Question

assuming a current is flowing, what increases the strength of the magnetic field of a coiled electrical wire?
straightening the wire
changing the direction of the current flow
adding more coils to the wire
stopping the current

Explanation:

• Straightening the wire reduces the magnetic field strength as the coil - like structure (which contributes to the magnetic field) is lost.
• Changing the direction of the current flow changes the direction of the magnetic field but not its strength.
• Stopping the current means there is no magnetic field (since the magnetic field of a current - carrying wire depends on the current).
• For a solenoid (coiled electrical wire), the magnetic field \(B=\mu_0nI\) where \(n = \frac{N}{L}\) (number of turns per unit length) and \(I\) is the current. Adding more coils (\(N\) increases) increases \(n\) (assuming the length \(L\) change is negligible compared to the number of turns change in a practical sense), and thus increases the magnetic field strength.

Answer:

C. adding more coils to the wire