Question

For Fleming’s left-hand rule, write down the three things that are $90{}^\circ$ to each other, and next to each one write down the finger of thumb that represents it.

Answer 1

Hint: To solve this question we will need to learn the concept of Fleming’s left hand rule, what is it useful for and then we will see which are the factors that are perpendicular to each other.

Complete answer:
First of all we'll know for what Fleming's left hand rule is useful: When a current-carrying conductor comes under an influence of magnetic field, there will naturally be a force acting on that conductor. Fleming’s left hand rule is an accurate way to find the direction of force or motion of any conductor in an electric motor when the magnetic field direction and current direction of that conductor are known.

This rule was originally developed in the late 19th century, by John Ambrose Fleming, an English electrical engineer. The left-hand rule uses the thumb, the index finger, and the middle finger of the left hand. The hand is held with the palm up, the thumb and middle fingers aligned as though they were joined end-to-end, and the index finger held out in a perpendicular manner.

The instructions for this rule is as follows:
Thumb: The thumb is a representation of the direction of thrust or force on the conductor.
Index Finger: Also known as the forefinger, is representative of the direction of the magnetic field.
Middle Finger: Also known as the center finger, it represents the direction of the current.

Therefore the three perpendicular factors are force, magnetic field and current represented by thumb, index finger and middle finger respectively.

Note:One must take note that Fleming’s left hand rule is used for electric motors whereas Fleming’s right hand rule is used for electric generators. In an electric generator motion and magnetic field leads to the creation of electric current and so, the right hand rule is used.