As we know that human body is a good conductor of electricity. So, it is necessary to prevent it from electric shocks.
On the other hand, plastic and rubber are insulators that do not allow electricity to pass through them. Hence, electricians use screwdrivers and pliers which have plastic or rubber covering on them for repair the work.

An electrician should use rubber gloves while repairing an electric switch because rubber is an insulator that does not allow electric current to pass through it. Thus, it prevents his body to get electric shocks.
On the other hand, human body is a conductor of electricity, so it is necessary to prevent it from electric shocks.

Since, eraser is an insulator that means itis a bad conductor of electricity. So, conduction of electric current is not possible. Thus, if instead of safety pin, an eraser is used, bulb will not glow.

Switch is a simple device that is used to either break the electric circuit or to complete it. With the help of a switch, we can use an appliance according to our desire.
The switches used in lighting of electric bulbs and other devices in home works on the same principle.
Some electrical gadgets that are switches built into them are as follows:
(i) Torch
(ii) Table fan
(iii) Television set
(iv) Radio
(v) Electric iron

To complete the circuit, we must join the one end of the wire with the free end of cell. The other end of wire must be connected with the bulb. Now, the bulb will glow.

Materials through which electric current cannot flow are called as insulators. For example: rubber.

Materials used in the electric circuit should be good conductors of electricity that allow electricity to pass through them such as metals (aluminium, copper, iron, etc).

The glowing part of an electric bulb is its filament.

A fused bulb does not glow because in a fused bulb, the filament of bulb burns up and connection is broken or incomplete, so the current cannot flow.

An electric switch is a device used to complete or break an electric circuit. Usually, it is manually operated.
Purpose of using electric switch: In 'ON' position, the switch allows the current to flow through the circuit. Thus, the circuit becomes a closed circuit. In 'OFF' position, the switch does not allow current to flow through the circuit. Thus, the circuit becomes an open circuit.
Examples: Electrical appliances such as fans, electric lamps, washing machines, juicer and mixer, TV radio, etc, have switches.

The arrangement of bulb should be such that positive terminal of a battery touches the base of the bulb. When switch ON, bulb will glow.

(a) The direction of current will be from Q to P in A and direction of current will be from P to Q in B. Because direction of current is always from positive terminal to negative terminal of the cell or battery.
(b) Yes, the bulb will glow in both the cases because to glow the bulb, we just need to complete the circuit.
(c) No, the brightness of the bulb never depend upon the direction of current passing through it.