# CBSE Class 12 Physics Alternating Current Important Questions Worksheet Set B

Read and download free pdf of CBSE Class 12 Physics Alternating Current Important Questions Worksheet Set B. Students and teachers of Class 12 Physics can get free printable Worksheets for Class 12 Physics in PDF format prepared as per the latest syllabus and examination pattern in your schools. Standard 12 students should practice questions and answers given here for Physics in Grade 12 which will help them to improve your knowledge of all important chapters and its topics. Students should also download free pdf of Class 12 Physics Worksheets prepared by school teachers as per the latest NCERT, CBSE, KVS books and syllabus issued this academic year and solve important problems provided here with solutions on daily basis to get more score in school exams and tests

## Alternating Current Important Questions Class 12 Physics Worksheet Pdf

Class 12 Physics students should refer to the following printable worksheet in Pdf for Alternating Current Important Questions in standard 12. This test paper with questions and answers for Grade 12 Physics will be very useful for exams and help you to score good marks

### Class 12 Physics Worksheet for Alternating Current Important Questions

CBSE Class 12 Physics Current Electricity Important Questions (1). Students can download these worksheets and practice them. This will help them to get better marks in examinations. Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

1 What is an alternating voltage? Give an equation to represent the same.

2 Explain how a resistor responds to an alternating voltage with relevant equations. Give the graphical representations of current and voltage across the resistor.

3 Define mean value of current and derive the relation between the peak value of current and mean value of current. What is the value of average power consumed in a complete cycle?

4 Define the rms value of current. Derive the relation between the peak value and rms value of current.

5 A light bulb is rated at 100 W for a 220 V supply. Find (a) the resistance of the bulb ;

(b) the peak voltage of the source; and (c) the rms current through the bulb.

6 What is a phasor? Give the phasor diagram showing the voltage and current phasors and their relationship at time t in case of an ac source connected to a resistor.

7 Explain how an inductor responds to an alternating voltage with relevant equations. Give the phasor diagram for the same.

8 Show that the average power through an ac circuit consisting of inductor over one complete cycle is zero.

9 A pure inductor of 25 mH is connected to a source of 220 V. Find the inductive reactance and rms current in the circuit if the frequency of the source is 50 Hz.

10 Give the formula to find the reactance due to an inductor. What is the function of reactance in a circuit? What is the relationship between the current and voltage when alternating current is allowed to flow through an ac circuit? Explain

11 Explain what happens to ac current when it is allowed to flow through a circuit consisting of a capacitor. What is the phase relationship between the current and voltage?

Important Questions for NCERT Class 12 Physics Alternating Current

Question. If we decrease the frequency of the applied A.C. with a purely capacitive load, do (1) the amplitude of Vc and (2) amplitude of Ic increase, decrease of remain the same.

(a) (1) increase (2) same
(b) (1) same (2) increase
(c) (1) same (2) decrease
(d) (1) decrease (2) same

Question. An inductor coil of inductance L is cut into two equal parts and both the parts are connected in parallel. The net inductance is :
(a) L
(b) L/2
(c) L/4
(d) 2 L.

Question. An inductance L having a resistance R is connected to an alternating source of angular frequency w. The Quality factor Q of inductance is
(a) R/ wL
(b) (wL/R)2
(c) (R /wL)1/2
(d) wL/R

Question. In an A.C. circuit, the current flowing in inductance is I = 5 sin (100 t – p/2) amperes and the potential difference is V = 200 sin (100 t) volts. The power consumption is equal to
(a) 1000 watt
(b) 40 watt
(c) 20 watt
(d) zero

Question. L, C, R represent physical quantities inductance, capacitance and resistance respectively. The combinations which have the dimensions of frequency are
(a) 1/RC
(b) R/L
(c) 1/ LC
(d) C/L

Question. An inductance L having a resistance R is connected to an alternating source of angular frequency w. The Quality factor Q of inductance is
(a) R/ wL
(b) (wL/R)2
(c) (R /wL)½
(d) wL/R

Question. A step down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in the primary coil will be
(a) 1600 amp
(b) 20 amp
(c) 4 amp
(d) 1.5 amp

Question. The mutual inductance of a pair of coils, each of N turns, is M henry. If a current of I ampere in one of the coils is brought to zero in t second, the emf induced per turn in the other coil, in volt, will be
(a) MI /t
(b) NMI /t
(c) MN /It
(d) MI /Nt

Question. An A.C. circuit containing only capacitance, the current :
(a) lags the voltage by 90°
(b) leads the voltage by 90°
(c) remains in phase with voltage
(d) leads the voltage in 180°

Question. A choke coil has:
(a) Low inductance and low resistance
(b) High inductance and high resistance
(c) Low inductance and high resistance
(d) High inductance and low resistance

Question. The tuning circuit of a radio receiver has a resistance of 50W, an inductor of 10 mH and a variable capacitor. A 1 MHz radio wave produces a potential difference of 0.1 mV. The values of the capacitor to produce resonance is (Take Π2 = 10)
(a) 2.5 pF
(b) 5.0 pF
(c) 25 pF
(d) 50 pF

Question. A coil has resistance 30 ohm and inductive reactance 20 ohm at 50 Hz frequency. If an ac source, of 200 volt, 100 Hz, is connected across the coil, the current in the coil will be
(a) 4.0 A
(b) 8.0 A
(c) 20√13 A
(d) 2.0 A

Question. The primary winding of a transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an A.C. supply of 20 V, 50 Hz. The secondary will have an output of
(a) 2 V, 50 Hz
(b) 2 V, 5 Hz
(c) 200 V, 50 Hz
(d) 200 V, 500 Hz.

Question. A coil of 40 henry inductance is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is
(a) 5 seconds
(b) 1/5 seconds
(c) 40 seconds
(d) 20 seconds

Question. An ideal coil of 10H is connected in series with a resistance of 5W and a battery of 5V. After 2 sec the connection is made, the current flowing in ampere in the circuit is
(a) (1 – e–1)
(b) (1 – e)
(c) e
(d) e–1

Question. An inductor, a resistor and a capacitor are joined in series with an AC source. As the frequency of the source is slightly increased from a very low value, the reactance of the
(a) inductor increases
(b) resistor increases
(c) capacitor increases
(d) circuit increases

Question. In an A.C. circuit, Irms and I0 are related as
(a) Irms = ΠI0
(b) Irms = √2 I0
(c) Irms = I0/Π
(d) Irms = I0 /√ 2

Question. Two cables of copper are of equal lengths. One of them has a single wire of area of cross-section A, while other has 10 wires of cross-sectional area A/10 each. Give their suitability for transporting A.C. and D.C.
(a) only multiple strands for A.C., either for D.C.
(b) only multiple strands for A.C., only single strand for D.C.
(c) only single strand for D.C., either for A.C.
(d) only single strand for A.C., either for D.C.

Question. A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when
(a) a capacitance of reactance XC = XL is included in the same circuit.
(b) an iron rod is inserted in the coil.
(c) frequency of the AC source is decreased.
(d) number of turns in the coil is reduced.

Question. In an ac circuit an alternating voltage 200 2 sin100 t volts is connected to a capacitor of capacity 1 mF. The r.m.s. value of the current in the circuit is
(a) 10 mA
(b) 100 mA
(c) 200 mA
(d) 20 mA

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