MFHS
Motors And Generators
Revision
1) Two parallel wires of length 0.25 m carry a current of 0.5 A and 2.5 A.
a) Find the force between the wires, if they are 0.05 m apart.
b) If the wires are attracting each other, do the currents run in the same direction or opposite directions?
2) Find magnitude and direction of the force acting on a wire of 50 cm length, carrying a current of 5 A at 60o to a magnetic field of 0.4 T.
3) Draw an electric motor. Explain, in which of the indicated positions is the torque maximum and in which is it minimum?
4) Find the torque in three positions indicated in the above drawing, given that the coil of wire has 500 turns, the current is 4 A, the magnetic field strength is 0.5 T, the width (depth of coil into the page) of the coil is 5 cm and the radius indicated in the drawing is 4 cm.
5) Describe and explain two improvements to the above motor.
6) If the set up in question three would be used as a generator, find the magnetic flux in the three above positions.
7) What is another word for flux density?
8) An electric drill gets stuck. Even though there is a current flowing through the coil, it does not move. Is the electric current through the coil now greater or smaller than when the drill is in normal operation? Explain, naming relevant laws.
9) How many coils are needed on the secondary coil of a transformer that has 500 coils on the primary coil to produce a secondary potential difference of 20 V from a primary potential difference of 240 V?
10) How does an AC – Motor work?
