Chapter 12 Electricity and Circuits Solutions
Question - 1 : - Fill in the blanks:
(a) A device that is used to break an electric circuit is called ………………………… .
(b) An electric cell has ………………………… terminals.
Answer - 1 : -
(a) switch
(b) two
Question - 2 : - 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.
Answer - 2 : -
(a) True
(b) False
(c) False.
Question - 3 : - Explain why the bulb would not glow in the arrangement shown in Fig. 12.7.
Answer - 3 : -
We know that a bulb lights up only when bulb and wire form a complete path, which starts at one terminal of the electric cell and ends at the other terminal. Here in this arrangement, the circuit is not completed. The handle of the screw driver is made of some material which is an insulator. That is why the bulb will not glow.
Question - 4 : - Complete the drawing shown in Fig. 12.4 to indicate where the free ends of the two wires should be joined to make the bulb glow.
Answer - 4 : - 
Question - 5 : - What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them.
Answer - 5 : -
A switch is a simple device that either breaks the circuit or completes it. Hence we use electric switches in order to either
- stop an electrical gadget in function when required, or
- to start an electrical gadget when needed.
Some electrical gadgets that have switches built into them are electric iron, table fan, television set, radio, etc.
Question - 6 : - Would the bulb glow after completing the circuit shown in Fig. 12.8, if insteajl of safety pin we use an eraser?
Answer - 6 : -
No, the bulb will not light up. This is because an electric bulb lights up only when circuit is completed and eraser is a non-conducting material.
Question - 7 : - Would the bulb gow in the circuit shown in Fig 12.9?
Answer - 7 : -
In this circuit, the bulb is connected through a woollen thread with the negative terminal of electrical cell. Since woollen thread is not a conductor of electricity, it will not allow the electricity to flow through it that is from bulb to electrical cell. Thus the circuit remains incomplete and hence the bulb will not light up.
Question - 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.
Answer - 8 : -
The material of that object is a conductor. Because with this object bulb lights up showing that electricity is flowing in the circuit, i.e., the circuit is complete. This is possible only if the material of the object allows the electricity to pass through it and we know only conductors allow the electricity to pass, thus the material of the object must be a conductor.
Question - 9 : - Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.
Answer - 9 : -
While carrying out electrical repairs one must wear rubber gloves. This is because our body is a good conductor of electricity, and if there is any contact of naked wire with our naked hand it will be very dangerous. And if we are with rubber gloves on our hands, the rubber being an insulator will protect us from electric shock.
Question - 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?
Answer - 10 : -
With screwdrivers, the electrician has to touch naked wires and screws in which electricity is flowing. If the screwdriver will have no handle made of plastic or wood, the electricity will flow through the screwdriver to his body, which is itself a good conductor of electricity and he has to face an electric shock. If handles are coated with wood or plastic, which are insulators, that will check this flow of electricity, thus making him safe from electric shock.