## Alternating Current

**Class 12 Physics Chapter 7 Objective in English :** Here you can find class 12th physics Objective questions for board exam 2024. **Alternating Current **objective questions is very important for board exam 2023 – 2024. mcq questions for class 12 physics chapter 7 in English. important question website

## 12th Physics Chapter 7 Objective Questions in English

**Alternating voltage (V) is represented by the equation**

(A) V(t) = Vm eωt

(B) V(t) = Vm sin ωt

(C) V(t) = Vm cot ωt

(D) V(t) = Vm tan ωt

**In the case of an inductor**

(A) voltage lags the current by π/2

(B) voltage leads the current by π/2

(C) voltage leads the current by π/3

(D) voltage leads the current by π/4

**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 which of the following circuits the maximum power dissipation is observed?**

(A) Pure capacitive circuit

(B) Pure inductive circuit

(C) Pure resistive circuit

(D) None of these

**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°

**At resonance frequency the impedance in series LCR circuit is**

(A) maximum

(B) minimum

(C) zero

(D) infinity

**At resonant frequency the current amplitude in series LCR circuit is**

(A) maximum

(B) minimum

(C) zero

(D) infinity

**Quality factor and power factor both have the dimensions of**

(A) time

(B) frequency

(C) work

(D) angle

**A transformer works on the principle of**

(A) self induction

(B) electrical inertia

(C) mutual induction

(D) magnetic effect of the electrical current

**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

**In an LCR series ac circuit, the voltage across each of the components L, C and R is 50 Volt. The voltage across LC combination is :**

(A) 50 Volt

(B) 25 Volt

(C) 100 Volt

(D) 0 Volt

**The phase difference between current and voltage in an AC circuit is θ. Then power factor will be:**

(A) cosθ

(B) sinθ

(C) Tanθ

(D) Cotθ

**The working principle of choke coil is based on**

(A) Conservation of angular momentum

(B) Self induction

(C) Mutual induction

(D) Conservation of momentum

**In a step up transformer the number of coils in primary coils is****and****in secondary. Then :-**

(A) N_{1} = N_{2}

(B) N_{1} < N_{2}

(C) N_{1} > N_{2}

(D) None of these

**The device that increases AC voltage is called –**

**(A) resistor**

**(B) step-down transformer **

**(C) step-up transformer**

**(D) transformer**

**The oscillation frequency of an LC circuit is f. If both the capacitance and inductance be doubled, the frequency will become –**

**(A) f / 4**

**(B) 2f**

**(C) 4f**

**(D) f / 2**

**In LCR-circuit, L = 8.0 H, C = 0.5 μF, and R = 100 Ω are connected in series. The resonant frequency will be**

(A) 600 radian/second

(B) 500 radian/second

(C) 600 hertz

(D) 500 hertz

**A choke coil is used to control current in a circuit of**

(A) ac only

(B) dc only

(C) both ac and dc

(D) None of these

**Step-down transformer increases**

(A) current

(B) voltage

(C) wattage

(D) None of these

**The thermal effect of alternating current is practically**

(A) Joule heating

(B) Peltier heating

(C) Thomson effect

(D) None of these

**The power factor of a choke coil is about**

(A) 90°

(B) 0

(C) 1

(D) 180°

**The power factor of a condenser is**

(A) 90°

(B) 1

(C) 180°

(D) 0

**For which of the following, capacitor works as infinite resistance ?**

(A) DC

(B) AC

(C) both DC and AC

(D) None of these

**L-C circuit without AC-source is called**

(A) oscillatory circuit

(B) drift circuit

(C) hysteresis circuit

(D) None of these

**The unit of Impedance is**

(A) henry

(B) ohm

(C) tesla

(D) None of these

**The equation of an AC is I = 60sin100πt 60sin100πt. The root mean square value will be**

(A) 60√2

(B) 60 /√2

(C) 100

(D) zero

**The value of phase difference between current and emf in an AC circuit with resistance only, is –**

(A) zero

(B) π / 2

(C) π

(D) 2π

**A 60 μF capacitor is connected to a 110 V (rms), 60 Hz ac supply. The rms value of current in the circuit is**

(A) 1.49 A

(B) 14.9 A

(C) 2.49 A

(D) 24.9 A

**The peak voltage of an ac supply is 440 V, then its rms voltage is**

(A) 31.11 V

(B) 311.1 V

(C) 41.11V

(D) 411.1V

**The rms value of current in an ac circuit is 25 A, then peak current is**

(A) 35.36 mA

(B) 35.36 A

(C) 3.536 A

(D) 49.38 A

**A light bulb is rated at 100 W for a 220 V ac supply. The resistance of the bulb is**

(A) 284 Ω

(B) 384 Ω

(C) 484 Ω

(D) 584 Ω

**A 44 mH inductor is connected to 220 V, 50 Hz ac supply. The rms value of the current in the circuit is –**

(A) 12.8 A

(B) 13.6 A

(C) 15.9 A

(D) 19.5 A

**A 30 μF capacitor is connected to a 150 V, 60 Hz ac supply. The rms value of current in the circuit is –**

(A) 17 A

(B) 1.7 A

(C) 1.7 mA

(D) 2.7 A

**The resonant frequency of a series LCR circuit with L = 2.0 H, C = 32 μF and R = 10 Ω is**

(A) 20 Hz

(B) 30 Hz

(C) 40 Hz

(D) 50 Hz