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