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

Answer 1

Adding more coils to the wire.

Reason: for a solenoid the magnetic field strength increases with the number of turns (and with the current). Straightening the wire reduces the concentrated field, changing the direction of the current reverses the field direction but not its magnitude, and stopping the current removes the field.