Well known magnetic field relationships are shown at right.
| Click the equations in the panel at right for their origin and a brief explanation.... and click again to return. |
1 A simple DC electric motor model has a rectangular coil of 50 turns which is free to rotate in a uniform electric field as shown.
a The coil is 5 cm on a side.
i Find the size and direction of the forces acting on each side of the coil.
ii Calculate the maximum torque applied to the coil in newton meters and state the coil position in which this occurs.
b Outline four ways in which the torque could be increased in a real case.
2 Charged particles enter an evacuated chamber containing a uniform vertical magnetic field from the left as shown.
i Sketch possible paths for a proton and an electron in the magnetic field - explaining how you arrived at your answers.
ii How would your answers be modified if the chamber contained some air?
b A proton has a velocity of 3x105 m/s and the field is 0.2 T.
i Find the radius of the path.
ii How would the radius be altered if the particle were an alpha particle of the same kinetic energy?
3a Two very long parallel wires A and B carry currents of 10 amps and 20 amps respectively. The wires are separated by 25 cm.
i Find the strength of the magnetic field of wire A in the location of wire B.
ii find the size and direction of the force per unit length on each wire.
ii What important definition is based on your calculations for Part ii of this question?
b A long solenoid has a radius of 2 cm and a length of 50 cm. It is wound from 200 meters of fine copper wire.
i Find the number of turns on the solenoid.
ii Find the magnetic field strength in the middle of the solenoid if it carries a current of 0.5 Amperes.
iii How would the field strength be changed if the coil were compressed along its length to a new length of 25 cm without changing the number of turns, the radius or the current?