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Electro-Magnetism Questions Question
1
| a) |
Define the term "magnetic flux density". |
| b) |
An electron is moving at 107ms-1 at 90° to a magnetic field. The electron follows a circular path of radius 5×10-6m. Calculate the magnitude of the flux density. |
Question 2
A beam of alpha particles passes undeflected through a region of space in which there are a magnetic field (of flux density 5×10-2T) and an electric field (of field strength 750Vm-1) at 90° to each other. Calculate the speed of the particles. |
Question 3
| The charge to mass ratio of an electron is 1·76×1011Ckg-1. Calculate the time period of the circular motion of an electron in a magnetic field of flux density 0·1T. |
Question 4
A proton enters a uniform magnetic field of flux density, B = 0·1T with a velocity of 104ms-1 at 60° to the flux lines. It follows a helical path.
Calculate |
| a) |
the time taken to complete one revolution of the helical path |
| b) |
the distance moved parallel to the flux lines during this time |
| c) |
the kinetic energy possessed by the proton when it is in the magnetic field (mass of a proton = 1·67×10-27kg). |
Question 5
| A very long straight wire lies along the z axis and carries a current, I which flows in the positive z direction in a vacuum (see diagram below). |
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| Two flux densities BA and BB are measured at points A (x = 0, y = 10cm, z = 0) and B (x = 0, y = 20cm, z = 0) |
| a) |
In which direction do BA and BB act? |
| b) |
If I = 1·5A, calculate the magnitude of BA. |
| c) |
What value of current would produce a flux density at point B equal to the value you have just calculated for BA? |
| d) |
Find the magnitudes and directions of the flux densities BC and BD at the points C and D
C has co-ordinates x = 4cm, y = 4cm, z = 0cm
D has co-ordinates x = 4cm, y = 4cm, z = 10cm |
Question 6
A piece of wire is 8cm long and is placed at an angle of 30° to a magnetic field of flux density 0·5T. Calculate the magnitude of the force acting on the wire when a current of 500mA flows through it.
Name the rule used to predict the direction of the force on the wire. |
Question 7
| a) |
Explain why a moving coil galvanometer must have control springs (or something equivalent to control springs). |
| b) |
How is a moving coil galvanometer made to have a high current sensitivity? |
| c) |
A moving coil galvanometer could be made without a soft iron cylinder. What would be the main disadvantage of a meter without a soft iron cylinder? |
Question 8
Two straight wires are parallel to each other and 5cm apart. Wire A-B has a current of I1 = 5A flowing through it and wire C-D has a current of I2 = 20A flowing through it (see diagram below).
What is the magnitude and direction of the electro-magnetic force acting on wire A-B? |
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