Fill in the blanks.
(A) A device that is used to break an electric circuit is called __________.
(B) An electric cell has ___________ terminals.
(A) A device that is used to break an electric circuit is called switch.
(B) An electric cell has two terminals.
Mark 'True' or 'False' for following statements.
(A) Electric current can flow through metals.
(B) Instead of metal wires, a jute string can be used to make a circuit.
(C) Electric current can pass through a sheet of thermocol.
(A) True. Metals are good conductors of heat and electricity.
(B) False. A jute string is a bad conductor of electricity.
(C) False. Thermocol is an insulator.
Explain why the bulb would not glow in the arrangement shown in figure.
The bulb would not glow in the given arrangement because upper portion of screw driver is made of bakelite or any other insulator. Hence, the circuit is incomplete.Q 4.
Complete the drawing shown in figure to indicate where the free ends of the two wires should be joined to make the bulb glow.
One free end should be connected to the lower terminal of bulb and other free end should be connected to the positive terminal of the electric cell.
What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them.SOLUTION:
An electric switch is a simple device that is used to either break the electric circuit or to complete it.
Some electrical gadgets that have switches built into them are: mobile phones, T.V., laptop, washing machine etc.
Would the bulb glow after completing the circuit shown in figure if instead of safety pin we use an eraser?
No, the bulb would not glow after completing the circuit if an eraser is used instead of safety pin. Because eraser is an insulator, so, it cannot conduct electricity.Q 7.
Would the bulb glow in the circuit shown in figure?
No, the bulb would not glow in the given circuit because one of the terminals of bulb is not connected in the circuit. The base of the bulb and the metal tip of the metal case are the two terminals of the bulb. In this circuit base of the bulb remains disconnected.Q 8.
Using the "conduction tester" on an object it was found that the bulb begins to glow. Is that object a conductor or an insulator? Explain.SOLUTION:
That object is a conductor. The bulb of conduction tester glows on touching this object which means that conduction is happening through this object, i.e., electric current is flowing through it.Q 9.
Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.SOLUTION:
An electrician should always use rubber gloves while repairing an electric switch because rubber is an insulator. So, it can prevent the electrician from getting an electric shock, in case he touches the live wire.Q 10.
The handles of the tools like screwdrivers and pliers used by electricians for repair work usually have plastic or rubber covers on them. Can you explain why?SOLUTION:
The handles of the tools like screwdrivers and pliers used by electricians for repair work usually have plastic or rubber covers on them because plastic and rubber are insulators. Electric current cannot conduct through insulators. So, electricians would not get an electric shock while repairing.