Question

The working of magnetic braking of trains is based on
A. Steady current
B. Eddy current
C. Alternating current
D. Pulsating current

Answer 1

Hint : Define how a magnetic braking works. Obtain the definition and working of the currents given in the question. The induced current in a conductor due to change in magnetic flux through it opposes the change which induces the current. Use this concept to define magnetic braking.

Complete step by step solution :
In ordinary braking systems we use the concept of friction. In magnetic braking we use the force of magnets.
If we move a conductor through a magnetic field or if we vary the magnetic field through a conductor, a current is produced in it. The induced current induces a magnetic field which opposes the changing magnetic field.
According to Lenz law, the magnetic field created by induced current opposes the initial changing magnetic field which produced it. The direction of this current flow due to the initial changing magnetic field is always given by Fleming's right hand rule.
According to Lenz law, if a magnet is to be moved towards a current carrying coil or vice-versa then the magnetic field produces work in such a way that it always opposes the motion of the current carrying coil.
The above concept is used in magnetic braking. When we move a conductor through a magnetic field a current is induced in the conductor which is called the eddy current. Since this eddy current always opposes the change which produces it, we can use this current in braking.
So, we can say that the working of the magnetic braking is based on eddy current.
The correct option is (B).

Note : The induced magnetic field in the coil due to the electromagnetic induction will always oppose the change in magnetic field or always oppose the motion of the magnet
We can find the direction of induced current by applying the right-hand thumb rule.