In a circular loop of wire lying on a horizontal floor, the current is constant and, to a person looking downward, has a clockwise direction. The accompanying magnetic field at the center of the circle is directed a) horizontally and to the east. d) parallel to the floor. b) horizontally and to the north. e) vertically downward. c) vertically upward.

e) vertically downward.

Explanation:

Direction of magnetic field due to a current carrying circular coil is known from the screw rule or right hand thumb rule.

Screw rule states that if we turn the screw driver in the direction of current in the coil , the direction of movement of rod of screw driver gives the direction of magnetic field.  if we turn the screw driver clockwise , it will move forward . That means magnetic field will be towards vertically downward direction .

Thumb Rule states that if we hold our closed fist such that the folded four fingers are in the direction of circular current , our thumb will show the direction of magnetic field. This also shows that magnetic field will be vertically downwards.

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.