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Alternating current MCQs for competition exam.

 1) Which of the following show alternating E.M.F?:-

A) E = E₀Sinωt

B) E = E₀Cosωt

C) E = E₀tanωt

D) E = E₀cotωt

Ans:- A) E = E₀Sinωt


2) An alternating e.m.f is one which:-

A) changes direction continuously but not magnitude.

B) continuously flow in one direction.

C) continuously changes in magnitude and periodically reverse in direction.

D) None of the above.

Ans:- C) continuously changes in magnitude and periodically reverse in direction.


3) Time period of the alternating current is given by:-

A) T = 4π/ω

B) T = 2π²/ω

C) T = 2πr/ω

D) T = 2π/ω

(where ω = angular frequency of a.c.)

Ans:- D) T = 2π/ω


4) Frequency of the alternating current is given by:-

A) f = ω²/2π

B) f = 2π/ω

C) f = ω/2π

D) None of the above.

Ans:- C) f = ω/2π


5) Mean value of a.c is also called:-

A) maximum value of a.c.

B) D.C value of a.c.

C) minimum value of a.c.

D) peak value of a.c.

Ans:- B) D.C value of a.c.


6) Root mean square value of a.c is also called:-

A) virtual value of a.c.

B) average value of a.c.

C) peak value of a.c.

D) minimum value of a.c.

Ans:- A) virtual value of a.c.


7) The average value of a.c. taken over the complete cycle of a.c current is equal to:-

A) 1

B) -1

C) ∞

D) 0

Ans:- D) 0


8) Which of the following equation express the a.c current?:-

A) i = I₀tanωt

B) i = I₀sinωt

C) i = sinωt

D) i = I₀sinω

Ans:- B) i = I₀sinωt


9) Relation between root mean square value of alternating current and peak value of a.c current is given by:-

A) Iᵥ = I₀√2

B) Iᵥ = I₀/√2

C) Iᵥ = √2/I₀

D) Iᵥ = I₀²/√2

Ans:- B) Iᵥ = I₀/√2


10) The relation between root mean square value of e.m.f and peak value of e.m.f is given by :-

A) Eᵥ = E₀/√7

B) Eᵥ = E₀/√3

C) Eᵥ = √2/E₀

D) Eᵥ = E₀/√2

Ans:- D) Eᵥ = E₀/√2


11) Inductance in an a.c circuit is due to :-

A) induced e.m.f.

B) collision of electrons.

C) temperature difference.

D) None of the above.

Ans:- A) induced e.m.f.


12) Which of the following equation gives  the Inductance of an a.c. circuit:-

A) Xₗ = ωL²/2

B) Xₗ = ω²L

C) Xₗ =1/ωL

D) Xₗ = ωL

Ans:- D) Xₗ = ωL


13) Capacitance of an a.c circuit is given by:-

A) Xᵦ = ωC/2

B) Xᵦ = 1/ωC

C) Xᵦ = ωL

D) Xᵦ = ω²C

(where C = capacity of condenser)

Ans:- B) Xᵦ = 1/ωC


14) Impedance is the combining effect of:-

A) inductance and capacitance.

B) resistance and capacitance.

C) resistance, inductance and capacitance.

D) resistance and inductance.

Ans:- C) resistance, inductance and capacitance.


15) A transformer is used in :-

A) D.C. supply only.

B) a.c. supply only.

C) both a.c. and d.c. supply.

D) None of the above.

Ans:- B) a.c. supply only.


16) A transformer is used to change :-

A) high voltage a.c. into low voltage a.c.

B) high voltage d.c. into low voltage d.c.

C) mechanical energy into electrical energy.

D) electrical energy into mechanical energy.

Ans:- A) high voltage a.c. into low voltage a.c.


17) The current in resistance R at resonance is :-

A) zero.

B) infinite.

C) maximum but finite.

D) minimum but finite.

Ans:- C) maximum but finite.


18) A choke coil is a coil with :-

A) low inductance and high resistance.

B) high inductance and negligible small resistance.

C) high inductance and high resistance.

D) low inductance and low resistance.

Ans:- B) high inductance and negligible small resistance.


19) When a fluorescent tube is used in a.c. circuit :-

A) a choke is connected in parallel.

B) a resistance is connected in series.

C) a choke is connected in series.

D) None of the above.

Ans:- C) a choke is connected in series.


20) Power factor of an a.c. circuit is given by :-

A) cosø = (true power)/apparent power

B) cosØ = (apparent power)/true power

C) cosø = true power × apparent power

D) None of the above.

Ans:- A) cosø = (true power)/apparent power


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