JEE Questions for Physics Electromagnetic Induction Quiz 12 - MCQExams.com

The inductance of a solenoid 0.5 m long of cross-sectional area 20 cm2 and with 500 turns is
  • 12.5 mH
  • 1.25 mH
  • 15.0 mH
  • 0.12 mH
The equivalent inductance of two inductances is 2.4 henry when connected in parallel and 10 henry when connected in series. The difference between the twoinductances is
  • 2 henry
  • 3 henry
  • 4 henry
  • 5 henry
An average induced e.m.f. of 1 V appears in a coil when the current in it is changed from 10 A in one direction to 10 A in opposite direction in 0.5 sec. Self-inductance of the coils is
  • 25 mH
  • 50 mH
  • 75 mH
  • 100 mH
A coil of resistance 10 Ω and an inductance 5 H is connected to a 100 volt battery. Then energy stored in the coil is
  • 125 erg
  • 125 J
  • 250 erg
  • 250 J
If a change in current of 0.01 A in one coil produces a change in magnetic flux of 1.2 × 10–2 Wb in the other coil, then the mutual inductance of the two coils inhenry is
  • 0
  • 0.5
  • 1.2
  • 3
Two coils of self-inductances 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutualinductance between these coils is
  • 4 mH
  • 16 mH
  • 10 mH
  • 6 mH
Two coils A and B having turns 300 and 600 respectively are placed near each other, on passing a current of 3.0 ampere in A, the flux linked with A is 1.2 × 10–4 weber and with B it is 9.0 × 10–5 weber. Themutual inductance of the system is
  • 2 × 10–5 henry
  • 3 × 10–5 henry
  • 4 × 10–5 henry
  • 6 × 10–5 henry
An inductor L, a resistance R and two identical bulbs, B1 and B2 are connected to a battery through a switch S as shown in the figure. The resistance R is the same as that of the coil that makes L. Which of the following statements gives the correct description of the happenings when the switch S is closed
Physics-Electromagnetic Induction-69381.png
  • The bulb B2 lights up earlier than B1 and finally both the bulbs shine equally bright
  • B1 light up earlier and finally both the bulbs acquire equal brightness
  • B2 lights up earlier and finally B2 shines brighter than B2
  • B1 and B2 light up together with equal brightness all the time
An air core solenoid has 1000 turns and is one metre long. Its cross-sectional area is 10 cm2. Its self-inductance is
  • 0.1256 mH
  • 12.56 mH
  • 1.256 mH
  • 125.6 mH
An inductance L and a resistance R are first connected to a battery. After sometime the battery is disconnectedbut L and R remain connected in a closed circuit. Thenthe current reduces to 37% of its initial value in
  • RL sec
  • R/L sec
  • L/R sec
  • 1/LR sec
Why the current does not rise immediately in a circuit containing inductance
  • Because of induced e.m.f.
  • Because of high voltage drop
  • Because of low power consumption
  • Because of Joule heating
Two circular coils have their centres at the same point. The mutual inductance between them will be maximum when their axes.
  • Are parallel to each other
  • Are at 60° to each other
  • Are at 45° to each other
  • Are perpendicular to each other
The current through choke coil increases from zero to6 A in 0.3 seconds and an induced e.m.f. of 30 V isproduced. The inductance of the coil of choke is
  • 5 H
  • 2.5 H
  • 1.5 H
  • 2 H
The resistance and inductance of series circuit are 5 Ω and 20 H respectively. At the instant of closing the switch, the current is increasing at the rate 4 A/s. Thesupply voltage is
  • 20 V
  • 80 V
  • 120 V
  • 100 V
The adjoining figure shows two bulbs B1 and B2, resistor R and an inductor L. When the switch S is turned off
Physics-Electromagnetic Induction-69386.png
  • Both B1 and B2 die out promptly
  • Both B1 and B2 die out with some delay
  • B1 dies out promptly but B2 with some delay
  • B2 dies out promptly but B1 with some delay
A solenoid is placed inside another solenoid, the length of both being equal carrying same magnitude of current. The parameters like radius and number of turns are in the ratio 1 : 2 for the two solenoids. The mutual inductance on each other would be
  • M12 = M21
  • M12 = 2M21
  • 2M12 = M21
  • M12 = 4M21
Two solenoids of equal number of turns have their lengths and the radii in the same ratio 1 : 2. The ratio oftheir self-inductances will be
  • 1 : 2
  • 2 : 1
  • 1 : 1
  • 1 : 4
  • 1 : 3
Which of the following is constructed on the principleof electromagnetic induction
  • Galvanometer
  • Electric motor
  • Generator
  • Voltmeter
A transformer is based on the principle of
  • Mutual inductance
  • Self-inductance
  • Ampere's law
  • Lenz's law
Which of the following is not an application of eddycurrents
  • Induction furnace
  • Galvanometer damping
  • Speedometer of automobiles
  • X-ray crystallography
Core of transformer is made up of
  • Soft iron
  • Steel
  • Iron
  • Alnico
The pointer of a dead-beat galvanometer gives a steady deflection because
  • Eddy currents are produced in the conducting frame over which the coil is wound
  • Its magnet is very strong
  • Its pointer is very light
  • Its frame is made of abonite
Eddy currents are produced when
  • A metal is kept in varying magnetic field
  • A metal is kept in the steady magnetic field
  • A circular coil is placed in magnetic field
  • Through a circular coil, current is passed
If rotational velocity of a dynamo armature is doubled, then induced e.m.f. will become
  • Half
  • Two times
  • Four times
  • Unchanged
When the speed of a dc motor increases the armature current
  • Increases
  • Decreases
  • Does not change
  • Increases and decreases continuously
A six pole generator with fixed field excitation develops an e.m.f. of 100 V, when operating at 1500 rpm. At what speed must it rotate to develop 120 V?
  • 1200 rpm
  • 1800 rpm
  • 1500 rpm
  • 400 rpm
The armature of dc motor has 20 Ω resistance. It draws current of 1.5 ampere when run by 220 volts dc supply. The value of back e.m.f. induced in it will be
  • 150 V
  • 170 V
  • 180 V
  • 190 V
A transformer with efficiency 80% works at 4 kW and 100 V. If the secondary voltage is 200 V, then the primary and secondary currents are respectively.
  • 40 A, 16 A
  • 16 A, 40 A
  • 20 A, 40 A
  • 40 A, 20 A
Fan is based on
  • Electric motor
  • Electric dynamo
  • Both of (a) and (b)
  • None of these
What is increased in step-down transformer
  • Voltage
  • Current
  • Power
  • Current density
To core of a transformer is laminated so that
  • Ratio of voltage in the primary and secondary may be increased
  • usting of the core may be stopped
  • Energy losses due to eddy currents may be reduced
  • Change in flux is increased
In transformer, core is made of soft iron to reduce.
  • Hysteresis losses
  • Eddy current losses
  • Force opposing electric current
  • None of the above
A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 amp, the efficiency of the transformer is approximately
  • 30%
  • 50%
  • 90%
  • 10%
The primary winding of a transformer has 100 turns and its secondary winding has 200 turns. The primary is connected to an ac supply of 120 V and the current flowing in it is 10 A. The voltage and the current in thesecondary are
  • 240 V, 5 A
  • 240 V, 10 A
  • 60 V, 20 A
  • 120 V, 20 A
A transformer is employed to reduce 220 V to 11 V. The primary draws a current of 5 A and the secondary 90 A. The efficiency of the transformer is
  • 20%
  • 40%
  • 70%
  • 90%
In a step-up transformer, the turn ratio is 1 : 2. A Leclanche cell (e.m.f. 1.5 V) is connected across the primary. The voltage developed in the secondary wouldbe
  • 3.0 V
  • 0.75 V
  • 1.5 V
  • Zero
The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux ϕ linked with the primary coil is given by ϕ = ϕ0 + 4t, where ϕ is in webers, t is time in seconds and ϕ0, is a constant, the output voltage across the secondary coil is
  • 90 volts
  • 120 volts
  • 220 volts
  • 30 volts
A transformer connected to 220 volt line shows an output of 2 A at 11000 volt. The efficiency is 100%. The current drawn from the line is
  • 100 A
  • 200 A
  • 22 A
  • 11 A
A step-up transformer operates on a 230 V line and supplies a load of 2 ampere. The ratio of the primary and secondary windings is 1 : 25. The current in the primary is
  • 15 A
  • 50 A
  • 25 A
  • 12.5 A
The number of turns in the primary coil of a transformer is 200 and the number of turns in the secondary coil is 10. If 240 volt AC is applied to the primary, the output from the secondary will be
  • 48 V
  • 24 V
  • 12 V
  • 6 V
A step-up transformer has transformation ratio of 3 : 2. What is the voltage in secondary, if voltage in primary is 30 V
  • 45 V
  • 15 V
  • 90 V
  • 300 V
In a transformer, the number of turns in primary coil and secondary coil are 5 and 4 respectively. If 240 V is applied on the primary coil, then the ratio of current inprimary and secondary coil is
  • 4 : 5
  • 5 : 4
  • 5 : 9
  • 9 : 5
When power is drawn from the secondary coil of the transformer, the dynamic resistance
  • Increases
  • Decreases
  • Remains unchanged
  • Changes erratically
In a step-up transformer the voltage in the primary is 220 V and the current is 5 A. The secondary voltage is found to be 22000 V. The current in the secondary (neglect losses) is
  • 5 A
  • 50 A
  • 500 A
  • 0.05 A
In a transformer, number of turns in the primary are 140 and that in the secondary are 280. If current in primary is 4 A, then that in the secondary is
  • 4 A
  • 2 A
  • 6 A
  • 10 A
If a coil made of conducting wires is rotated between poles pieces of the permanent magnet. The motion will generate a current and this device is called
  • An electric motor
  • An electric generator
  • An electromagnet
  • All of these
In a region of uniform magnetic induction B = 10–2 tesla, a circular coil of radius 30 cm and resistance π2 ohm is rotated about an axis which is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating current induced in the coil is
  • 4 π2 mA
  • 30 mA
  • 6 mA
  • 200 mA
A 220 volt input is supplied to a transformer. The output circuit draws a current of 2.0 ampere at 440 volts. If the efficiency of the transformer is 80%, the current drawn by the primary windings of the transformer is
  • 5.0 ampere
  • 3.6 ampere
  • 2.8 ampere
  • 2.5 ampere
In an ac generator, when the plane of the armature is perpendicular to the magnetic field
  • Both magnetic flux and e.m.f. are maximum
  • Both magnetic flux and e.m.f. are zero
  • Both magnetic flux and e.m.f. are half of their respective maximum values
  • Magnetic flux is zero and e.m.f. is maximum
  • Magnetic flux is maximum and e.m.f. is zero
An electron moves along the line AB, which lies in the same plane as a circular loop of conducting wires as shown in the diagram. What will be the direction of current induced if any, in the loop?
Physics-Electromagnetic Induction-69412.png
  • No current will be induced
  • The current will be clockwise
  • The current will be anticlockwise
  • The current will change direction as the electron passes by
0:0:1


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