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12th Physics weekly Test -2 ( Electromagnetic Induction And Alternating Current)

St. Britto Hr. Sec. School - Madurai

12th Physics weekly Test -2 ( Electromagnetic Induction And Alternating Current)-Aug 2020

Time : 1.30 Hours

Part - A

Multiple Choice Question - Answer All Question

In a series resonant RLC circuit, the voltage across 100 Ω resistor is 40 V. The resonant frequency ω is 250 rad/s. If the value of C is 4 μF, then the voltage across L is

600 V
4000 V
400 V
1 V

AC generator works on the principle of

self induction
mutual induction
electromagnetic induction
none of these

In an electrical circuit, R, L, C and AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and current in the circuit is \(\frac{\pi}{3}\). Instead, if C is removed from the circuit, the phase difference is again \(\frac{\pi}{3}\). The power factor of the circuit is

1/2
1/\(\sqrt2\)
1
\(\sqrt3\)/2

The quantity that changes with time in an A.C current is

magnitude
direction
both magnitude and direction
none

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

A step-down transformer reduces the supply voltage from 220 V to 11 V and increase the current from 6 A to 100 A. Then its efficiency is

1.2
0.83
0.12
0.9

The generator rule is

Fleming's left hand rule
Fleming's right hand rule
Maxwell's right hand cork screw rule
Right hand palm rule

The reactance of a capacitor is,

X_c= Cω
X_c = \(\frac{1}{Cω}\)
X_c = \(\frac{C}{ω}\)
X_c = \(\frac{ω}{C}\)

Lenz's law is in accordance with the law of

conservation of charges
conservation of flux
conservation of momentum
conservation of energy

__________ principle is used in transformer.

mutual induction
electromagnetic induction
self induction
eddy currents

In a LCR series a.c, circuit, the phase difference between current and voltage is 60°. If the net reactance of the circuit is 17.32Ω, the value of the resistance is

30Ω
17.32 Ω
10 Ω
1.732 Ω

In an oscillating LC circuit, the maximum charge on the capacitor is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic fields is

\(\frac{Q}{2}\)
\(\frac{Q}{\sqrt3}\)
\(\frac{Q}{\sqrt2}\)
Q

The power factor of an a.c, circuit is _________

\(\phi \)sin\(\phi \)
cosec \(\phi \)
cos \(\phi \)
tan \(\phi \)

The unit of impedance is ________________

mho-metre^-1
ohm
ohm-metre
mho-metre

In a transformer, eddy current loss is minimized by using

laminated core made of muemetal
laminated core made of stelloy
shell type core
thick copper wire

When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. Th e co-efficient of self-induction of the coil is

0.2H
0.4H
0.8H
0.1H

The phase difference between VL and Vc is _________________

2π
π/2
π/4
π

The formula for calculating the power loss in a power line is _____________

P = I²R
P=IR
P=IR²
P=I²R²

The instantaneous values of alternating current and voltage in a circuit are \(i=\frac { 1 }{ \sqrt { 2 } } sin\left( 100\pi t \right) \) A and v=\(=\frac { 1 }{ \sqrt { 2 } } sin\left( 100\pi t+\frac { \pi }{ 3 } \right) V.\)The average power in watts consumed in the circuit is

\(\frac{1}{4}\)
\(\frac{\sqrt3}{4}\)
\(\frac{1}{2}\)
\(\frac{1}{8}\)

The necessary magnetic field for a low power a.c generator is produced by _________

electric coil
permanent magnets
electromagnets
batteries

Part - B

Generic 5 - Answer All Question

Draw graphs showing the distribution of charge in a capacitor and current through an inductor during LC oscillations with respect to time. Assume that the charge in the capacitor is maximum initially.

Derive a relation between mean or average value of AC and its peak value.

A circular coil of radius 10cm) 500 turns and resistance 2Ω is placed with its plane perpendicular to the horizontal component of the earth's magnetic field it is rotated about its vertical diameter through 180° in 0-25 S estimate the magnitude of the emf and current induced in the coil. Horizontal component of earth's magnetic field at the place is 3 x 10^-5T.

A fan of metal blades of length 0.4 m rotates normal to a magnetic field of 4 x 10^-3T. If the induced emf between the centre and edge of the blade is 0.02 V, determine the rate of rotation of the blade.

Derive an expression for the RMS value of AC.

A rectangular coil of area 70 cm² having 600 turns rotates about an axis perpendicular to a magnetic field of 0.4 Wb m-2. If the coil completes 500 revolutions in a minute, calculate the instantaneous emf when the plane of the coil is
(i) perpendicular to the field
(ii) parallel to the field and
(iii) inclined at 60o with the field.

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