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Syllabus

when 100v dc is applied across a solenoid a current of 1A flows in it. when 100v ac is applied across the same coil the current drops to 0.5A the frequency of the ac is 50hz.the impendence and inductance of the solenoid are

Show that weber = volt x second

a 12ohm resistor and a 0.21H inductor are connected in series to an ac source operating at 20V, 50cycle/second . the phase angle between current and source voltage is

1) 30degree

2) 40

3) 80

4) 90

if 10 m long metallic bar moves in a direction at right angles to the magnetic field with a speed of 5 m/s ,25v emfis induced in it. finf the value of magnetic field intensity?

^{2}is connectes in series with galvanometer of resistance of 45 ohm,,,,The coil is placed between poles of an electromagnet....When the coil is withdrawn from the pole pieces in 1ms,,,,the charge flowing in galvanometer is 2mc,,,,,The magnetic field of electromagnet is??the magnetic flux(x) through a stationary loop with resistance R varies during interval of time T as x= at(T-t). The heat generated during this time neglecting the inductance of loop will be

1) a

^{2}T^{3}/3R2) a

^{2}T^{2}/3R3) a

^{2}T/3R4) a

^{3}T^{2}/3RA small coil of radius r is placed at the centre of a large coil of radius R, where Rr . The two coils are coplanar . Then what is the mutual induction b/w the coils.

A long solenoid of radius 2 cm has 100 turns/cm carries a current of 5A.A coil of radius 1cm having 100 turns and a total resistance of 20 ohm is placed inside the solenoidf coaxially . The coil is connected to a galvanometer.If the current in the galvanometer is reversed in direction ,find the charge flown through the galvanometer .

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

ans: 5 sec

the length of thin wire required to manufacture a solenoid of inductance L and length l,(if cross section diameter is considered less than its lenght)is

1) {(pie)Ll/2(nu not)}1/2

2) {4(pie)Ll/(nu not)}1/2

3) {2(pie)Ll/(nu not)}1/2

4) {(pie)Li/(nu not)}

^{1/2}Why the steel used is of high silicon content in a transformer?

a wire of fixed length is wound on a solenoid of length l and radius r . its self inductance is found to be L . now if same wire is wound on a solenoid of length l/2 and radius r/2 , then self inductance will be

ans: 2L

why not L/2

what is the magnitude and direction of the magnetic induction at the centre of two concentric coils of same radius inclined at an angle 90 when same current is passing through the coils

the phase difference between current and voltage in an AC circuit is pie/4 radian . if the frequency of AC is 50Hz, then the phase difference is equivalent to the time difference of

1) 0.75s

2) 10.5ms

3) 2.5ms

3) 0.25ms

In chapter "Electromagnetic Induction" of Physics, its first topic "Experiment of Faraday and Henry Magnitic Flux Faraday/'s Law of Induction", it's aExaple no. 7. I have not understood it at all. How this problem is solved? What formulas are used? Why they are not explained above?

Example :

A long solenoid of diameter 0.1 m hasturns per meter. At the centre of the solenoid, a 100 turn coil of radius 0.01 m is placed with its axis coinciding with the solenoid axis. The current in the solenoid is decreased at a constant rate from +2 A to 2 A in 0.05 s. Find the emf induced in the coil. Also find the total charge that flows through the coil during this time if the resistance of the coil is.

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 turn were to be quadrupled and the wire radius halved, electric power dissipiated would be

1) halved

2) same

3) doubled

4) quadrupled

a conductor of 3m length is moving perpendicular to its length as well as magnetic field of 10

^{-3}T with a speed of 10^{2}m/s , then force required to move it with this constant speed is1) 0.3 N

2) 0.9

3) 0

4) 3*10

^{-3}What does polarity mean in lenz law and how to determine the direction of induced emf?

a vertical rod of lenght l is moved with constant velocity v towards east. the vertical components of earth magnetic field is B and angle of dip is 'x'. the induced e.m.f. in rod is

1) Blvsinx

2) Blvtanx

3) Blv cotx

4) Blv cosx

Consider a region of cylindrical magnetic field ,changing with time at a rate x . A triangular conducting loop PQR is placed in the field such that the mid point of side PQ coincide with the axis of the magnetic field region .PQ=2l ,PR=2l.emf induced in the sides PQ,QR and PR of the loop are

a sheet of relative permeability 100is placed inside a solenoid , so as to fill the space . what will be the energy stored inside the solenoid.?

radius of a circular loop placed in a perpendicular uniform magnetic field is increasing at a constant rate of r1 m/s. if at any instant radius of the loop is r, then emf induced in the loop at that instan twill be

1) -2Brr1

2) -2B(pie) r

3)-B(pie)r1r

4) -2B(pie)r1r

In the figure, the arm PQ is moved from x = 0 to x = 2b with constant speed V. Consider the magnetic field as shown.

Write:-

how to find the direction of the induced current by using the Lenz rule?

(a) north-south direction

(b) east west direction

when the wire is allowed to fall freely, will there be induced emf set up in the wire? Justify your answer giving reasons for both the above mentioned cases

2nd Reminder: Please answer:A potentiometer circuit consists of a resistance r in the primary and secondary circuit both . the potentiometer wire is 600 cm long and its resistance is 15r . emf of driving cell is E and the emf of the experimental cell is E/2. 1. at what distance from the leftend should the jockey touch the wire to get zero deflection int the galvanometer . 2.if the jockey touches the wire at a distance 560 cm from the left end , what will be the current in the galvanometer ?

two coils have self inductance L1 = 4mH and L2= 1mH resp. the currents in the two coils are increased at the same rate. at a certain instant of time both coils are given the same power. If i1 and i2 are the currents in the two coils, at that instant of timw respectively, then the value of i1/i2 is

1) 1/8

2) 1/4

3) 1/2

4)1

Define 1 henry inductance.

for a coil having L= 2mH , current flowing through it is i=t

^{2}e^{-t}then the time at which emf become zero1) 2s

3) 1s

3) 4s

4) 3s

A 12V battery connected to a 6 ohms,10 H coil through a switch drives a constant current in the circuit. The switch is suddenly opened. Assuming that it took 1ms to open the switch ,calculate the average emf induced across the coil.

A coil and a bulb are connected in series with a do source. A soft iron Core is then inserted in the coil, then

A) intensity of the bulb remains the same

B) intensity of the bulb decreases

C) intensity of the bulb increases

D) the bulb ceases to glow

A closed coil having 100 turns is rotated in a uniform magnetic field b=4*10

^{4}T about a diameter which is perpendicular to the field . The angular velocity of rotation is 300 rev/min .the area of the coil is 25 cm^{2}and its resistance is 4 ohm . find- 1. average emf developed in half a turn from a position where the coil is perpendicular to the magnetic field 2. averageemf in full turn 3.net charge displaced in part 1.an ac current is given by

=(3sinwt+4coswt) the rms speed will be

A metal rod of resistance R is fixed along a diameter of a conducting ring of radius r . There is a magnetic field of magnitude B perpendicular to the plane of the loop . The ring spins with an angular velocity w about its axis . The centre of the ring is joined to its rim by an external wire W.The ring and W have no resistance . The current in W is

^{2}w/2R^{2}w/R^{2}w/RWhy in Faradays all experiments coils are made of conducting material s cant they be made of insulating material.

A potentiometer circuit consists of a resistance r in the primary and secondary circuit both . the potentiometer wire is 600 cm long and its resistance is 15r . emf of driving cell is E and the emf of the experimental cell is E/2. 1. at what distance from the leftend should the jockey touch the wire to get zero deflection int the galvanometer . 2.if the jockey touches the wire at a distance 560 cm from the left end , what will be the current in the galvanometer ?

A circuit has a self inductance of 1 henry and carries a current of 2A . To prevent sparkling when the circuit is switched off , a capacitor which can withstand 400V is used . The least capacitance of the capacitor connected across the switch must be equal to

The ring of radius r moves with the speed v in a horizontal surface in a uniform horizontal magnetic field B normal to the plane of ring . Then what is the induced emf produced in the ring.

Expalin how the strength of Eddy current can be reduced.

There exists a uniform magnetic field B=Botk in a region. A circular conducting loop of radius r and resistance R is placed with its plane in x-y plane. Determine the current through the loop and tension at time t developed in the loop as a result of induced current.

Q) AB and CD are fixed conducting smooth rails placed in a vertical plane and joined by a constant source at its upper end. PQ is a conducting rod which is free to slide on the rails. A horizontal uniform magnetic field exists in space. If the rod PQ in released from rest then,

Correct answer: The rod PQ will move downward with constant acceleration and the rod PQ will move upward with contant acceleration.

A capacitor is used in the primary circuit of an induction coil. explain in detail.pls with required fig...

A wire as a parabola y=ax

^{2}is located in a uniform magnetic field of inductance B, the vector B being perpendicular to the plane xy. At the moment t=0 a connector start translation wise from the parabola apex with a constant acceleration 'w' to find the emf of elecromagnetic induction in the loop this formed as a function of y ....................^{2}gR^{2}/(2B^{4}l^{4})If the rod were translating as well as rotating, what will be its emf? Assume that the centre of mass has a velocity v and the rod is rotating with an angular velocity omega about its centre of mass.

A flat coil , of n turns , area A and resistance R is placed in a uniform magnetic field of magnitude B. The plane of the coil is initially perpendicular to B . If the coil is rotated by an angle

~~O~~about the axis XY , charge of amout Q flows through ita. if

~~O~~= 90^{o}, Q = BAn/Rb. if

~~O~~= 180^{o}, Q = BAn/Rc. if

~~O~~= 180^{o}, Q = 0d. if

~~O~~= 360^{o}, Q = 0Which options are correct

A small magnet M is allowed to fall through a fixed horizontal conducting ring R. Let g be the acceleration due to gravity. The acceleration if M will be

a. less than g when it is above R and moving towards R

b. greater than g when it is above R and moving towards R

c. less than g when it is below R and moving away R

d. greater than g when it is below R and moving away R

^{.}.Calculate the emf induced between the axle and the rim of the wheel .PLEASE ANSWER SOON...

A FAN BLADE OF LENGTH 2a ROTATES WITH FREQUENCY f PERCYCLE PERPENDICULAR TO MAGNETIC FIELD B.THEN POTENTIAL DIFFERENCE BETWEEN CENTRE AND END OF BLADE IS

A--piBa^2f

B--4pia^2Bf

Why an induced current has no direction of its own?

AB and CD are smooth parallel rails , seperated by a distance l , and inclined to the horiqontal at an angle

~~O~~. A uniform magnetic field is normal to the plane of the rails . EF is a conductor of mass m , carrying a current i .For EF to be in equilibriuma. Bil = mg tan

~~O~~b. Bil = mg sin

~~O~~c. Bil = mg cos

~~O~~d. equilibrium cannot be reached

A closed loop is held stationary in the magnetic field between the north and south poles of two bar magnets held fixed .Can we hope to generate current in the loop by using very strong magnets?

The answer is NO. please explain me why?

A long solenoid of radius 2 cm has 100 turns/cm and carries a current of 5 A. A coil of radius 1 cm having 100 turns and a total resistance of 20 Ω is placed inside the solenoid coaxially. The coil is connected to a galvanometer. If the curret in the solenoid is reversed in direction, find the charge flown through through the galvanometer.

A circular disk of radius r is rotating in the xy plane and there is a uniform magnetic field B in the z direction. How to find the emf between the center and the rim of the disk? The ring is conducting.

what r eddy currents.tell me in detail.i need it

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

ans:80J

ans should be 0.08J or 80 J

define eddy currents and explain there formation?? why does the eddy currents stop the motion of the coil??

state the underlying principle of a transformer.

_{1}(t) start flowing through the coil. if I_{2}(t)is the current induced in the ring, and B(t) is magnetic field at the axis of coil due to I_{1}(t), then as a function of time (t.0) the product I_{2}(t) B(t)-----when a wire loop is rotated in a magnetic field,the direction of induced e.m.f. changes once in each a) 1/4 revolution b) 1/2 revolution c) 1 revolution d) 2 revolution

an electron beam passes through a

_{}_{REGION OF CROSSED ELECTRIC AND MAGNETIC FIELDS OF INTENSITIES}E and B RESPECTIVELY. FOR WHAT VALUE OF THE ELECTRON SPPED WILL THE ELECTRON BEAM REMAIN UNDEFLECTED?what is the power dissipation in an AC CIRCUIT in which the voltage and the current are given byV =200sin(wt+pi/2) and I =5sinwt

A picnic was arranged by school for the students of XII class. After some time it was raining heavily accompanied by thundering lightening. The Student got afraid. Some students went inside the room. Two students asked for the key of the car and sat inside the car folding their legs on the seat. The other students called them to come out but they refused. They knew that charge inside the conducting shell is zero as told by the teacher and told others not to stand near the electric pole when it is lightning.

What value was displayed by these students? Write any two safety measures to protect from lightning.