Electromagnetic Induction And Alternating Current Practice Test

12th Standard Physics — Electromagnetic Induction And Alternating Current: Online Practice Test

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An electron moves on a straight line path XY as shown in the figure. The coil abcd is adjacent to the path of the electron. What will be the direction of current, if any, induced in the coil?

An electron moves along a straight line XY near a rectangular conducting loop abcd.

A.The current will reverse its direction as the electron goes past the coil B.No current will be induced C.abcd D.adcb

A thin semi-circular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure. The potential difference developed across the ring when its speed v, is

A semicircular conducting loop PQR falls through a uniform horizontal magnetic field B.

A.Zero B.\(B \pi rv^2/2\) and P is at higher potential C.\(\pi rBv\) and R is at higher potential D.\(2rBv\) and R is at higher potential

The flux linked with a coil at any instant t is given by \(\Phi_B = 10t^2 - 50t + 250\). The induced emf at t = 3 s is

A.-190 V B.-10 V C.10 V D.190 V

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

A.0.2 H B.0.4 H C.0.8 H D.0.1 H

The current i flowing in a coil varies with time as shown in the figure. The variation of induced emf with time would be

A primary graph showing current variation with time and four optional graphs showing the resulting induced emf.

A.A

B.B

C.C

D.D

A circular coil with a cross-sectional area of 4 cm\(^2\) 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 cm\(^2\). The axis of the coil coincides with the axis of the solenoid. What is their mutual inductance?

A.7.54 \(\mu\)H B.8.54 \(\mu\)H C.9.54 \(\mu\)H D.10.54 \(\mu\)H

In a transformer, the number of turns in the primary and the secondary are 410 and 1230 respectively. If the current in primary is 6A, then that in the secondary coil is

A.2 A B.18 A C.12 A D.1 A

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

A.1.2 B.0.83 C.0.12 D.0.9

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 \(\pi/3\). Instead, if C is removed from the circuit, the phase difference is again \(\pi/3\). The power factor of the circuit is

A.1/2 B.\(1/\sqrt{2}\) C.1 D.\(\sqrt{3}/2\)

Q10

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

A.\(\pi/4\) B.\(\pi/2\) C.\(\pi/6\) D.zero

Q11

In a series resonant RLC circuit, the voltage across 100 \(\Omega\) resistor is 40 V. The resonant frequency \(\omega\) is 250 rad/s. If the value of C is 4 \(\mu\)F, then the voltage across L is

A.600 V B.4000 V C.400 V D.1 V

Q12

An inductor 20 mH, a capacitor 50 \(\mu\)F and a resistor 40 \(\Omega\) are connected in series across a source of emf V = 10 sin 340 t. The power loss in AC circuit is

A.0.76 W B.0.89 W C.0.46 W D.0.67 W

Q13

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

A.1/4 B.3/4 C.1/2 D.1/8

Q14

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

A.\(Q/2\) B.\(Q/\sqrt{3}\) C.\(Q/\sqrt{2}\) D.Q

Q15

\(\frac{20}{\pi^2}\) H inductor is connected to a capacitor of capacitance C. The value of C in order to impart maximum power at 50 Hz is

A.50 \(\mu\)F B.0.5 \(\mu\)F C.500 \(\mu\)F D.5 \(\mu\)F

Q16

A rectangular loop of area A is placed in a uniform magnetic field B. If the angle between the magnetic field direction and the plane of the loop is 30 degrees, what is the magnetic flux linked with the loop?

A.BA B.BA / 2 C.(sqrt(3) * BA) / 2 D.Zero

Q17

According to Lenz's law, the induced current in a circuit always flows in a direction such that its own magnetic field opposes:

A.the existing magnetic flux B.the external magnetic field C.the change in magnetic flux D.the electromotive force

Q18

To minimize power loss due to eddy currents in the core of a transformer, the core is typically:

A.made of a single solid block of soft iron B.constructed from thin, insulated laminations C.cooled to cryogenic temperatures D.made of a non-magnetic material

Q19

The self-inductance of a long solenoid of length l, area A, and total number of turns N in vacuum is given by:

A.(mu_0 * N^2 * A) / l B.mu_0 * N * A * l C.(mu_0 * N * A) / l D.mu_0 * N^2 * A * l

Q20

Two neighboring coils have a mutual inductance of 2 H. If the current in the first coil changes at a constant rate of 5 A/s, the magnitude of the induced emf in the second coil is:

A.2.5 V B.5 V C.10 V D.20 V

Q21

A metal rod of length L moves with a constant velocity v perpendicular to a uniform magnetic field B. The induced motional emf across its ends is:

A.BLv B.0.5 * BLv C.BLv^2 D.B^2Lv

Q22

In a single-phase AC generator, the induced emf is at its maximum value when the plane of the rotating coil is:

A.perpendicular to the magnetic field lines B.parallel to the magnetic field lines C.inclined at 45 degrees to the field lines D.stationary within the field

Q23

In an ideal step-up transformer, which of the following is true when comparing the secondary to the primary?

A.The secondary voltage is higher and current is higher B.The secondary voltage is lower and current is lower C.The secondary voltage is higher and current is lower D.The secondary voltage is lower and current is higher

Q24

The root mean square (RMS) value of a sinusoidal alternating current with a peak value Im is:

A.Im / 2 B.Im / sqrt(2) C.sqrt(2) * Im D.2 * Im

Q25

In an AC circuit consisting of a pure inductor, the current:

A.leads the voltage by 90 degrees B.lags the voltage by 90 degrees C.is in phase with the voltage D.leads the voltage by 180 degrees

Q26

If the frequency of the AC source in a purely capacitive circuit is tripled, the capacitive reactance Xc becomes:

A.three times its original value B.nine times its original value C.one-third of its original value D.unchanged

Q27

In a series RLC circuit, electrical resonance occurs when the frequency of the source is such that:

A.The resistance is zero B.Inductive reactance is equal to capacitive reactance C.The impedance is at its maximum value D.The current is at its minimum value

Q28

The power factor of an AC circuit is defined as the cosine of the phase angle between voltage and current. In a series RLC circuit, it is equal to the ratio of:

A.Resistance to Impedance (R/Z) B.Reactance to Resistance (X/R) C.Voltage to Current (V/I) D.Inductance to Capacitance (L/C)

Q29

What is the expression for the natural angular frequency of free oscillations in an LC circuit?

A.sqrt(L * C) B.L * C C.1 / sqrt(L * C) D.1 / (L * C)

Q30

A 'wattless current' occurs in an AC circuit when the phase difference between voltage and current is:

A.0 degrees B.45 degrees C.90 degrees D.180 degrees

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About this Electromagnetic Induction And Alternating Current test

This free online practice test covers Electromagnetic Induction And Alternating Current from the 12th Standard Physics (Samacheer Kalvi) syllabus. Choose the number of questions and an optional time limit, then answer and submit — everything is checked in your browser, with the correct answers and a worked explanation shown at the end. For the full solutions to every question in this set, see the solved MCQs page.

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