Important Alternating Current NEET Questions from Previous Years

Q 1 :
A step up transformer is connected to an AC mains supply of 220 V to operate at 11000 V, 88 watt. The current in the secondary circuit, ignoring the power loss in the transformer is [2024]

8 mA
4 mA
0.4 A
4 A

1

2

3

4

(1)

Given, $V_{P} = 220$ $V;$ $V_{S} = 11000$ $V;$ $P_{S} = 88$ $W$

We know, $P_{S} = V_{S} I_{S}$

$88 = 11000 \times I_{S} or \frac{88}{11000} = I_{S}$

$∴ I_{S} = 8 \times 10^{- 3}$ $A = 8$ $mA$

Q 2 :
In an ideal transformer, the turns ratio is $\frac{N_{p}}{N_{s}} = \frac{1}{2}$ . The ratio $V_{s} : V_{p}$ is equal to (the symbols carry their usual meaning) [2024]

1 : 2
2 : 1
1 : 1
1 : 4

1

2

3

4

(2)

Here, $\frac{N_{p}}{N_{s}} = \frac{1}{2}$

For ideal transformer, $\frac{N_{p}}{N_{s}} = \frac{V_{p}}{V_{s}}$

$\Rightarrow \frac{1}{2} = \frac{V_{p}}{V_{s}} \Rightarrow \frac{V_{s}}{V_{p}} = \frac{2}{1}$

Q 3 :
A 12 V, 60 W lamp is connected to the secondary of a step down transformer, whose primary is connected to ac mains of 220 V. Assuming the transformer to be ideal, what is the current in the primary winding? [2023]

3.7 A
0.37 A
0.27 A
2.7 A

1

2

3

4

(3)

[IMAGE 263]

Let current in the primary is $I_{p} .$

As, the transformer is ideal

$∴$ $P_{i} = P_{0}$

$\Rightarrow 220 \times I_{p} = 60$

$\Rightarrow I_{p} = \frac{60}{220} = \frac{6}{22} = \frac{3}{11} = 0.27$ $A$

Q 4 :
A step down transformer connected to an AC mains supply of 220 V is made to operate at 11 V, 44 W lamp. Ignoring power losses in the transformer, what is the current in the primary circuit? [2021]

4 A
0.2 A
0.4 A
2 A

1

2

3

4

(2)

Here, $P = 44$ $W,$ $V_{p} = 220$ $V,$ $V_{s} = 11$ $V$

Power, $P = V_{s} I_{s}$

$44 = 11 \times I_{s} \Rightarrow I_{s} = \frac{44}{11} = 4$ $A$

Now, $V_{p} I_{p} = V_{s} I_{s}$

$220 \times I_{p} = 11 \times 4 \Rightarrow I_{p} = \frac{11 \times 4}{220} = \frac{4}{20} = 0.2$ $A$

Q 5 :
A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are [2014]

300 V, 15 A
450 V, 15 A
450 V, 13.5 A
600 V, 15 A

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2

3

4

(2)

Here, Efficiency of the transformer, $η = 90 %$

Input power, $P_{in} = 3 kW = 3 \times 10^{3} W = 3000 W$

Voltage across the primary coil, $V_{p} = 200 V$

Current in the secondary coil, $I_{s} = 6 A$

As $P_{in} = I_{p} V_{p}$

$∴$ $Current in the primary coil, I_{p} = \frac{P_{in}}{V_{p}} = \frac{3000 W}{200 V} = 15 A$

Efficiency of the transformer,

$η = \frac{P_{out}}{P_{in}} = \frac{V_{s} I_{s}}{V_{p} I_{p}} ∴ \frac{90}{100} = \frac{6 V_{s}}{3000}$ or $V_{s} = \frac{90 \times 3000}{100 \times 6} = 450 V$

Topic Question Set

Q 1 :
A step up transformer is connected to an AC mains supply of 220 V to operate at 11000 V, 88 watt. The current in the secondary circuit, ignoring the power loss in the transformer is [2024]

Q 2 :
In an ideal transformer, the turns ratio is $\frac{N_{p}}{N_{s}} = \frac{1}{2}$ . The ratio $V_{s} : V_{p}$ is equal to (the symbols carry their usual meaning) [2024]

Q 3 :
A 12 V, 60 W lamp is connected to the secondary of a step down transformer, whose primary is connected to ac mains of 220 V. Assuming the transformer to be ideal, what is the current in the primary winding? [2023]

Q 4 :
A step down transformer connected to an AC mains supply of 220 V is made to operate at 11 V, 44 W lamp. Ignoring power losses in the transformer, what is the current in the primary circuit? [2021]

Q 5 :
A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are [2014]

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Topic Question Set

Q 1 : A step up transformer is connected to an AC mains supply of 220 V to operate at 11000 V, 88 watt. The current in the secondary circuit, ignoring the power loss in the transformer is [2024]

Q 2 : In an ideal transformer, the turns ratio is NpNs=12. The ratio Vs:Vp is equal to (the symbols carry their usual meaning) [2024]

Q 3 : A 12 V, 60 W lamp is connected to the secondary of a step down transformer, whose primary is connected to ac mains of 220 V. Assuming the transformer to be ideal, what is the current in the primary winding? [2023]

Q 4 : A step down transformer connected to an AC mains supply of 220 V is made to operate at 11 V, 44 W lamp. Ignoring power losses in the transformer, what is the current in the primary circuit? [2021]

Q 5 : A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are [2014]

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Q 1 :
A step up transformer is connected to an AC mains supply of 220 V to operate at 11000 V, 88 watt. The current in the secondary circuit, ignoring the power loss in the transformer is [2024]

Q 2 :
In an ideal transformer, the turns ratio is $\frac{N_{p}}{N_{s}} = \frac{1}{2}$ . The ratio $V_{s} : V_{p}$ is equal to (the symbols carry their usual meaning) [2024]

Q 3 :
A 12 V, 60 W lamp is connected to the secondary of a step down transformer, whose primary is connected to ac mains of 220 V. Assuming the transformer to be ideal, what is the current in the primary winding? [2023]

Q 4 :
A step down transformer connected to an AC mains supply of 220 V is made to operate at 11 V, 44 W lamp. Ignoring power losses in the transformer, what is the current in the primary circuit? [2021]

Q 5 :
A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are [2014]