Current Electricity Online Objective Test | Current Electricity Online Objective Test

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q1. A battery is connected with a potentiometer wire. The internal resistance of the battery is negligible. If the length of the potentiometer wire of the same material and radius is doubled then

A. None of these

B. Potential gradient does not change

C. Potential gradient becomes half

D. Potential gradient becomes two times

Answer : Option B
Explaination / Solution:

Potential gradient Is given by V/l. If V and l are constant, the potential gradient also remains constant. The change in the radius will cause a change in the current. This does not change the potential gradient.

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q2. A potential difference of 220 V is maintained across 12000

_{Ω}

rheostat. Then voltmeter V has a resistance of 6000

_{Ω}

and point C is at one fourth the distance from a to b. Then the reading of voltmeter is

A. 45 volt

B. 40 volt

C. 30 volt

D. 60 volt

Answer : Option B
Explaination / Solution:

Resistance R = 1/4R = 12000/4 = 3000 parallel. .

This is in series with Rbc.

The current in the circuit I = 220/11000 = 0.02A The reading of the voltmeter is the potential drop across Rp. V = 0.02 * 2000 = 40V

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q3. Figure shows current in a part of an electrical circuit. Then current I is

A. 2.5A

B. 0.5A

C. 1.5A

D. 2.1A

Answer : Option A
Explaination / Solution:

Using Kirchhoff’s junction rule at junction A,2 + 5 - 2 - 1 + IAB = 0;IAB = - 4A

The current IAB is directed away from the junction A. Using the junction rule at B 4 + 0.2 - 1.7 - I = 0;

I = 2.5A

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q4. Find the pd between A and B from the figure

A. 4V

B. 2V

C. 6V

D. 8V

Answer : Option A
Explaination / Solution:

The resistance in the arm CAD RCAD = 4 + 6 = 10Omega .

The resistance in the arm CBD RCBD = 6 + 4 = 10Omega

Since the resistances in both the arms are equal, the current splits equally in the arms.ICAD = ICBD = 4/2 = 2A.

The potential difference across A and C.VAC = VA - VC = ICAD * RAC = 2 * 4 = 8V

potential difference across B and C VBC = VB - VC = ICBD * RBC = 2 * 6 = 12V.The potential difference across A and B VBA = VB - VA = VBC - VAC = 12 - 8 = 4V.

Point B is at a higher potential when compared to A.

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q5. The figure shows an unbalanced Wheatstone bridge. To balance the bridge:

A. 48 ohm resistance should be increased to 50 ohm

B. 95Ω resistance should be reduced to 90 Ω

C. 15 ohm resistance should be reduced to 10 ohm

D. 8 ohm resistance should be increased to 10 ohm

Answer : Option B
Explaination / Solution:

To balance bridge

$\frac{15}{X} = \frac{8}{48}$

So X = 90

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q6. A current is passed though two coils connected in series. The potential difference across the first coil of resistance 2 ohm is 5 volt. If the potential difference across the second coil is 12.5 volt the resistance of the second coil is

A. 5 Ω

B. 12.5 Ω

C. 6 Ω

D. 7 Ω

Answer : Option A
Explaination / Solution:

The current in the circuit

$\begin{array}{l} I = \frac{V_{1}}{R_{1}} \\ I = \frac{5}{2} = 2.5 Ω \end{array}$

V1 =5 V is the p.d across the first coil of resistance R1=2Ω. The same current flows through the second coil of resistance X. . The p.d across the second coil V2 =12.5 V.

$\begin{array}{l} X = \frac{12.5}{I} \\ X = \frac{12.5}{2.5} = 5 Ω \end{array}$

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q7. In a meter bridge experiment a balance point is obtained at a distance of 60 cm from the left end when unknown resistance R is in a left gap and 8 ohms resistor is connected in the right gap. When the position of R and 8 ohm resistor is interchanged the balance point will be at distance of

A. 40 cm

B. 80 cm

C. 60 cm

D. 50 cm

Answer : Option A
Explaination / Solution:

$\begin{array}{l} \frac{R}{8} = \frac{l}{(100 - l)} \\ \frac{R}{8} = \frac{60}{40} \\ s o, \frac{8}{R} = \frac{40}{60} \end{array}$

The balance point when 8Ω is in the left gap will be 40 cm.

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q8. The Wheatstone bridge is balanced for four resistors R1,R2,R3 and R4 with a cell of emf 1.46 V. The cell is now replaced by another cell of emf 1.08 V. To obtain the balance again

A. All the four resistance should be changed

B. Both the resistance R1 and R4 should be changed

C. Resistance R4 should be changed only

D. No resistance needs to be changed

Answer : Option D
Explaination / Solution:

The balance point of the Wheatstone’s bridge is determined by the ratio of the resistances. The change in the e m f of the external battery will have no effect on the balance point.

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q9. If the length of the filament of a heater is reduced by 10% the power of the heater will

A. increase by about 19%

B. Increase by about 11%

C. decrease by about 29%

D. Increase by about 9%

Answer : Option B
Explaination / Solution:

The power is related to resistance as,

$\begin{array}{l} P \propto \frac{1}{R} \\ \frac{P_{2}}{P_{1}} = \frac{R_{1}}{R_{2}} \\ a l s o, R \propto L \\ ∴ \frac{P_{2}}{P_{1}} = \frac{L_{1}}{L_{2}} \\ \frac{P_{2}}{P_{1}} = \frac{L}{0.9 L} \\ \Rightarrow P_{2} \approx 0.11 P_{1} \end{array}$

So Power increases by 11%.

# Current Electricity # CBSE 12th Physics Prepare / Learn

Q10. A Wheatstone bridge is balanced for four resistors R1, R2, R3 and R4 with a Lech lanche cell between A and C and a galvanometer between B and D. The positions of the cell and the galvanometer are interchanged. The balance will

A. Not change

B. Change and can be obtained by changing R1

C. Change and can be obtained by changing R4

D. Change and can be obtained by changing R1 and R4

Answer : Option A
Explaination / Solution:

The balance point will not change . For balancing of wheatstone bridge four arms of resistors are responsible. Interchange the position of galvanometer and cell does not affect balancing of wheatstone bridge.

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