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Published on: 13/10/2020
12th Standard Physics Electromagnetic Induction and Alternating Current English Medium Free Online Test One Mark questions with Answer Key 2020 - 2021
Download Tamil Nadu 12th Standard Physics question papers, model tests, one-mark questions, important questions, and public exam papers in PDF format. Free study materials and answer keys for TN State Board students.
Questions + Answers key
Take MCQ Physics Test1.
The instantaneous current in an AC circuit containing a pure inductor is i = Io sinωt, The instantaneous emf is ___________________.
e = Eosin\(\left( \omega t+\frac { \pi }{ 2 } \right) \)
e = Eosin\(\left( \omega t-\frac { \pi }{ 2 } \right) \)
e=Eosin(ωt - π)
e = Eosin
2.
The power factor of an a.c, circuit is _________
\(\phi \)sin\(\phi \)
cosec \(\phi \)
cos \(\phi \)
tan \(\phi \)
3.
Unit of inductive reactance is ___________
ohm-metre
mho-metre-1
ohm
mho
4.
The voltage drop across the resistor in a LCR series circuit is __________________
VR = IR
VR = IR2
VR = I/R
VR=R/I
5.
The efficiency of an ideal transformer is ____________.
0
1
infinite
none
6.
__________ principle is used in transformer.
mutual induction
electromagnetic induction
self induction
eddy currents
7.
In an a.c. dynamo, the induced current is _________ in nature.
alternating
increasing
decreasing
constant
8.
In an a.c generator, the brushes are made of __________
silicon
plastic
carbon
nylon
9.
The property of a coil which enables to produce an opposite induced emf in it when the current in the coil changes is called _______________
electromagnetism
self - induction
mutual induction
parallel- induction
10.
A phenomenon in which a varying current in one coil induces an emf in the neighbouring coil is ___________.
mutual induction
self induction
electrostatic induction
electromagnetic induction
11.
The unit of self inductance is ________________.
Henry
Ampere
Farad
Ohm
12.
If a secondary coil has 40 turns, and a primary coil with 20 turns is charged with 50V of potential difference, then potential difference in secondary would be ________________.
50 V
25 V
60 V
100 V
13.
Which of the following cannot be stepped up in a transformer?
input current
input voltage
input power
all
14.
An emf of 12V is induced when the current in the coil changes at the rate of 40 A S-1. The coefficient of self-induction of the coil is _______________.
0.3 H
0.003 H
30 H
4.8 H
15.
The self-inductance of a straight conductor is ________________.
zero
infinity
very large
very small
16.
Lenz's law is in accordance with the law of ________________.
conservation of charges
conservation of flux
conservation of momentum
conservation of energy
17.
An inductor 20 mH, a capacitor 50 μF and a resistor 40Ω are connected in series across a source of emf V = 10 sin 340 t. The power loss in AC circuit is
0.76 W
0.89 W
0.46 W
0.67 W
18.
In a series RL circuit, the resistance and inductive reactance are the same. Then the phase difference between the voltage and current in the circuit is
\(\frac{\pi}{4}\)
\(\frac{\pi}{2}\)
\(\frac{\pi}{6}\)
zero
19.
A circular coil with a cross-sectional area of 4 cm2 has 10 turns. It is placed at the centre of a long solenoid that has 15 turns/cm and a cross-sectional area of 10 cm2. The axis of the coil coincides with the axis of the solenoid. What is their mutual inductance?
7.54 μH
8.54 μH
9.54 μH
10.54 μH
20.
When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. The co-efficient of self-induction of the coil is
0.2H
0.4H
0.8H
0.1H
1.
(a)
e = Eosin\(\left( \omega t+\frac { \pi }{ 2 } \right) \)
2.
(c)
cos \(\phi \)
3.
(c)
ohm
4.
(a)
VR = IR
5.
(b)
1
6.
(b)
electromagnetic induction
7.
(a)
alternating
8.
(c)
carbon
9.
(b)
self - induction
10.
(a)
mutual induction
11.
(a)
Henry
12.
(d)
100 V
13.
(c)
input power
14.
(a)
0.3 H
15.
(a)
zero
16.
(d)
conservation of energy
17.
L = 20 x 10-3H. C = 50 x 10-6 F, R= 40Ω
enf V = 10 sin 340 t
\(\therefore V_0=10 \mathrm{~V}, \omega=340 \)
\(X_1=1 \omega^{\prime}=20 \times 10^3 \times 340 \)
\(=6800 \times 10^{-1}=6.8 \Omega \)
\(X_C=\frac{1}{C .} \)
\(=\frac{1}{50 \times 10^{-\alpha} \times 340}=\frac{10^{\circ}}{17000}=\frac{10^{\prime}}{17}=58.823 \Omega \)
\(Z=\sqrt{R^2+\left(X_6-X_1\right)^2} \)
\(=\sqrt{(40)^2+(58.82-6.8)^2} \)
\(=\sqrt{(40)^2+(52.02)^2} \)
\(=65.62 \Omega\)
The peak current in the circuit is,
\(I_0=\frac{V_0}{Z}=\frac{10}{65.62} \)
\(\cos 0=\frac{R}{Z}=\frac{40}{65.62} \)
\(\text{Power loss in A.C. circuit }=V_{r m} 1_{r \rightarrow \infty} \cos \phi \)
\(=\frac{1}{2} V_{\mathrm{o}} I_{\mathrm{c}} \cos \phi \)
\(=\frac{1}{2} \times 10 \times \frac{10}{65.62} \times \frac{40}{65.62}\)
\(\frac{2000}{4305.98}\)
= 0.46 W
18.
In RL circuit, tanΦ = \(\frac{X_l}{R}\)
If R = X1, then tanΦ = \(\frac{X_l}{X_l}=1\)
∴ Φ = tan-1(1)=\(\frac{\pi}{4}\)
∴ Phase difference \(=\frac{\pi}{4}\)
19.
\(A_1 =4 \times 10^{-4} \mathrm{~m}^2 \)
\(N_1 =10 \text { turns } \)
\(A_2 =4 \times 10^{-4} \mathrm{~m}^2 \)
\(N_2 =15 \times 10^{-}=1500 \mathrm{turn} / \mathrm{m} \)
\(\phi =B_2 A_2=\left(\mu_0 \mathrm{n}_2 I_2\right) \mathrm{A}_1 \)
\(Where, \mathrm{n}_2=\frac{\mathrm{N}_2}{l}=1500 \mathrm{turn} / \mathrm{m}\)
The mutual Inductance is,
\(M =\frac{N_1 o_{12}}{I_2}=\mu_0 n_2 N_1 A_1 \)
\(=4 \pi \times 10^{-7} \times 1500 \times 10 \times 4 \times 10^{-4} \)
\(=7.54 \times 10^{-6} \mathrm{H}=7.54 \mu \mathrm{H}\)
20.
\(\text {emf } e=8 \mathrm{~V} \)
\(d I=I_1-I_0=2-(-2)=4 \mathrm{~A} \)
\(\text {dt }=0.05 \mathrm{~s} \)
\(L=\frac{-e}{d I / d t}=\frac{-8}{4 / 0.05} \)
\(=\frac{-8 \times 0.05}{4}=\frac{-0.40}{4} \)
=-0.1 H
-ve sign indicates that self-induced emf always opposes the current w.r.t. time.
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