Question

The image shows copper wire coiled around an iron nail and connected to a battery to create an electromagnet.

Which will increase the strength of this electromagnet?



A.
using a battery with lower voltage

B.
using a larger nail

C.
using a larger switch

D.
adding another battery to the circuit

Answer 1

it would be b or d

Answer 2

The formula for the strength of the field \(B\) of a solenoid of length \(L\) and round an iron core with N turns is
\[B=\mu \frac{NI}{L}\]
So increasing the current \(I\) by adding a battery in series will increase the strength of the electromagnet \(B\).

Answer 3

Sorry I meant:
So increasing the current \(I\) by adding a battery in PARALLEL will increase the strength of the electromagnet \(B\).

Answer 4

If we are to connect the battery in series, the strength will also increase:
\[B=\mu \frac{NV}{LR}\].

See here: http://physics.stackexchange.com/questions/60079/does-an-electromagnet-increase-in-strength-more-by-voltage-or-wire-turns

Answer 5

But why are the other answers incorrect:

A: A lower voltage battery with the same current will mean that \(B\) decreases since \(B=\mu \frac{NV}{LR}\).

B: Using a larger nail means less turns can be made with the same length of wire, so again \(B\) decreases

C: As far as we are concerned, changing the size of the switch has a neglible effect on the strength of the electromagnet.