# Electromagnetic Induction - Online Test

Q1. electromagnetic induction i.e currents can be induced in coils (Select the best)
Explaination / Solution:

for electromagnetic induction magnet and coil both may move but relative motion between must be present

Q2. When a bar magnet is pushed towards the coil connected in series with a galvanometer, the pointer in the galvanometer G
Explaination / Solution:

When bar is in motion then flux will changed hence current will be induced.

Q3.

When current carrying coil  is moved towards the coil  connected in series with a galvanometer, the pointer in the galvanometer G

Explaination / Solution:

current induced due to flux changed when C2 is in motion .

Q4. Coils  and  are stationary.  connected in series with a galvanometer while  is connected to a battery through a tapping key. If the tapping key is pressed and released the galvaometer
Explaination / Solution:

flux will be changed when current in C2 is changing. Hence current will be induced in coil C1.

Q5. Magnetic flux (ΦB) through a surface S is given by
Explaination / Solution:

if dS is area of an element of any arbitrary shape and magnetic field at this element is B. The total magnetic flux through the surface is the sum of the contributions from the individual area elements.

Explaination / Solution:

The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux enclosed by the circuit.

Q7. According to Farady's law for a coil having N turns, the total induced emf is given by
Explaination / Solution:

The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux enclosed by the circuit.

induced emf for a coil having 1 turns will be

The flux of all the turns will be added up. So the induced emf for a coil having N turns will be

Q8. Coils  and  are stationary.  connected in series with one very small diwali bulb while  is connected to a battery .If the connection is suddenly snapped
Explaination / Solution:

Flux will be changed due to this current is induced momentarily

Q9. According to Lenz’s law
Explaination / Solution:

Direction of an induced emf, or the current, in any circuit is such as to oppose the cause that produce it. If the direction of the induced current were such as not to oppose then we would be obtaining electrical energy continuously without doing work, which is impossible

Q10. If the polarity of induced emf is such that it tends to produce a current which aids the change in magnetic flux that produced it, which conservation law is violated?
Explaination / Solution:

In this case we would be obtaining electrical energy continuously without doing any work.