>

## Solutions of Magnetic Effects of Electric Current Lakhmir Singh Manjit Kaur VSAQ, SAQ, MCQ, HOTS, and LAQ Pg No. 113 Class 10 Physics 1. What name is given to the device which automatically cuts off the electricity supply during short-circuiting in household wiring?

→ Electric fuse is the name given to the device which automatically cuts off the electricity supply during short-circuiting in household wiring.

2. What is the usual capacity of an electric fuse used (i) in the lighting circuit, and (ii) in the power circuit, of a small house?

→ i) the usual capacity of an electric fuse used in the lighting circuit is 5A.
ii) in the power circuit of a small house the usual capacity of an electric fuse used is 15A.

3. Give the symbol of an electric fuse used in circuit diagrams. 4. State whether the following statements are true or false:
(a) A wire with a green insulation is usually the live wire.
(b) A miniature circuit breaker (MCB) works on the heating effect of current.

→ (a) False
The green wire indicates the wire is grounded.
(b) False
A miniature circuit breaker (MCB) works on the electromechanical effect of current.

5. Along with live wire and neutral wire, a third wire is also used in domestic electric wiring. What name is given to this third wire?

→ Earth wire is used along with live wire and neutral wire, a third wire is also used in domestic electric wiring.

6. List the colours of the three wires in the cable connected to the plug of an electric iron.

→ Red wire - Live wire
Black wire - Neutral wire
Green wire - Earth wire

7. What is the electric potential of the neutral wire in a mains supply cable ?

→ 0 volt is the electric potential of the neutral wire in a mains supply cable.

8. If fuses of 250 m A, 500 mA, 1 A, 5 A and 10 A were available, which one would be the most suitable for protecting an amplifier rated at 240 V, 180 W?

→ We know that,
I=p/v
So, by putting the values in the formula, we get
I= 180/240= 0.75A.
Fuse wire should must with stand only little more amount of current then 0.75A. so the required fuse is of 1A.

9. When does an electric short circuit occur?

→ When live wire and neutral wire come in contact with each other then in that case electric short circuit occur.

10. In which wire in an A.C. housing circuit is the switch introduced to operate the lights?

→ To operate the lights in an A.C housing circuit the switch is introduced with the live wire.

11. In household circuits, is a fuse wire connected in series or in parallel?

→ In housing circuit the fuse wire is connected in series.

12. Usually three insulated wires of different colours are used in an electrical appliance. Name the three colours.

→ Red, Black and Green are the three different colours of wire generally used in an electrical appliances.

13. What is the usual colour of the insulation of:
(a) live wire,
(b) neutral wire, and
(c) earth wire?

→ (a) The usual colour of the insulation of the live wire is red.
(b) The neutral wire is generally insulated with black colour.
(c) Green is the colour generally used for insolation of earth wire.

14. What is the main purpose of earthing an electrical appliance?

→ The main purpose of providing earthing in an electrical appliances is to avoid the risk of electric sock.

15. Give two reasons why different electrical appliances in a domestic circuit are connected in parallel.

→ The two reasons why different electrical appliances in a domestic circuit are connected in parallel are:-
1) Because of the parallel connection it is possible to use one application while the other is switched off.
2) Voltage remains same throughout in case of parallel connection.

16. How should the electric lamps in a building be connected so that the switching on or off in a room has no effect on other lamps in the same building?

→ The electric lamps in a building should be connected in parallel so that that switching off or on in a room has no effect on the other lamps in the same building.

17. Fill in the following blanks with suitable words:
(a) A fuse should always be placed in the .............wire of a mains circuit.
(b) The earth wire should be connected to the..............of an appliance.

→ (a) In the main circuit a fuse should always be connected with the live wire.
(b) The body of an appliances should always be connected with the earth wire.

18A. Of what substance is the fuse wire made? Why?

→ Tin-platted copper wire is used to manufacture the fuse. Because it has low melting point.

18B. Explain why, a copper wire cannot be used as a fuse wire.

→ The melting point of the copper wire is very high so it is not used as a fuse wire. That is because it will not allow the breakdown of the fuse wire which is not advisery.

19. What type of electric fuse is used in electrical appliances like car stereos? Explain with the help of a labelled diagram.

→ Cartridge fuses are used in electrical appliances like car stereos.
This type of fuse consist of consists of a glass tube T having a thin fuse wire sealed inside it. The glass tube has two metal caps at its two ends. The two ends of the fuse wire are connected to these metal caps. These are there for connecting the fuse in the circuit in a suitably made bracket.

20. Distinguish between the terms 'overloading' and 'short-circuiting ' as used in domestic circuits.

→ When live wire and the neutral wire came in contact with each other then short circuit happens.
On the other hand when too many electrical appliances of high power rating are switched on at the same time or are connected to a single socket, they draw extremely large amount of current. This is known as overloading.

21A. When does a fuse cut off current? How does it do it?

→ A fuse cuts off current when the current exceeds a safe value (due to short circuiting or overloading). When the current becomes large, it heats the fuse wire too much. Since the melting point of fuse wire is low, it melts and breaks the circuit. Thus, current in the circuits is cut off.

21B. What is the maximum number of 60 W bulbs that can be run from the mains supply of 220 volts if you do not want to overload a 5 A fuse?

→ Let us assume the number of bulbs be y.
Power of y bulbs, P=60y
V=220V, I=5A
We know that
P = VI
60y = 220 x 5
60y = 1100
y=18.33
So, number of bulbs required are 18.

22. Explain the importance of using in a household electric circuit
(i) fuse, and
(ii) earthing wire.

→ (i) fuse is used for the purpose of protection, and mainly used for avoiding the short circuit.
(ii) it is very important as it reduces the risk of electric sock, when live wire accidently touches the metal.

23A. An electric iron is rated at 230 V, 750 W. Calculate
(i) the maximum current, and
(ii) the number of units of electricity it would use in 30 minutes.

→ (a) (i) the max. current, I= PV
So, 3.260 A is the max current.
(ii) the number of units of electricity it would use in 30 minute is E= P*t
So, 0.75 KW*0.5h= 0.375 KWh.

23B. Which of the following fuse ratings would be suitable for this electric iron ?
1 A, 3 A, 5 A, 13 A.

→ The fuse rating suitable for this electric iron should be 5A.

24. What is the function of an earth wire? Why is it necessary to earth the metallic bodies of electrical appliances?

→ The function of an earth wire is, When the live wire of a faulty appliance comes in direct contact with its metallic case, which has been earthed, the large current passes directly to the earth without passing through the user's body. Thus, it is necessary to earth the metallic bodies of electrical appliances so as to avoid fatal electric shocks.

25A. What current is taken by a 3 kW electric geyser working on 240 V mains?

→ Given, P = 3kW = 3000W
V = 240V
P = V x I
I = P/V
= 3000/240 = 12.5 A
12.5A would be the required current.

25B. What size fuse should be used in the geyser circuit?

→ The size of the fuse in a geyser circuit is 13A.

26A. Why are fuses fitted in the fuse box of a domestic electricity supply?

→ It is there to protect the whole wiring in case of short circuit.

26B. What device could be used in place of the fuses?

→ The device used in place of the fuse is MCB.

27A. Draw a labelled diagram to show the domestic electric wiring from an electric pole to a room. Give the wiring for a bulb and a three-pin socket only. 27B. State two hazards associated with the use of electricity.

→ The two hazards associated with the use of electricity are:-
1) one may get electric sock if he touches the live wire.
2) Electrical fire can occur due to the short circuiting because of overloading.

27C. State the important precautions which should be observed in the use of electricity.

→ The important precautions which should be observed in the use of electricity are:-
1) Wires used should be good.
2) Proper earthing and fuse should must be used.
3) Electric appliances should be used only if they are dry.

27D. What will you do if you see a person coming in contact with a live wire?

→ We will switch off the main switch immediately so as to cut off the electricity supply if we see a person coming in contact with a live wire.

27E. Explain why, electric switches should not be operated with wet hands.

→ Electric switches should not be operated with wet hands because it may risk to electric sock.

Multiple Choice Questions (MCQs)-Pg-114

28. At the time of short circuit, the current in the circuit:
A. reduces substantially
B. does not change
C. increases heavily
D. varies continuously

→ At the time of short circuit, the current in the circuit increases heavily.

29. A 1.25 kW heater works on a 220 V mains supply. What current rating would a suitable fuse have ?
A. 2 A
B. 5 A
C. 10 A
D. 13 A

→ A 1.25 kW heater works on a 220 V mains supply. current rating suitable for the fuse would be 10A.

30. The maximum number of 40 W tube-lights connected in parallel which can safely be run from a 240 V supply with a 5 A fuse is :
A. 5
B. 15
C. 20
D. 30

→ The maximum number of 40 W tube-lights connected in parallel which can safely be run from a 240 V supply with a 5 A fuse is 30.

31. In normal use, a current of 3.5 A flows through a hair dryer. Choose a suitable fuse from the following:
A. 3 A
B. 5 A
C. 10 A
D. 30 A

→ In normal use, a current of 3.5 A flows through a hair dryer. The fuse required should be of 5A.

32. Which one of the following statements is not true?
A. In a house circuit, lamps are used in parallel.
B. Switches, fuses and circuit breakers should be placed in the neutral wire
C. An electric iron has its earth wire connected to the metal case to prevent the user receiving a shock
D. When connecting a three-core cable to a 13 A three-pin plug, the red wire goes to the live pin.

→ Switches, fuses and circuit breakers should be placed in the neutral wire is not true.

33. A car headlamp of 48 W works on the car battery of 12 V. The correct fuse for the circuit of this car headlamp will be:
A. 5 A
B. 10 A
C. 3 A
D. 13 A

→ A car headlamp of 48 W works on the car battery of 12 V. The correct fuse for the circuit of this car headlamp will be 5A.

34. A 3-pin mains plug is fitted to the cable for a 1 kW electric kettle to be used on a 250 V a.c. supply. Which of the following statement is not correct?
A. The fuse should be fitted in the live wire
B. A 13 A fuse is the most appropriate value to use
C. The neutral wire is coloured black
D. The green wire should be connected to the earth pin.

→ A 13 A fuse is the most appropriate value to use when A 3-pin mains plug is fitted to the cable for a 1 kW electric kettle to be used on a 250 V a.c. supply.

35. A TV set consumes an electric power of 230 watts and runs on 230 volts mains supply. The correct fuse for this TV set is :
A. 5 A
B. 3 A
C. 1 A
D. 2 A

→ The correct fuse for the TV set is of 2A when consumes an electric power of 230 watts and runs on 230 volts mains supply.

36. Circuit Breaker Device which can be used in place of fuse in domestic electric wiring is called:
A. CBD
B. DCB
C. MCD
D. MCB

→ Circuit Breaker Device which can be used in place of fuse in domestic electric wiring is called MCB.

37. An MCB which cuts off the electricity supply in case of short-circuiting or overloading works on the:
A. chemical effect of current
B. heating effect of current
C. magnetic effect of current
D. electroplating effect of current

→ An MCB which cuts off the electricity supply in case of short-circuiting or overloading works on the magnetic effect of current.

Questions Based on High Order Thinking Skills (HOTS)-Pg-115

38. An air-conditioner of 3.2 kW power rating is connected to a domestic electric circuit having a current rating of 10 A. The voltage of power supply is 220 V. What will happen when this air-conditioner is switched on? Explain your answer.

→ Given: P=3.2 kW=3200 W, Fuse current rating=10 A, V=220 V
We have
P=VI
3200 = 220 x I
I=14.54 A

The required current is 14.54A and the rated current is 10A for the fuse, so the breakdown will take place.

39. Three appliances are connected in parallel to the same source which provides a voltage of 220 V. A fuse connected to the source will blow if the current from the source exceeds 10 A. If the three appliances are rated at 60 W, 500 W and 1200 W at 220 V, will the fuse blow?

→ Given, P1=60 W, P2=1200W, P3=500W
Fuse rating = 10A
V=220V
We have, P=VI
Total power=60+1200+500=1760W
Therefore, 1760=220xI
I=8A
No, the fuse is of desired specification so it it will work properly.

40. A vacuum cleaner draws a current of 2 A from the mains supply.
(a) What is the appropriate value of the fuse to be fitted in its circuit?
(b) What will happen if a 13 A fuse is fitted in its circuit?

→ (a) the appropriate value of the fuse to be fitted in the circuit is 3A.
(b) if a 13 A fuse is fitted in its circuit, short-circuiting or overloading occur which can damage the vacuum cleaner.

41. Which of the following circuits will still be dangerous even if the fuse blows off and electric iron stops working during a short circuit? → Circuit A is not dangerous after fuse blows because fuse is in live wire so it will cut the connection; Circuit B is dangerous even if fuse blows because the fuse is in neutral wire .

42. An electric kettle rated as 1200 W at 220 V and a toaster rated at 1000 W at 220 V are both connected in parallel to a source of 220 V. If the fuse connected to the source blows when the current exceeds 9.0 A, can both appliances be used at the same time? illustrate your answer with calculations.

→ Given, P1=1200W, P2=1000W
V=220V
Fuse rating=9A
We know, P=VI
Total current required,
I = P/V
= (P1+P2)/V
= (1200+1000)/220
= 10A
The fuse will get burnt if both the appliances are switched on together. So one should not use both the appliances at the same time.

43. What is the main difference in the wiring of an electric bulb and a socket for using an electric iron in a domestic electric circuit? What is the reason for this difference?

→ There is No earth connection for electric bulb but for the electric iron;
The reason for this difference is, earth connection given to socket for electric iron.

44A. Explain why, it is more dangerous to touch the live wire of a mains supply rather than the neutral wire.

→ It is more dangerous to touch the live wire of a mains supply rather than the neutral wire because Live wire at high potential of 220 V on the other hand Neutral wire is at ground potential of 0 V.

44B. Why is it safe for birds to sit on naked power lines fixed atop tall electric poles?

→ It is safe for birds to sit on naked power lines fixed atop tall electric poles because bird's body is not connected to the earth, so no current flows through bird's body into the earth.

45. A domestic lighting circuit has a fuse of 5 A. If the mains supply is at 230 V, calculate the maximum number of 36 W tube-lights that can be safely used in this circuit.

→ Let the maximum number of tube-lights be y.
Power of y tube-lights, P=36y
V=230V, I=5A
We know that
P = VI
36y = 230 x 5
36y = 1500
y=31.94
So, number of tube-lights required are 31.

1. What produces magnetism in the human body?

→ The magnetism produces in the human body is because of ionic current flowing in the human body.

2. Name one medical technique which is based on magnetism produced in human body. For what purpose is this technique used?

→ (MRI) Magnetic Resonance Imaging is the technique based on magnetism procedure in human body. This is used to get image of the internal parts of the body.

3. Name two human body organs where magnetism produced is significant.

→ Brain and Heart are two parts where magnetism is being used for the treatment .

4. What is the full form of MRI?

→ The full form of (MRI) is Magnetic Resonance Imaging.

5. Name of the technique by which doctors can produce pictures showing insides of the human body.