## P and Q represent two straight wires carrying equal current (I) in a direction perpendicular to the plane of the screen outwards. K is the midpoint of the line joining P and Q. The image shows the magnetic field lines around the wire. But the direction of the magnetic field is not marked.

## (a) Draw the above image and mark the direction of the magnetic field.

## (b) If the current in the wires is increased, how will the strength of the magnetic field around P and Q change? Draw the magnetic field lines around P and Q to represent this change.

## (c) If B is the magnetic field at point K due to the current in wire P, what will be the magnetic field due to P and Q at the midpoint K? Give a reason for your answer.

## (d) If B is the magnetic field at point K due to the current in wire P and the current in wire Q is reversed, what will be the magnetic field at midpoint K?

**
Answer:
**

(a)

(b) The strength of the magnetic field around P and Q will increase.

(c) Zero.

The magnetic fields at point K due to current in the wires P and Q are equal in magnitude but opposite in direction. The two fields cancel each other.

(d)

If the
**
current in Q is reversed
**
, the direction of the
**
magnetic field due to Q at K will reverse
**
, to be in the
**
same direction as P
**
.

Thus, the two magnetic fields will be added up to
**
2B
**
.