EMI 1

Question 1

what do you mean by electromagnetic induction

Answer 1

It is the phenomenon of generating emf or current by changing the magentic flux. This emf developed is called induced emf.

If the conductor is in the form of a closed circuit,then the current set up in the circuit is called induced current.

Question 2

Faraday’s expt 1

Answer 2

• If a coil is placed and a strong bar magnet is brought close it, the galvanometer connected to the coil shows momentary deflection.

-Similarly if the bar magnet is moved away form the coil, galvanometer shows deflection but in the opposite direction.

• It shows that it is the relative
  motion between the magnet and the coil that is
  responsible for generation (induction) of electric
  current in the coil.

Question 3

Faraday’s Expt 2

Answer 3

• If 2 coils are placed together( only one of the coil has current thorugh it), if one of the coils moves towards or away from the other, a current is induced in the other coil.
• If mvmnt is stopped then there is no induced current.
• It is the relative motion between the 2 coils that is responsible for the generation of the current.

Question 4

Farday’s expt 3

Answer 4

• consider 2 coils placed closely together. such that one coil has a current flowing through it. other is conneced to a tapping key.
• it iis due to change in current in of the coil that is reponsible for the induction of the current in the other coil.
• shows relative motion is not required for induction of current.

Question 5

what is magnetic flux?

Answer 5

it is defined as the total no of magnetic field lines passing normally through a given area.

ɸ=B.A

it is a scalar quantity.
Unit: Wb or T/m2

Question 6

State the 2 postulates of Faraday’s law.

Answer 6

i) Whenever the magnetic fluc linked with a closed circuit changes, an emf is induced within it which lasts only as long as the chnage in flux is taking place.

ii) The magnitude of the induced emf is equal to the rate of change of the magnetic flux linked with the closed circuit

ε=dΦ/dt

for N coils, e= ndphi/dt

Question 7

how can the emf induced in a coil be changed?

Answer 7

i) By changing the magnitude of the magnetic field.

ii) by changing the area.

iii) by changing the angle between direction of magnetic field and normal to the surface area by changing the orientation of the area of surface and magnetic field.

Question 8

what is lenz law

Answer 8

The polarity of induced emf is such that it tends to produce a current
which opposes the change in magnetic flux that produced it.

Question 9

explain lenz law with an example

Answer 9

WHen the north pole of a magnet is brought near a coil, the induced current in the coil flows in the anticlockwise direction.

The face of the coil toward the aproaching magnet developed a north polarity and hence oppososes the motion of the north pole of the magnet towards the cell.

The motion of the magnet increases the flux though the coil and induced currrent generated a field hence flux in the opposite direction and reduces the flux.

When the north pole moves away from the coil, the induced current changes to clockwise direction. The face of the coil towards the laving magnet is south polarity and hence attracts the magnet.

The motion of the magnet reduces the flux through the coil. The induced current generates a flux in the same direction and hence increases flux.

Question 10

Prove that lenz law obeys law of conservation of energy.

Answer 10

• When the northpole of the magnet is brought near the coil, the upper face of the coil developed the north polarity and hence work needs to be done agains tthe force of the repulsion to the bring the magnet closer to the coil.

it is this mechanical work done in moving the magnet wrt the coil that changes into electrical energy producing the induced current

When the magnet is not moved, work done is 0 and induced current is 0

Question 11

How is direction of induced current determined

Answer 11

Thumb: motion of conductor
fore finger: mag field

middle finger: induced current

flemings right hand rule is used to determine the direction of induced current