Q. What is direction of the current?

The path of the magnetic field at the centre of a horizontal current-carrying loop of wire is straight downward. The magnetic field is affected by the current in the loop. What is direction of the current?

Answer:

Specified a conducting wire in the form of a loop and given the current in that loop we can apply the right hand rule to determine the direction of the magnetic field at the centre of that loop. The entire we have to do is to curl the fingers of the right hand around in the direction of the current and the extended thumb of s the cupped right hand will point in the direction of the magnetic field inside at the centre of the loop.

Interestingly sufficient this procedure is reversible. That is if we aren't told the direction of the current but we know the direction of the magnetic field at the centre of the loop all we have to do is point the extended thumb of the cupped right hand in the direction of the magnetic field at the centre of the loop and the fingers will indicate the direction in which the current must be flowing around the loop to produce such a magnetic field. In the situation at hand pointing the thumb downward (toward the centre of the earth) we find that the fingers curl in the clockwise direction, as viewed from above. Therefore the current is clockwise in the loop as viewed from above. This is one of those trouble in which we are given some information about the effect of something (the effect of the current in this case) and asked to find something about the cause (the current itself in this case). The right hand rule approachs in "handy" for this one (pun intended).