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# Chapter 12: Electricity and Circuits (Solutions)Posted on : 20-06-2018 Posted by : Admin

1. Fill up the blanks in the following:

(i) A device that is used to break an electric circuit is called switch.

(ii) An electric cell has two terminals.

2. State which of the following statements are True and False

(a) Electric current can flow through metals. (True)

(b) Instead of metal wires, a jute string can be used to make a circuit. (False)

(c) Electric current can pass through a sheet of thermo Col. (False)

3. Explain why the bulb would not glow in the arrangement shown below.

Answer: The bulb in the given arrangement does not glow as the circuit is broken due to the presence of plastic tester holder in the circuit path. Plastic is a bad conductor of electric current and the electric current cannot pass through these objects.

4. Complete the drawing shown below to indicate where the free ends of the two wires should be joined to make the bulb glow.

Answer: The broken circuit in the given drawing must be completed to make the bulb glow.

To complete the circuit, one end of the wire from to the pin 1 must be connected to the electric cell terminal and another end of the wire from pin 2 must be connected to bulb terminal. Now the circuit is complete and the bulb will glow.

5. What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them.

Answer: Electric switch is a simple device that is used to either open or close the electric circuits to turn on or turn off the electrical appliances. When the switch is turned ON, it will allow the electric current to flow through it and when the switch is turned OFF, it will not allow any electric current to pass through it.

Some electric appliances which have switches built into them are mixer-grinder, battery charger, iron-box, hair dryer, rice cooker, washing machine etc.

6. Would the bulb glow after completing the circuit shown below if instead of safety pin we use an eraser?

Answer: No, the bulb would not glow if the circuit is completed with an eraser instead of safety pin. This is because rubber is bad conductor if electricity unlike safety pin which is a good conductor of electricity

7. Would the bulb glow in the circuit shown below?

Answer: No the bulb in the circuit would not glow because wires from both the terminals of the battery are connected only to one terminal of the bulb. For the bulb to glow the wires from both the terminals of the battery must be connected to both the terminals of the bulb..

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: The object must be definitely an insulator as it allows the electric current to pass through it. And hence when a conduction tested is used on the object, the bulb started to glow..

9. Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.

Answer: Human body is the good conductor whereas rubber gloves are bad conductors of electricity. While repairing an electric switch, if the electrician comes in contact with the electric current it may lead to an accident. If the electrician uses rubber gloves, he would be safe as the rubber gloves do not allow electric current to pass through them. Hence an electrician uses rubber gloves.

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: Because plastic is the bad conductor of electricity, the handles of the tools like screwdrivers and pliers used by electricians usually have plastic or rubber covers on them. Bad conductors of electricity do not allow electric current to pass through them. And finally the person holding and working with these tools will be safe.

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