Physics M.C.Q (1 Marks)

Assertion : The quantity L/R possesses dimensions of time.
Reason : To reduce the rate of increases of current through a solenoid should increase the time constant (L/R).

Assertion : The back emf in a dc motor is maximum when the motor has just been switched on.
Reason : When motor is switched on it has maximum speed.

Assertion : An ac generator is based on the phenomenon of self-induction.
Reason : In single coil, we consider self-induction only.

Assertion : Soft iron is used as a core of transformer.
Reason : Area of hysteresis is loop for soft iron is small.

Assertion : A transformer cannot work on dc supply.
Reason : dc changes neither in magnitude nor in direction.

Assertion : A metal piece and a non-metal (stone) piece are dropped from the same height near earth’s surface. Both will reach the earth’s surface simultaneously.
Reason : There is no effect of earth’s magnetic field on freely falling body.

Assertion : A bar magnet is dropped into a long vertical copper tube. Even taking air resistance as negligible, the magnet attains a constant terminal velocity. If the tube is heated, the terminal velocity gets increased.
Reason : The terminal velocity depends on eddy current produced in bar magnet.

Assertion : An artificial satellite with a metal surface is moving above the earth in a circular orbit. A current will be induced in satellite if the plane of the orbit is inclined to the plane of the equator.
Reason : The current will be induced only when the speed of satellite is more than 8 km/sec.

Assertion : The induced emf in a conducting loop of wire will be non zero when it rotates in a uniform magnetic field.
Reason : The emf is induced due to change in magnetic flux.

Assertion : Lenz’s law violates the principle of conservation of energy.
Reason : Induced e.m.f., opposes always the change in magnetic flux responsible for its production.

Assertio : In the phenomenon of mutual induction, self induction of each of the coils persists.
Reason : Self induction arises when strength of current in same coil changes. In mutual induction, current is changing in both the individual coils.

Assertion : A spark occur between the poles of a switch when the switch is opened.
Reason : Current flowing in the conductor produces magnetic field.

Assertion : An aircraft flies along the meridian, the potential at the ends of its wings will be the same.
Reason : Whenever there is change in the magnetic flux e.m.f. induces.

Assertion : Acceleration of a magnet falling through a long solenoid decreases.
Reason : The induced current produced in a circuit always flow in such direction that it opposes the change or the cause the produced it.

Assertion : When two coils are wound on each other, the mutual induction between the coils is maximum.
Reason : Mutual induction does not depend on the orientation of the coils.

Assertion : Self-inductance is called the inertia of electricity.
Reason : Self-inductance is the phenomenon, according to which an opposing induced e.m.f. is produced in a coil as a result of change in current or magnetic flux linked in the coil.

Assertion : Inductance coil are made of copper.
Reason : Induced current is more in wire having less resistance.

Assertion : The induced e.m.f. and current will be same in two identical loops of copper and aluminium, when rotated with same speed in the same magnetic field.
Reason : Induced e.m.f. is proportional to rate of change of magnetic field while induced current depends on resistance of wire.

Assertion : Magnetic flux can produce induced e.m.f.
Reason : Faraday established induced e.m.f. experimentally.

Assertion : Only a change in magnetic flux will maintain an induced current the coil.
Reason : The presence of large magnetic flux through a coil maintains a current in the coil if the circuit is continuous.

Assertion : Faraday’s laws are consequences of conservation of energy.
Reason : In a purely resistive ac circuit, the current lags behind the e.m.f. in phase.

A magnet is made to oscillate with a particular frequency, passing through a coil as shown in figure. The time variation of the magnitude of e.m.f. generated across the coil during one cycle is

The figure shows three circuits with identical batteries, inductors, and resistors. Rank the circuits according to the current through the battery (i) just after the switch is closed and (ii) a long time later, greatest first

 

A wire cd of length l and mass m is sliding without friction on conducting rails ax and by as shown. The vertical rails are connected to each other with a resistance R between a and b. A uniform magnetic field B is applied perpendicular to the plane abcd such that cd moves with a constant velocity of

Switch S of the circuit shown in figure. is closed at t = 0. If e denotes the induced

emf in L and i, the current flowing through the circuit at time t, which of the following graphs is correct

In an L–R circuit connected to a battery the rate at which energy is stored in the inductor is plotted against time during the growth of the current in the circuit. Which of the following best represents the resulting curve

The current i in an induction coil varies with time t according to the graph shown

in figure. Which of the following graphs shows the induced emf (e) in the coil with time

When a certain circuit consisting of a constant e.m.f. E an inductance L and a resistance R is closed, the current in, it increases with time according to curve 1. After one parameter (E, L or R) is changed, the increase in current follows curve 2 when the circuit is closed second time. Which parameter was changed and in what direction

When a battery is connected across a series combination of self inductance L and resistance R, the variation in the current i with time t is best represented by

A rectangular loop is being pulled at a constant speed v, through a region of certain thickness d, in which a uniform magnetic field B is set up. The graph between position x of the right hand edge of the loop and the induced emf E will be

Figure (i) shows a conducting loop being pulled out of a magnetic field with a speed v. Which of the four plots shown in figure (ii) may represent the power delivered by the pulling agent as a function of the speed v

The graph gives the magnitude B(t) of a uniform magnetic field that exists throughout a conducting loop, perpendicular to the plane of the loop. Rank the five regions of the graph according to the magnitude of the emf induced in the loop, greatest first

Some magnetic flux is changed from a coil of resistance 10 ohm. As a result an induced current is developed in it, which varies with time as shown in figure. The magnitude of change in flux through the coil in webers is

A horizontal loop abcd is moved across the pole pieces of a magnet as shown in fig. with a constant speed v. When the edge ab of the loop enters the pole pieces at time t = 0 sec. Which one of the following graphs represents correctly the induced emf in the coil

An alternating current of frequency 200 rad/sec and peak value 1A as shown in the figure, is applied to the primary of a transformer. If the coefficient of mutual induction between the primary and the secondary is 1.5 H, the voltage induced in the secondary will be

The current through a 4.6 H inductor is shown in the following graph. The induced emf during the time interval t = 5 milli-sec to 6 milli-sec will be

The variation of induced emf (E) with time (t) in a coil if a short bar magnet is moved along its axis with a constant velocity is best represented as

The graph Shows the variation in magnetic flux ∅(t) with time through a coil. Which of the statements given below is not correct

A simple pendulum with bob of mass m and conducting wire of length L swings under gravity through an angle 2θ. The earth’s magnetic field component in the direction perpendicular to swing is B. Maximum potential difference induced across the pendulum is

A conducting ring of radius 1 meter is placed in an uniform magnetic field B of 0.01Telsa oscillating with frequency 100Hz with its plane at right angles to B. What will be the induced electric field

As shown in the figure a metal rod makes contact and complete the circuit. The circuit is perpendicular to the magnetic field with B = 0.15 tesla. If the resistance is 3Ω, force needed to move the rod as indicated with a constant speed of 2m/sec is

A coil of inductance 8.4 mH and resistance 6 W is connected to a 12 V battery. The current in the coil is 1.0 A at approximately the time

A rectangular loop with a sliding connector of length l = 1.0 m is situated in a uniform magnetic field B = 2T perpendicular to the plane of loop. Resistance of connector is r = 2W. Two resistance of 6W and 3W are connected as shown in figure. The external force required to keep the connector moving with a constant velocity v = 2m/s is

Plane figures made of thin wires of resistance R = 50 milli ohm/metre are located in a uniform magnetic field perpendicular into the plane of the figures and which decrease at the rate dB/dt = 0.1 m T/s. Then currents in the inner and outer boundary are. (The inner radius a = 10 cm and outer radius b = 20 cm)

The north and south poles of two identical magnets approach a coil, containing a condenser, with equal speeds from opposite sides. Then

A conducting ring is placed around the core of an electromagnet as shown in fig. When key K is pressed, the ring

The resistance in the following circuit is increased at a particular instant. At this instant the value of resistance is 10W. The current in the circuit will be now

A conducting rod PQ of length L = 1.0 m is moving with a uniform speed v = 2 m/s in a uniform magnetic field B = 4.0T directed into the paper. A capacitor of capacity C = 10 mF is connected as shown in figure. Then

A copper rod of length l is rotated about one end perpendicular to the magnetic field B with constant angular velocity ω. The induced e.m.f. between the two ends is

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

A conducting wire frame is placed in a magnetic field which is directed into the paper. The magnetic field is increasing at a constant rate. The directions of induced current in wires AB and CD are

A current carrying solenoid is approaching a conducting loop as shown in the figure. The direction of induced current as observed by an observer on the other side of the loop will be

In the following figure, the magnet is moved towards the coil with a speed v and induced emf is e. If magnet and coil recede away from one another each moving with speed v, the induced emf in the coil will be

Two identical coaxial circular loops carry current i each circulating in the clockwise direction. If the loops are approaching each other, then

An inductor of 2 henry and a resistance of 10 ohms are connected in series with a battery of 5 volts. The initial rate of change of current is

A small square loop of wire of side l is placed inside a large square loop of wire of side L (L > l). The loop are coplanar and their centre coincide. The mutual inductance of the system is proportional to

Two identical circular loops of metal wire are lying on a table without touching each other. Loop-A carries a current which increases with time. In response, the loop-B

A metallic square loop ABCD is moving in its own plane with velocity v in a uniform magnetic field perpendicular to its plane as shown in the figure. An electric field is induced

A circular loop of radius R carrying current I lies in x-y plane with its centre at origin. The total magnetic flux through x-y plane is

Consider the situation shown in the figure. The wire AB is sliding on the fixed rails with a constant velocity. If the wire AB is replaced by semicircular wire, the magnitude of the induced current will

A thin semicircular conducting ring of radius R is falling with its plane vertical in a horizontal magnetic induction B. At the position MNQ, the speed of the ring is V and the potential difference developed across the ring is

An e.m.f. of 15 volt is applied in a circuit containing 5 henry inductance and 10 ohm resistance. The ratio of the currents at time t = ∞ and at t = 1 second is

Two circular coils can be arranged in any of the three situations shown in the figure. Their mutual inductance will be

A uniform but time-varying magnetic field B(t) exists in a circular region of radius a and is directed into the plane of the paper, as shown. The magnitude of the induced electric field at point P at a distance r from the centre of the circular region

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

In a step up transformer, if ratio of turns of primary to secondary is 1 : 10 and primary voltage is 230 V. If the load current is 2A, then the current in primary is

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

A short-circuited coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the electrical power dissipated would be

In a transformer, the number of turns in primary and secondary are 500 and 2000 respectively. If current in primary is 48 A, the current in the secondary is

The induction coil works on the principle of

The turn ratio of a transformers is given as 2 : 3. If the current through the primary coil is 3 A, thus calculate the current through load resistance

Quantity that remains unchanged in a transformer is

In an inductor of inductance L = 100 mH, a current of I = 10A is flowing. The energy stored in the inductor is

In a step up transformer, 220 V is converted into 200 V. The number of turns in primary coil is 600. What is the number of turns in the secondary coil

A step up transformer has transformation ration 5 : 3. What is voltage in secondary if voltage in primary is 60 V

In a primary coil 5A current is flowing on 220 volts. In the secondary coil 2200V voltage produces. Then ratio of number of turns in secondary coil and primary coil will be

An ideal transformer has 500 and 5000 turn in primary and secondary windings respectively. If the primary voltage is connected to a 6V battery then the secondary voltage is

A transformer has 100 turns in the primary coil and carries 8 A current. If input power is one kilowatt, the number of turns required in the secondary coil to have 500V output will be

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 in primary and secondary coil is

A step-up transformer has transformation ratio of 3 : 2. What is the voltage in secondary if voltage in primary is 30 V

The primary winding of transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an ac supply of 20 V, 50 Hz. The secondary will have an output of

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

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

A transformer is used to

In a transformer the primary has 500 turns and secondary has 50 turns. 100 volts are applied to the primary coil, the voltage developed in the secondary will be

A step up transformer connected to a 220 V AC line is to supply 22 kV for a neon sign in secondary circuit. In primary circuit a fuse wire is connected which is to blow when the current in the secondary circuit exceeds 10 mA. The turn ratio of the transformer is

A power transformer is used to step up an alternating e.m.f. of 220 V to 11 kV to transmit 4.4 kW of power. If the primary coil has 1000 turns, what is the current rating of the secondary ? Assume 100% efficiency for the transformer

In a transformer, number of turns in the primary are 140 and that in the secondary are 280. If current in primary is 4A then that in the secondary is

In a step-up transformer the voltage in the primary is 220 V and the current is 5A. The secondary voltage is found to be 22000V. The current in the secondary (neglect losses) is

Large transformers, when used for some time, become hot and are cooled by circulating oil. The heating of transformer is due to

In a step-up transformer the turn ratio is 1:10. A resistance of 200 ohm connected across the secondary is drawing a current of 0.5 A. What is the primary voltage and current

A transformer has turn ratio 100/1. If secondary coil has 4 amp current then current in primary coil is

Voltage in the secondary coil of a transformer does not depend upon.

The ratio of secondary to primary turns is 9 : 4. If power input is P, what will be the ratio of power output (neglect all losses) to power input

The number of turns in primary and secondary coils of a transformer are 100 and 20 respectively. If an alternating potential of 200 volt is applied to the primary, the induced potential in secondary will be

The transformation ratio in the step-up transformer is

In a lossless transformer an alternating current of 2 amp is flowing in the primary coil. The number of turns in the primary and secondary coils are 100 and 20 respectively. The value of the current in the secondary coil is

In transformer, core is made of soft iron to reduce

A transformer is employed to

The coils of a step down transformer have 500 and 5000 turns. In the primary coil an ac of 4 ampere at 2200 volts is sent. The value of the current and potential difference in the secondary coil will be

The efficiency of transformer is very high because

A 100% efficient transformer has 100 turns in the primary and 25 turns in its secondary coil. If the current in the secondary coil is 4 amp, then the current in the primary coil is

We can reduce eddy currents in the core of transformer

The alternating voltage induced in the secondary coil of a transformer is mainly due to

In a step-up transformer, the turn ratio is 1 : 2. A Leclanche cell (e.m.f. 1.5V) is connected across the primary. The voltage developed in the secondary would be

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

An ideal transformer has 100 turns in the primary and 250 turns in the secondary. The peak value of the ac is 28 V. The r.m.s. secondary voltage is nearest to

A step-down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in primary coil will be

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 the secondary are

The ratio of secondary to the primary turns in a transformer is 3 : 2. If the power output be P, then the input power neglecting all loses must be equal to

In a transformer 220 ac voltage is increased to 2200 volts. If the number of turns in the secondary are 2000, then the number of turns in the primary will be

The core of a transformer is laminated so that

What is increased in step-down transformer

A motor having an armature of resistance 2Ω is designed to operate at 220 V mains. At full speed, it develops a back e.m.f. of 210V. When the motor is running at full speed, the current in the armature is

An electric motor operates on a 50 volt supply and a current of 12A. If the efficiency of the motor is 30%, what is the resistance of the winding of the motor

A device which converts electrical energy into mechanical energy is

An electric motor operating on a 60 V dc supply draws a current of 10 A. If the efficiency of the motor is 50%, the resistance of its winding is

Work of electric motor is

In a dc motor, induced e.m.f. will be maximum

In an induction coil, the secondary e.m.f. is

Eddy currents are produced when

The armature of dc motor has 20Ω 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

Armature current in dc motor will be maximum when

Dynamo core is laminated because

The coil of dynamo is rotating in a magnetic field. The developed induced e.m.f. changes and the number of magnetic lines of force also changes. Which of the following condition is correct

Which of the following statement is incorrect

The output of a dynamo using a splitting commutator is

When the speed of a dc motor increases the armature current

Choke coil works on the principle of

The working of dynamo is based on principle of

Dynamo is a device for converting

If rotational velocity of a dynamo armature is doubled, then induced e.m.f. will become

If the current 30 A flowing in the primary coil is made zero in 0.1 sec. The emf induced in the secondary coil is 1.5 volt. The mutual inductance between the coil is

The device that does not work on the principle of mutual induction is

The pointer of a dead-beat galvanometer gives a steady deflection because

The core of a transformer is laminated to reduce energy losses due to

Which of the following is not an application of eddy currents

Use of eddy currents is done in the following except

Plane of eddy currents makes an angle with the plane of magnetic lines of force equal to

Which of the following is constructed on the principle of electromagnetic induction

A transformer is based on the principle of

A coil having an inductance of 0.5 H carries a current which is uniformly varying from zero to 10 ampere in 2 second. The e.m.f. (in volts) generated in the coil is

The square root of the product of inductance and capacitance has the dimension of

An oscillator circuit consists of an inductance of 0.5mH and a capacitor of 20 μF. The resonant frequency of the circuit is nearly

A LC circuit is in the state of resonance. If C = 0.1μF and L = 0.25 henry. Neglecting ohmic resistance of circuit what is the frequency of oscillations

The time constant of an LR circuit represents the time in which the current in the circuit

A coil of inductance 40 henry is connected in 0series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is

A capacitor is fully charged with a battery. Then the battery is removed and coil is connected with the capacitor in parallel, current varies as

In the figure magnetic energy stored in the coil is

An inductance L and a resistance R are first connected to a battery. After some time the battery is disconnected but L and R remain connected in a closed circuit. Then the current reduces to 37% of its initial value in

In L-R circuit, for the case of increasing current, the magnitude of current can be calculated by using the formula

Eddy currents are used in

The current through choke coil increases form zero to 6A in 0.3 seconds and an induced e.m.f. of 30 V is produced. The inductance of the coil of choke is

The current in a coil decreases from 1 A to 0.2 A. In 10sec. Calculate the coefficient of self inductance. If induced emf is 0.4 volt.

Two circular coils have their centres at the same point. The mutual inductance between them will be maximum when their axes

Why the current does not rise immediately in a circuit containing inductance

A solenoid of length l metre has self-inductance L henry. If number of turns are doubled, its self inductance

Energy stored in a coil of self inductance 40mH carrying a steady current of 2 A is

A coil of resistance 10 W and an inductance 5H is connected to a 100 volt battery. Then energy stored in the coil is

An average induced e.m.f. of 1V appears in a coil when the current in it is changed from 10A in one direction to 10 A in opposite direction in 0.5 sec. Self-inductance of the coil is

A coil resistance 20W and inductance 5H is connected with a 100V battery. Energy stored in the coil will be

When the current change from + 2A to – 2A in 0.05 second, an e.m.f. of 8 V is induced in a coil. The coefficient of self-induction of the coil is

Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon

An L-R circuit has a cell of e.m.f. E, which is switched on at time t = 0. The current in the circuit after a long time will be

Two circuits have mutual inductance of 0.1 H. What average e.m.f. is induced in one circuit when the current in the other circuit changes from 0 to 20 A in 0.02 s

The self-induced e.m.f. in a 0.1 H coil when the current in it is changing at the rate of 200 ampere/second is

The current in a coil of inductance 5 H decreases at the rate of 2 A/s. The induced e.m.f. is

Which of the following is not the unit of self inductance

Find out the e.m.f. produced when the current changes from 0 to 1 A in 10 second, given L = 10 mH

Pure inductance of 3.0 H is connected as shown below. The equivalent inductance of the circuit is

The current in a coil changes from 4 ampere to zero in 0.1 s. If the average e.m.f. induced is 100 volt, what is the self inductance of the coil

The self inductance of a straight conductor is

A 100 mH coil carries a current of 1 ampere. Energy stored in its magnetic field is

A coil has an inductance of 2.5 H and a resistance of 0.5 r. If the coil is suddenly connected across a 6.0 volt battery, then the time required for the current to rise 0.63 of its final value is

An e.m.f. of 12 volt is produced in a coil when the current in it changes at the rate of 45 amp/minute. The inductance of the coil is

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 two inductances is

When the current through a solenoid increases at a constant rate, the induced current

The inductance of a closed-packed coil of 400 turns is 8 mH. A current of 5 mA is passed through it. The magnetic flux through each turn of the coil is

A circular coil of radius 5 cm has 500 turns of a wire. The approximate value of the coefficient of self induction of the coil will be

The inductance of a coil is 60μH. A current in this coil increases from 1.0 A to 1.5 A in 0.1 second. The magnitude of the induced e.m.f. is

The number of turns of primary and secondary coils of a transformer are 5 and 10 respectively and the mutual inductance of the transformer is 25 henry. Now the number of turns in the primary and secondary of the transformer are made 10 and 5 respectively. The mutual inductance of the transformer in henry will be

An ideal coil of 10 henry is joined in series with a resistance of 5 ohm and a battery of 5 volt. 2 second after joining, the current flowing in ampere in the circuit will be

If a current of 10 A flows in one second through a coil, and the induced e.m.f. is 10 V, then the self-inductance of the coil is

A varying current at the rate of 3 A/s in a coil generates an e.m.f. of 8 mV in a nearby coil. The mutual inductance of the two coils is

The current flowing in a coil of self inductance 0.4 mH is increased by 250 mA in 0.1 sec. The e.m.f. induced will be

Which of the following is wrong statement

A varying current in a coil changes from 10 amp to zero in 0.5 sec. If average EMF is induced in the coil is 220 volts, the self inductance of coil is

If the current is halved in a coil, then the energy stored is how much times the previous value 

The average e.m.f. induced in a coil in which a current changes from 0 to 2 A in 0.05 s is 8 V. The self inductance of the coil is

The energy stored in a 50 mH inductor carrying a current of 4 A will be

The mutual inductance between a primary and secondary circuits is 0.5 H. The resistances of the primary and the secondary circuits are 20 ohms and 5 ohms respectively. To generate a current of 0.4 A in the secondary, current in the primary must be changed at the rate of

The self inductance of a coil is L. Keeping the length and area same, the number of turns in the coil is increased to four times. The self inductance of the coil will now be

A coil of self inductance 50 henry is joined to the terminals of a battery of e.m.f. 2 volts through a resistance of 10 ohm and a steady current is flowing through the circuit. If the battery is now disconnected, the time in which the current will decay to 1/e of its steady value is

In a coil of self inductance 0.5 henry, the current varies at a constant rate from zero to 10 amperes in 2 seconds. The e.m.f. generated in the coil is

An e.m.f. of 100 millivolts is induced in a coil when the current in another nearby coil becomes 10 ampere from zero in 0.1 second. The coefficient of mutual induction between the two coils will be

5 cm long solenoid having 10 ohm resistance and 5 mH inductance is joined to a 10 volt battery. At steady state the current through the solenoid in ampere will be

The momentum in mechanics is expressed as m × v. The analogous expression in electricity is

The unit of inductance is

The self inductance of a coil is 5 henry, a current of 1 amp change to 2 amp within 5 second through the coil. The value of induced e.m.f. will be

Mutual inductance of two coils can be increased by