Question

a. This is a prediction. Do not carry it out yet. Suppose you were to close the switch and bring the north pole of a cow magnet up under the wire, as in the diagram below (while the switch is closed). Z (1) What is the approximate direction of the net magnetic field of the magnet near the wire? Explain your reasoning. if possible Ho a catter (ii) Which direction, if any, would the wire move? Record your prediction for the direction of motion of the wire. Explain your reasoning for your choice of direction or explain why it wouldn't move. band Ć. 2 b. Carry out the experiment in part a. With the switch closed, bring the magnet up under the wire. Observe the direction of motion of the wire. Do not hold the switch down for long periods of time, or you will run down the battery quite quickly. The motion may be small, but you will be able to see it. Record the direction of the motion. Draw the direction of the field, the direction of the current and the direction of the force on the wire in the picture above.

Answer 1

(a) - (i)

fo N X INI

In a bar magnet , magnetic field lines start from North pole and end at South pole as shown in figure.

Hence as shown in figure direction of net magnetic field near wire is from bottom to top of page .

If we consider cartesian coordinate system as shown in figure, direction of magnetic field is in +z-axis direction.

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(a) - (ii)

Z BP BY tu Y IN X Field Thumb - Motion Current 1 T

Fleming's left hand rule is applied to get the direction of force when applied magnetic field direction is perpendicular to current direction in wire. As shown in figure , if we stretch our left hand middle finger, index finger and thumb in a such a way each finger is mutually perpendicular to others , then middle finger represents the direction of current, index finger represents the direction of field and thumb shows the direction of force.

If we apply the Fleming's left hand rule in our experiemnt , as per the direction of current and magnetic field ( see figure ) , we get force in the direction into the page or as per the coordinate system the force is in -x axis direction.

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When the magnet is reversed , magnetic field direction is top of page to bottom of page . i.e. in -z axis direction . Direction of current is not changed . Then By applying Flemings left hand rule , we see that the direction of force is out of page or +x axis direction.