560cm

l_{2}

=560-60=500cm

r = R \times (\frac{l_{1} - l_{2}}{l_{2}})

= 10 \times (\frac{560 - 500}{500})

=1.2ohm

Question 29. In the network shown in the figure each of resistance is equal to

2 Ω

. The resistance between A and B is

In The Network Shown In The Figure Each Of Resistance Is Equ...

Discuss Question

Answer: Option B. -> 2Ω
:
B

Taking the portion COD is figure to outside the triangle (left), the above circuit will be now as resistance of each is

2 Ω

the circuit will behaves as a balanced wheatstone bridge and no current flows through CD. Hence

R_{A B} = 2 Ω

Question 30. For comparing the e.m.f.'s of two cells with a potentiometer, a standard cell is used to develop a potential gradient along the wires. Which of the following possibilities would make the experiment unsuccessful.

The e.m.f. of the standard cell is larger than the E e.m.f.'s of the two cells
The diameter of the wires is the same and uniform throughout
The number of wires is ten
The e.m.f. of the standard cell is smaller than the e.m.f.'s of the two cells

Discuss Question

Answer: Option D. -> The e.m.f. of the standard cell is smaller than the e.m.f.'s of the two cells
:
D
The emf of the standard cell must be greater than that of experimental cells, otherwise balance point is not obtained.