Which of the following is true of the magnetic field produced by a current in a long, straight wire?

Question

(A) The field is uniform.
(B) The field increases in strength as the
distance from the wire increases.
(C) The field lines are directed parallel to the
wire, but opposite to the direction of the
current.
(D) The field lines are directed radially
outward from the wire.
(E) The field lines form circles about
the wire.

Answer 1

(A) No, the field strength decreases with distance from the wire.

(B) No, see A

(C) No, see E

(D) No, see E

(E) Correct

Hold out your right hand, thumb extended. If your thumb is in the direction of the positive current, the fingers of your right hand curl around your thumb in the same way that magnetic field lines circle the wire.

Answer 2

The formula for the field around a long straight wire is B=µ/2π*I/d and these questions can be answered in terms of this.
A) The field is not uniform. The further away you get, the weaker the field;
B) See above
C) Field lines are circular around the wire. Use the right-hand grip rule. Thumb is direction of (conventional) current, field lines move in the direction of the curl of your fingers.
D)See above
E) Correct

Answer 3

The magnetic field from a such current-carrying wire wraps around the wire in circular loops, decreasing in magnitude with increasing distance from the wire.