Alternating Current NEET MCQ

1. What differentiates Alternating Current (AC) from Direct Current (DC)?

a) AC is used only in batteries
b) AC can’t be converted to DC
c) AC changes direction periodically
d) DC is more dangerous than AC

Answer:

c) AC changes direction periodically

Explanation:

The primary difference is that AC changes its direction periodically while DC flows in a constant direction.

2. The standard frequency of AC in most countries is:

a) 30 Hz
b) 40 Hz
c) 50 Hz
d) 60 Hz

Answer:

c) 50 Hz

Explanation:

In most countries, the standard frequency of AC is 50 Hz, though some, like the USA, use 60 Hz.

3. The average value of AC over one complete cycle is:

a) Maximum
b) Zero
c) Half of the peak value
d) Equal to peak value

Answer:

b) Zero

Explanation:

Over one complete cycle, the positive half cancels out the negative half, resulting in an average value of zero.

4. The effective or RMS value of an AC is:

a) 0.5 times the peak value
b) 0.707 times the peak value
c) Equal to the peak value
d) Twice the peak value

Answer:

b) 0.707 times the peak value

Explanation:

RMS (Root Mean Square) value is approximately 0.707 times the peak value for a sinusoidal AC.

5. In a purely resistive AC circuit, the phase difference between current and voltage is:

a) 0 degrees
b) 45 degrees
c) 90 degrees
d) 180 degrees

Answer:

a) 0 degrees

Explanation:

In a purely resistive circuit, the current and voltage are in phase, resulting in a phase difference of 0 degrees.

6. In an AC circuit with only capacitance, the current leads the voltage by:

a) 0 degrees
b) 45 degrees
c) 90 degrees
d) 180 degrees

Answer:

c) 90 degrees

Explanation:

In a purely capacitive circuit, the current leads the voltage by a phase difference of 90 degrees.

7. Which device allows AC to pass but blocks DC?

a) Diode
b) Inductor
c) Capacitor
d) Resistor

Answer:

c) Capacitor

Explanation:

A capacitor blocks DC and allows AC to pass through.

8. The impedance in an LCR circuit is given by:

a) R + XL + XC
b) R^2 + (XL + XC)^2
c) R^2 + (XL – XC)^2
d) √(R^2 + (XL – XC)^2)

Answer:

d) √(R^2 + (XL – XC)^2)

Explanation:

Impedance, Z, in an LCR circuit is given by Z = √(R^2 + (XL – XC)^2).

9. In an AC circuit with only inductance, the voltage leads the current by:

a) 0 degrees
b) 45 degrees
c) 90 degrees
d) 180 degrees

Answer:

c) 90 degrees

Explanation:

In a purely inductive circuit, the voltage leads the current by a phase difference of 90 degrees.

10. Power factor in an AC circuit is defined as:

a) R/Z
b) XL/Z
c) XC/Z
d) XL – XC

Answer:

a) R/Z

Explanation:

Power factor is the cosine of the phase difference, defined as the ratio of resistance to impedance, i.e., cos(Φ) = R/Z.

11. The power consumed in a purely capacitive circuit is:

a) Maximum
b) Zero
c) Half of the input power
d) Equal to the input power

Answer:

b) Zero

Explanation:

In a purely capacitive circuit, the power consumed is zero as the phase difference between current and voltage is 90 degrees.

12. In a series LCR circuit at resonance, the impedance is:

a) Maximum
b) Minimum
c) Equal to resistance R
d) Infinite

Answer:

c) Equal to resistance R

Explanation:

At resonance in a series LCR circuit, XL = XC, so impedance Z equals the resistance R.

13. Resonance in an AC circuit means:

a) Maximum impedance
b) Minimum impedance
c) Maximum current
d) Both b) and c)

Answer:

d) Both b) and c)

Explanation:

At resonance, the impedance is minimum, and current is maximum in a series LCR circuit.

14. The unit of reactance is:

a) Ohm
b) Henry
c) Farad
d) Joule

Answer:

a) Ohm

Explanation:

Reactance (both capacitive and inductive) is measured in Ohms.

15. Which of the following is not a type of transformer?

a) Step-up
b) Step-down
c) Step-side
d) Power

Answer:

c) Step-side

Explanation:

There's no such thing as a 'step-side' transformer. Common types include step-up, step-down, and power transformers.

16. In an AC generator, the produced EMF is directly proportional to:

a) Speed of rotation
b) Number of turns
c) Both a) and b)
d) Neither a) nor b)

Answer:

c) Both a) and b)

Explanation:

The induced EMF in an AC generator is directly proportional to the speed of rotation and the number of turns in the coil.

17. In a pure inductance, the power factor is:

a) 0
b) 0.5
c) 1
d) Undefined

Answer:

a) 0

Explanation:

For a purely inductive circuit, the power factor is zero, as the phase difference between current and voltage is 90 degrees.

18. In a transformer, the number of turns in the primary coil compared to the secondary coil determines:

a) The type of current
b) The phase difference
c) The stepping up or stepping down of voltage
d) The power factor

Answer:

c) The stepping up or stepping down of voltage

Explanation:

In a transformer, the ratio of the number of turns in the primary coil to the secondary coil determines whether the voltage is stepped up or stepped down.

19. The phenomenon of a current in the primary coil inducing a current in the secondary coil without any direct connection is called:

a) Self-induction
b) Mutual induction
c) Reactance
d) Impedance

Answer:

b) Mutual induction

Explanation:

Mutual induction is the phenomenon where a change in current in one coil induces a voltage in a nearby coil.

20. Choke in a tube light is essentially a:

a) Capacitor
b) Resistor
c) Diode
d) Inductor

Answer:

d) Inductor

Explanation:

The choke in a tube light is essentially an inductor used to regulate the current in the circuit.

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