Question

State Right hand screw rule and right hand thumb rule. Why are these rules used?

Answer 1

In mathematics and physics, the right-hand rule is a common mnemonic for understanding orientation of axes in 3-dimensional space. Most of the various left- and right-hand rules arise from the fact that the three axes of three-dimensional space have two possible orientations. 


If a current carrying conductor placed in a magnetic field, it experiences a force due to the magnetic field. On the other hand, if a conductor moved in a magnetic field, an emf gets induced across the conductor (Faraday's law of electromagnetic induction).
John Ambrose Fleming introduced two rules to determine the direction of motion (in motors) or the direction of induced current (in generators). The rules are called as Fleming's left hand rule (for motors) and Fleming's right hand rule (for generators).

Answer 2

Fleming's Right Hand Thumb Rule

according to the Fleming's right hand rule hold the thumb the fourth finger and the centre finger of your right hand at right angles one another. I just your hand in fact is that for single quotes in the direction of magnetic field and Thumb. In the direction of motion of the conductor then the direction in which Centre finger. Give the direction of induced current in the conductor.

I don't know about screw rule.