## Class 12 Physics MCQs Alternating Current for JEE/NEET

Here, you will get Class 12 Physics MCQ of Chapter 7 Alternating Current for cracking JEE and NEET/AIIMS. By solving these MCQs of Class 12 Physics Chapter 7 Alternating Current, you will get the confidence to crack JEE or NEET. Practice MCQ Questions for Class 12 Physics with Answers on a daily basis and score well in exams.

## Alternating Current Class 12 MCQs Questions with Answers

Energy dissipates in LCR circuit in
(a) L only
(b) C only
(c) R only
(d) All of the above

What is the ratio of inductive and capacitance reactances in an ac circuit?
(a) 1
(b) ω²L
(c) ω²LC
(d) l

A broadcast circuit broadcasts at 300 m band. A condenser of capacitance 2.4 lµF is available. The value of the inductance required for resonant circuit is
(a) 10-4 H
(b) 10-8 H
(c) 10-6 H
(d) 10-2 H

In parallel resonant circuit
(a) impedance is very high
(b) current is very high
(c) voltage is very high
(d) None of these

Answer: (a) impedance is very high

Transformer works on the principle of
(a) convertor
(b) invertor
(c) mutual induction
(d) self-induction

In a pure capacitive circuit if the frequency of ac source is doubled, then its capacitive reactance will be
(a) remains same
(b) doubled
(c) halved
(d) zero

In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply. Which of the following elements are likely to constitute the circuit?
(a) Only resistor
(b) Resistor and inductor
(c) Resistor and capacitor
(d) Only inductor

In a series LCR circuit the voltage across an inductor, capacitor and resistor are 20 V, 20 V and 40 V respectively. The phase difference between the applied voltage and the current in the circuit is
(a) 30°
(b) 45°
(c) 60°
(d) 0°

The frequency of A.C. mains in India is
(a) 30 c/s
(b) 50 c/s
(c) 60 c/s
(d) 120 c/s

The electric mains supply in our homes and offices is a voltage that varies like a sine function with time such a voltage is called … A… and the current driven by it in a circuit is called the … B… Here, A and B refer to
(a) DC voltage, AC current
(b) AC voltage, DC current
(c) AC voltage, DC voltage
(d) AC voltage, AC current

Answer: (d) AC voltage, AC current

The peak value of the a.c. current flowing throw a resistor is given by
(a) I0 = e0/R
(b) I = e/R
(c) I0= e0
(d) I0 = R/e0

Alternating current can not be measured by D.C. ammeter, because
(a) A. C. is virtual
(b) A. C. changes its direction
(c) A. C. can not pass through D.C. ammeter
(d) average value of A. C for complete cycle is zero

Answer: (d) average value of A. C for complete cycle is zero

Phase difference between voltage and current in a capacitor in an ac circuit is
(a) π
(b) π/2
(c) 0
(d) π/3

A capacitor has capacitance C and reactance X, if capacitance and frequency become double, then reactance will be
(a) 4X
(b) X/2
(c) X/4
(d) 2X

If an LCR series circuit is connected to an ac source, then at resonance the voltage across
(a) R is zero
(b) R equals the applied voltage
(c) C is zero
(d) L equals the applied voltage

Answer: (b) R equals the applied voltage

(a) depends on the amount of the electrolyte
(b) depends on the current in the electrolyte
(c) is a universal constant
(d) depends on the amount of charge passed through the electrolyte

Answer: (c) is a universal constant

If an AC voltage is applied to an ICi? circuit, which of the following is true?
(a) I and V are out of phase with each other inR
(b) I and V are in phase in L while in C, they are out of phase
(c) I and V are out of phase in both C and L
(d) I and V are out of phase in L and in phase in C

Answer: (c) I and V are out of phase in both C and L

In an LCR circuit, capacitance is charged from C to 2C. For resonant frequency to remain unchanged, the inductance should be changed from L to
(a) 4 L
(b) 2 L
(c) L/2
(d) L/4

For an ideal-step-down transformer, the quantity which is constant for both the coils is
(a) current in the coils
(b) voltage across the coils
(c) resistance of coils
(d) power in the coils

Answer: (d) power in the coils

Quality factor and power factor both have the dimensions of
(a) time
(b) frequency
(c) work
(d) angle

An electric circuit containing capacitor only suffers
(a) equal resistance for A.C. and D.C.
(b) Resistance of A.C. > Resistance of D.C.
(c) Resistance for A.C. < Resistance of D.C.
(d) offers infinite resistance for D.C.

Answer: (d) offers infinite resistance for D.C.

Two coils X and Y are connected in series across a 240 V, 50 Hz supply. The resistance of X is 5Ω and inductance of Y is 0.02 H. The power consumed is 3 kW and the power factor is 0.75. The impedance of the circuit is
(a) 0.144 Ω
(b) 1.44 Ω
(c) 14.4 Ω
(d) 144 Ω

At resonance frequency the impedance in series LCR circuit is
(a) maximum
(b) minimum
(c) zero
(d) infinity

The current through an inductor of 1H is given by I = 3t sin t. The voltage across the inductor of 1 H is
(a) 3 sin t + 3 cos t
(b) 3 sin t + 3t cos t
(c) 3 cos t + t sin t
(d) 3t cos t + sin t

Answer: (b) 3 sin t + 3t cos t

The inductive reactance of an inductor coil of 1/π H at 50 Hz is
(a) 50/π Ω
(b) π/50 Ω
(c) 100 Ω
(d) 50 Ω