10. Electric Current and its Effects

Q1. Draw in your notebook the symbols to represent the following components of electrical circuits:

Ans:

1. Connecting wires:
2. Switch in the ‘OFF’ position: 
3. Bulb:  
4. Cell:  
5. Switch in the ‘ON’ position:  
6. Battery:  

Q2. Draw the circuit diagram to represent the circuit shown in Fig.10.21.

Ans:

Q3. Fig.10.22 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.

Ans:

Q4. The bulb in the circuit shown in Fig.10.23 does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

Ans:

1. The bulb in the circuit is not glowing because the cells are not connected correctly.
2. To make the bulbs glow, negative of one cell should be connected to the positive of another cell.

Corrected diagram is:

Q5. Name any two effects of electric current.

Ans:

The two effects of electric current are:

1. Heating effect of electric current.
2. Magnetic effect of electric current. 

Q6. When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.

Ans:

1. When a current is switched on through the wire, the wire acts like a magnet.
2. This is called magnetic effect of electric current.
3. So, when a compass needle is kept near this wire, it gets influeced by the magnetic field around the wire.
4. Hence, it is deflected from its north-south position.

Q7. Will the compass needle show deflection when the switch in the circuit shown by Fig.10.24 is closed?

Ans:

1. The given figure, has no current source.
2. Hence, even if the witch in the circuit is closed, there will be no electric current.
3. So, the wire will not behave like a magnet in absence of current & the needle will not deflect.

Q8. Fill in the blanks:

Ans:

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

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

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

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

Q9. Mark ‘T’ if the statement is true and ‘F’ if it is false:

Ans:

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

(The negative terminal of one cell should be connected to the positive terminal of another cell.)

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

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

(A electromagnet acts like a magnet when current passes through it)

(d) An electric bell has an electromagnet. = T

Q10. Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

Ans:

1. No, an electromagnet cannot be used to separate plastic from garbage.
2. An electromagent acts as a magnet as it works on the principle of magnetic effect of electric current.
3. It attracts only metals. As plastic is not a metal, an electromagnet cannot attract it.

Q11. 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.

Ans:

1. No, I would not agree.
2. A fuse is a safety device, which breaks the circuit when it gets heated & prevents excessive current from flowing.
3. If the wire replaces the fuse,  the wire has high melting point & so it will not break the circuit when excessive current will pass through the circuit.
4. This will damage the circuit & electric appliances & may cause electric fire.

Q12. Zubeda made an electric circuit using a cell holder shown in Fig. 10.4, 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.

Ans:

1. The bulb is burnt out or fused.
2. The wires may be loosely connected.
3. The cell terminals may not be connected correctly.
4. The cells may be used up.
5. Switch may not be functioning.

Q13. In the circuit shown in Fig. 10.25: (i) Would any of the bulbs glow when the switch is in the ‘OFF’ position?

Ans:

1. No, none of the bulbs will glow when the switch is off.
2. The circuit is open, so current cannot flow. Hence none of the bulbs will glow.

(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?

• When the switch is on all the bulbs will glow together at once.
• This is because the circuit will be complete and current will flow.
• The bulbs are connected in series with the battery & switch.