Question

8. The coils of a solenoid are stretched so that the length of the solenoid is twice its original length. Assuming the same current is passed though the solenoid before and after it is stretched, how does the magnetic field inside the solenoid change, if at all, as a result of the stretching? a) The magnetic field after the stretching is one-fourth the value it was before stretching. b) The magnetic field after the stretching is one-half the value it was before stretching. c) The magnetic field after the stretching is the same as the value it was before stretching. d) The magnetic field after the stretching is twice the value it was before stretching. e) The magnetic field after the stretching is four times the value it was before stretching.

Answer 1

The magnetic field inside the solenoid remains the same after the stretching.

Step-by-step explanation:

The magnetic field inside a solenoid is directly proportional to the number of turns of wire and the current passing through it, and is inversely proportional to its length. When the length of the solenoid is doubled while keeping the current the same, the magnetic field inside the solenoid remains the same. This is because doubling the length of the solenoid is compensated by halving the magnetic field strength per unit length.

Therefore, the correct answer is c) The magnetic field after the stretching is the same as the value it was before stretching.

Answer 2

b) The magnetic field after the stretching is one-half the value it was before stretching

Step-by-step explanation:

magnetic field in a solenoid = μ n i

where μ is permeability , n is no of turns per unit length and i is current

= μ N i / L where N is total no of turns in the whole length L of solenoid.

Now μ , N , i are constant

B = K / L

So

B is inversely proportional to length of solenoid. If L becomes two times , B will become half .

Option ( B ) is correct .