s in the position shown, there is s cunent,,thregh 19 View of end wie ead insula

Question

s in the position shown, there is s cunent,,thregh 19 View of end wie ead insulation has been rippe from erwer hlf The coil is manually started spinning so that it rolates clockwis a. During which portions of the cycle does the coil form a complete cirt with e battery such that there is a current through the wire of the coil? The current results in a magnetic moment that interacts with the magnetic field of the net. Will the interaction tend to increase or to decrease the angular speed of the coil? Explain. b· The coil is manually started spinning so that it rotates counterclockwise: During which portions of the cycle does the coil form a complete circuit with the The current results in a magnetic moment that interacts with the magnetic field of the magnet. Will the interaction tend to increase or to decrease the angular speed of the coil? Explain. Check that the behavior of your motor is consistent with your answers Consider the following questions about the motor * Why was insulated wire used for the coil? Would bare wire also work? Explain 4. Would you expect the motor to work if the leadsto the cire sripped completst Explain. reversing S. Predict the effect on the motor of () reversing the leads to the orientation of the magnet. Check your predictions. CPrentice Hall, Inc Fint Edition, 2002 y Physics

Explanation / Answer

For the given problem

3. a. the coil is manually started to rotate clockwise

from the gicen view of the terminals of the coil

for clockwise motion , current would be available in the coil for the first half cycle of its rotaional motion and then not available for the next half cycle of its motion

for clockwise rotation

initially the north pole of the coil moves towards the north pole of the magnet, so this will cause a repulsive force, slowing down the coil, but then when the coil reaches the quarter cycle, the north ppole of the magnet moves away frpm the north pole of the coil, and hence the coil speeds up to its previous speed

after half cycle, ther is no current in the circuit and the coil rotates to its initial position to complete the cycle at constat speed (ignoring resistance of the wires)

b. for CCW rotation

from the gicen view of the terminals of the coil

for counterclockwise motion , current would be available in the coil for the second half cycle of its rotaional motion and then not available for the first half cycle of its motion

for counterclockwise rotation

for the first half cycle the coil moves at constant speed

then the north pole of the coil moves towards the north pole of the magnet, so this will cause a repulsive force, slowing down the coil, but then when the coil reaches the three quarter cycle, the north pole of the magnet moves away frpm the north pole of the coil, and hence the coil speeds up to its previous speed

4. bare wire can also work for the experiment, but insulated wire is used for safety purposes, as there can be an experience of a shock due to accidental touching of the wire while the experiment is going on

if the lead coils were completely stripped, gthen for the half cycle, when the coil rotates with constant speed, it would instead follow the same trend of speeding down and up

5. reversing lead to the battery and reversing polarity of the magnet will have no effects onthe motor rotation expect changing the reltive position of the free rotation half and slowing down/speeding up half in the full time period of the motor

4. for the gerentator, if the coil is moved by external agent

a. when the coil strarts rotation, the needle will deflect to one side, and change its direction when half cycle of rottion of the coil is complete

b. for rotaiton is opposite direction, the deflection sign will be opposite than the previous case

c. if the poles were reversed, then again the deflection would be opposite to the case 1

2. when the coil is not given energy to rotate it will stop after a while depending on th eenergy provided to it. faster it was rotating, longet it will take to stop

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