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Exercise: 

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Que1. Fill in the blanks :

(a) A device that is used to break an electric circuit is called _______________.

(b) An electric cell has _______________ terminals.

Ans:

Que2. 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 thermo Col.

Ans:

Que3. Explain why the bulb would not glow in the arrangement shown in Fig. 12.13.

Ans: The handle of screw is made up of insulator, which does allow to current to flow. That is why the bulb is not glowing.

Que4. Complete the drawing shown in Fig 12.14 to indicate where the free ends of the two wires should be joined to make the bulb glow.

Ans: 

Que5. What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them.

Ans:  A switch is a device that either bresks the circuit or completes it. The switches used in lighting of electric bulbs and other devices in homes work on the same principle. In radio, TV, mobiles, torch and electric toys have in built switchs. 

Que6. Would the bulb glow after completing the circuit shown in Fig. 12.14 if instead of safety pin we use an eraser?

Ans: Eraser is insulator, so circuit will not complete. As a result the bulb will not glow. 

Que7. Would the bulb glow in the circuit shown in Fig. 12.15?

Ans: Both the wire are connected to only one terminal of the bulb, so current will not flow through the bulb and it would not glow. We should make a correction as follows:

Que8: Using the "conduction tester" on an object it was found that thre bulb begins to glow. Is that object a conductor or an insulator? Explain.

Ans: Since the object allows current tyo flow and completes the circuit and makes bulb to glow. It mens the object is a conductor of electricity.

Que9: Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.

Ans: Electricians frequently touch copper wires or they accidentally come in contact with live wires . Since human body is a good conductor, electricians may get shock. Rubber is an insulator. To prevent themselves from electric shock or current, the electricians use rubber gloves while repairing.

Que10: 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?

Ans: Without the help of insulators, the use of electrical took like pliers and screwdrivers will give electric shock to user. Wood and plastics are insulators and help in avoinding direct contact with electric current. When electricians touch these live electric wires with these tools covered with plastic or rubber, current does not flow in their body making safer them from any accident. 

 

12. ELECTRICITY AND CIRCUITS

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Additional-Question with solution: 

Que : What are conductors?

Ans : Materials that allow electric current to pass through them are called conductors.

Que : What are insulators?

Ans : Materials that do not allow electric current to pass through them are called insulators.

Que : Give three examples of conductors.     

Ans : Iron, copper, Aluminium etc.

Que : Give three examples of insulators.

Ans : Wood , Plastic, and rubber etc.

Que : Write a source of electricity.

Ans : Electric cell is a source of electricity.

Que : How many terminals are there in electric cell? Name them.

Ans : There are two terminals in the electric cell, positive (+ Ve) and negative (-ve).

Que : How does electric cell produce electricity?

Ans : An electric cell produces electricity from the chemicals stored inside it.

Que : Name five device in which  electric cells are used?

Ans : Electric cells are also used in alarm clocks, wristwatches, transistor radios, cameras and many other devices.

Que: What is called the filament of bulb?

Ans: The thin wire that gives off light is called the filament of the bulb.

Que: What happens when two terminals of cell is joined together?

Ans: The chemicals in the electric cell get used up very fast and the cell stops working.

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

Ans: Rubber gloves are insulators which do not allow to pass electric current through themselves. So protect from electric shock an electrician uses rubber gloves.

Que: What is the purpose of using an electric switch?

Ans: The switches used in lighting of electric bulbs and other devices in homes work on the same principle although their designs are more complex.

Que: What is switch?

Ans: A switch is a simple device that either breaks the circuit or completes it.

Que: What is an electric circuit?

Ans: A close and curve path of electric current is called an electric circuit.

Que: Give regions not to glow bulb through a complete electric circuit.

Ans:

(1) The bulb may be fused.

(2) Battery may be discharged.

(3) Circuit may be made of insulator.

(4) Switch may be disconnected/off.

Que: Give a region for a bulb to fuse.

Ans: One reason for a bulb to fuse is a break in its filament.

Que: Name some electric gadgets  in which switches are used?

Ans: Torch, Radio, Television, table fan. 

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