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

Answer: (c) R only

**What is the ratio of inductive and capacitance reactances in an ac circuit?**(a) 1

(b) ω²L

(c) ω²LC

(d) l

Answer: (c) ω²LC

**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

Answer: (b) 10-8 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

Answer: (c) mutual 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

Answer: (c) halved

**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

Answer: (c) Resistor and capacitor

**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°

Answer: (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

Answer: (b) 50 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) I_{0} = e_{0}/R

(b) I = e/R

(c) I_{0}= e_{0}

(d) I_{0} = R/e_{0}

Answer: (a) I0 = e0/R

**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

Answer: (b) π/2

**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

Answer: (c) X/4

**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

**Faraday constant**(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

Answer: (c) L/2

**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

Answer: (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

Answer: (c) 14.4 Ω

**At resonance frequency the impedance in series LCR circuit is**(a) maximum

(b) minimum

(c) zero

(d) infinity

Answer: (b) minimum

**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

Answer: (c) 100 Ω

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