Oh! Why Don't I Have Three Hands !

In this last part of unit 5, we deal with anything related to magnet. Many of you are confused with the Right-hand and the Left-hand rule. Well, it would be clearer if you can divide them into 3 main categories.

1. Magnetic-fields production :-

In this section, you use the grasping hand rule ( right hand only)
(a) Straight wire carrying a current : use thumb to follow the flow of current in the wire and the closing fingers the direction of the field lines (no north or south poles).
(B) A coil or solenoid (including Eddy current): Use the closing fingers to follow the flow of current ( because it is circular) and the thumb will point to the north pole. (imagine you are inside the bar magnet).

2. Producing motion

In this section, a power source is provided, so it is a motor. Electricity is doing the work for you, so you don't need a strong hand, you left hand will do. So, it is the Flemming's Left Hand Rule here. A current carrying conductor in a magnetic field will produce a magnetic force acting on the conductor. An electron beam moving in a magnectic field will produce a magnetic force acting on the individual electron and this force provides the centripetal force to make the electrons moving in a circle. BUT, a current carrying straight conductor alone will not produce a force in its own magnetic field. It must be in someone else's magnetic field for the force to be produced.

3. Current producing action

Here,mechanical energy is converted to electricity. You need a strong hand to produce electricity,hence the right hand. So you use Flemming's Right Hand Rule for this. The situations include flying aeroplane (horizontally and north-south direction) cutting through the vertical components of the Earth's magnetic field. No emf will be produced for cutting the horizontal components because there is no change in the flux line cutting the wing.

Hope the above will help.