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Chapter Review:

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• The cell is a device in which produced electric current by chemical changes.

• A combination of two or more cells is called a battery.

• The wire gets hot when an electric current passes through it. This is the heating effect of the electric current.
• Safety device using in electric circuits is called as fuse.
• In the bulb there is a thin wire, called the filament .
• It begins to flow excess electric current in a circuit due to connect many devices to the single socket. This is known as overloading. 
• The cells of torch is connected in series.  
• Nicrome is the element made of  electric heater.
• Full Form of CFL is Compact fluorescent lamp.
• Full Form of MCB is Miniature circuit breaker.
• When the electric current is switched off, the coil generally loses its
  magnetism. Such coils are called electromagnets.
• The amount of heat produced in a wire depends on its material, length
  and thickness.

Exercise 

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1. Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position, and battery

2. Draw the circuit diagram to represent the circuit shown in.

3. shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.  

4. The bulb in the circuit shown in does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow. 

5. Name any two effects of electric current.

Answer:

(i) Heating effect, (ii) Magnetic effect.

6. When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.

Answer:

When electric current passes through a wire, it behaves like a magnet. this is the ellectric current. So, the compass needle which is a magnet, gets deflected.

7. Will the compass needle show deflection when the switch in the circuit shown by  is closed?  

8. Fill in the blanks:

(a) Longer line in the symbol for a cell represents its___________ terminal.

(b) The combination of two or more cells is called __________ a .

(c) When current is switched ‘on’ in a room heater, it___________ .

(d) The safety device based on the heating effect of electric current is called a___________ .

Answer:

(a) positive, (b) battery, (c) gets effected, (d) fuse.

9. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)

(b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)

(c) An electromagnet does not attract a piece of iron. (T/F)

(d) An electric bell has an electromagnet. (T/F)

Answer:

(a) false, (b) true, (c) false, (d) true.

10. Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

Answer:

No. Electromagnet do not attract plastic.

11. An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.

Answer:

No. The wire may not melt even if high current flows through it. So, it will not prevent the damage done by high current. 

12. Zubeda made an electric circuit using a cell holder shown in , a switch and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.

Answer:

(i) Bulb taken would be fuse.

(ii) Cell taken could be exhausted.

(iii) In cell holder, she would have connected the same terminal of the cells.  

13. In the circuit shown in

(i) Would any of the bulb glow when the switch is in the ‘OFF’ position?

(ii) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

Answer:

(i) No.

(ii) All bulb will glow at the same time.

Additional Question:

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Ques: How are two or more than two cells connected?

Ans: For connecting two or more than two cells, positive terminal of one cell is connected to negative terminal of the other cell.

Ques: What is battery?

Ans: Positive terminal of one cell is connected to negative terminal of the next cell, such a connection of two or more than two cells is known as battery.

Ques: What do you understand by heating effect of the electric current?

Ans: The wire gets hot when an electric current passes through it. This is the heating effect of the electric current.

Ques: Name two devices that work on the basis of heating effect of the electric current.

Ans: Electric iron and heater.

Ques: What material is the element made of in electric heater?

Ans: Nicrome.

Ques: What is fuse ? Give two reasons for connecting it in electric circuits.

Ans: Safety device using in electric circuits is called as fuse.

(i) It prevents the costly instruments connecting in electric circuit during overloading and short circuit.

(ii) It prevents against possibility of fire and damages of circuits.

Ques: What is overloading?

Ans: It begins to flow excess electric current in a circuit due to connect many devices to the single socket. This is known as overloading.

Ques: What is cell?

Ans: The cell is a device in which produced electric current by chemical changes.

Ques: Write the order in which cells of torch is connected.

Ans: The cells of torch is connected in series. 

Ques: Name any two insulators.

Ans: rubber and plastic.

Additional Question:

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Que: Mention the name of the two devices that work on the basis of magnetic effects of current.

Ans: The devices that work on the basis of magnetic effects of current are loudspeaker and electric bell.

Que: Name the device used days in place of eiectric fuses in electrical circuits.

Ans: The devices used in these days in place of electric fuse is MCB (Miniature Circuit Breaker).

Que: State the property of a conducting wire is utilised in making electric fuse. 

Ans: Electric fuse wire is made up of special material which has low melting point. As if high amount of current is passed, it melts to disconnect the electric circuit and prevent us from causing any damage.

Que: Name the type of mark foe which we should look at an electrical appliance before buying.

Ans: ISI mark is a mark for which we should look at an electrical appliance before buying.

Que: When does a circuit is said to be overloaded?

Ans: it is overloaded by connecting too many devices to it. When too many devices get connected, then a circuit is said to be overloaded.

Que: Why is an electric fuse required in all electrical appliance?

Ans: Electric fuse is required in all electrical appliances to prevent damage from excessive current flow and during short circuit.

Que: give the name any two electrical appliances in which electromagnets are used.

Ans: Electric fan and electrical motor are the electrical appliances in which electromagnets are used.

Que: The nails attract the pills. Comment?

Ans: When the current is passed through the wire wound on the nail, it behave as electromagnet. Due to this reason, the nails attract the pins.

Que: Name the scientist who discovered the magnetic effect of electric current.

Ans: The scientist who discovered the magnetic effect of electric current is Hans Christian Oersted.

Que: If the filament of the bulb is broken, would the circuit be complete? would the bulb still glow?

Ans: If the filament of the bulb is broken, the circuit will not be complete.

Que: Name some electric appliances where the heating effect of the electric current is used?

Ans: Some of the electric appliances where the heating effect of the electric current is used are electric heater, geyser, micro - oven, room heater, boiler etc.

Que: If the current through the coil stops flowing. will the coil remain an electromagents?

Ans: When the current through the coil stops flowing, the soil does not remain an electromagnet.