Question

5. This diagram shows two identical coils next to each other. Point A is to the left, and a straight line could be drawn starting from point A through the exact middle of both coils. The left coil is connected to a battery through an open switch as shown. The arrow on the left coil shows the direction in which electric current flows through that coil. At the moment shown, draw the galvanometer needle with its correct position in the diagram above. a. At a certain moment t = 0 seconds, the switch is closed. At the moment the switch is closed, draw an arrow in the box below to represent the direction of the magnetic field at point A that is due to the left coil. If there is no magnetic field, write "zero magnetic field." b. At the moment the switch is closed, draw (below) the first position to which the galvanometer needle moves. Note: There is more than one possible answer; however, it must be consistent with your other answers. c. d. The switch is left closed for five seconds so the battery stays connected to the left coil during that period. Draw the approximate position of the galvanometer needle at 13 seconds

Answer 1

Given that (a) As switch is closed, there is no magnetic field with first coil and hence flux link to second coil. So galvanometer shows zero. (b) If switch is closed at t = 0, current �i� in left coil is zero. It should grow up with time, hence magnetic field at A is zero. (c) At the moment switch is closed, magnetic field in left coil produces flux, this flux is linked with second coil and due to change in flux an induced emf produces in second coil. The direction of induced emf produces in such a way it opposes the original cause of producing it. Hence direction of current in right coil is opposite to current in the first coil. \r\n So the needle of Galvanometer defect towards left. i.e. towards negative. (d) As time elapsed, current in left coil reaches its maximum value, hence rate of change in current di/dt decreases as a result, the induced current in right coil also decreases. Hence the needle of Galvanometer move towards zero.