**Question 1**

a) | Define the term "magnetic flux density". |

b) | An electron is moving at 10^{7}ms^{-1} at 90° to a magnetic field. The electron follows a circular path of radius 5×10^{-6}m. 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^{-2}T) 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 1·76×10^{11}Ckg^{-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 10
^{4}ms^{-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^{-27}kg). |

**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). | |

Two flux densities B_{A} and B_{B} are measured at points A (x = 0, y = 10cm, z = 0) and B (x = 0, y = 20cm, z = 0) | |

a) | In which direction do B_{A} and B_{B} act? |

b) | If I = 1·5A, calculate the magnitude of B_{A}. |

c) | What value of current would produce a flux density at point B equal to the value you have just calculated for B_{A}? |

d) |
Find the magnitudes and directions of the flux densities B
_{C} and B_{D} at the points C and DC 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 I
What is the magnitude and direction of the electro-magnetic force acting on wire A-B?_{1} = 5A flowing through it and wire C-D has a current of I_{2} = 20A flowing through it (see diagram below). |