[5 Mark Question Answer] - Physics STD 10 Questions - Vidyadip

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16 questions · timed · auto-graded

Question 15 Marks

A fuse is always connected to the live wire of the circuit. Explain the reason.

Answer

The fuse wire is always connected in the live wire of the circuit because if the fuse is put in the neutral wire, then due to excessive flow of current when the fuse burns, current stops flowing in the circuit, but the appliance remains connected to the high potential point of the supply through the live wire. Now if a person touches the appliance, he may get a shock as the person will come in contact with the live wire through the appliance.

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Question 25 Marks

Describe with the aid of a diagram some form of a fuse which is used in the electric lighting circuit of a house. Give two reasons why a fuse must not be replaced by an ordinary copper wire.

Answer

The figure above shows the most common fuse arrangement in which the fuse wire is stretched between the two metallic terminals T1 and T2 in a porcelain holder. This holder fits into a porcelain socket having two metallic terminals to each of which the live wire of the circuit is connected.
A fuse must not be replaced with a copper wire because copper has very low resistivity and high melting point.

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Question 35 Marks

How is a fuse put in an electric circuit? State the purpose of using a fuse in a circuit.

Answer

The fuse wire is stretched between the two metallic terminals T1 and T2 in a porcelain holder (since porcelain is an insulator of electricity). This holder fits into a porcelain socket having two metallic terminals to which the live wires of the circuit are connected. The figure below is showing the fuse arrangement

A fuse is connected with each electrical appliance to safeguard it from the flow of excessive current through it.

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Question 45 Marks

State two circumstances when one may get an electric shock from an electrical gadget. What preventive measure must be provided with the gadget to avoid it?

Answer

One may get an electric shock from an electrical gadget in the following two cases:
(i) If the fuse is put in the neutral wire instead of live wire and due to fault, if an excessive current flows in the circuit, the fuse burns, current stops flowing in the circuit but the appliance remains connected to the high potential point of the supply through the live wire. In this situation, if a person touches the faulty appliance, he may get an electric shock as the person will come in contact with the live wire through the appliance.
Preventive measure: The fuse must always be connected in the live wire.
(ii) When the live wire of a faulty appliance comes in direct contact with its metallic case due to break of insulation after constant use (or otherwise), the appliance acquires the high potential of the live wire. A person touching it will get a shock because current flows through his body to earth.
Preventive measure: Proper 'earthing' of the electric appliance should be done.

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Question 55 Marks

To which wire is the metallic case of an electric appliance connected? give the reason?

Answer

If the live wire of a faulty appliance comes in to direct contact with the metallic case due to some reason then the appliance acquires the high potential of live wire. This may results in shock if any person touches the body of appliance. But if the appliance is earthed then as soon as the live wire comes in to contact with the metallic case, high current flows through the case to the earth. The fuse connected to the appliance will also blows off, so the appliance get disconnected.

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Question 65 Marks

What do you mean by the term local earthing? Explain how it is done.

Answer

Local earthing is made near kWh meter. In this process a 2 - 3 metre deep hole is dug in the ground. A copper rod placed inside a hollow insulating pipe, is put in the hole. A thick copper plate of dimensions 50 cm × 50 cm is welded to the lower end of the copper rod and it is buried in the ground. The plate is surrounded by a mixture of charcoal and salt to make a good earth connection.
To keep the ground damp, water is poured through the pipe from time to time. This forms a conducting layer between the plate and the ground. The upper end of the copper rod is joined to the earth connection at the kWh meter.

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Question 75 Marks

The diagram in Fig. 9.27 shows a three pin plug. Label the three pins.
(a) why if the top pin thicker and longer than the other two?
(b) why are the pins splitted at the ends?

Answer

The three pins in the plug are labelled as

Here E signifies the earth pin,
L is for live wire, and
N is for neutral wire.
(a) The earth pin is made long so that the earth connection is made first. This ensures the safety of the user because if the appliance is defective, the fuse will blow off. The earth pin is thicker so that even by mistake it cannot be inserted into the hole for the live or neutral connection of the socket.
(b) The pins are splitted at the end to provide spring action so that they fit in the socket holes tightly.

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Question 85 Marks

Draw a circuit diagram using the dual control switches to light a staircase electric light and explain its working.

Answer

Dual control switches are the double pole type switches which are generally used at the top and bottom of a staircase, or at the opposite ends of a long corridor, etc. With such switches, the appliance (say, a bulb) can be switched on or off from, two different places.

(b) Bulb on through switch $S_1$

(c) Bulb on through switch $S_2$

The working and circuits of a dual control switch are illustrated in Fig. a,b,c. Let a switch $S _1$ be fitted at the top of the staircase. Fig. (a) shows the off position of the bulb.
The bulb can now be switched on independently by either the switch $S _1$ or the switch $S _2$ If the switch $S _1$ is operated, the connection 'ab' is changed to 'bc', which completes the circuit and the bulb lights up [Fig. (b)]. Similarly, on operating the switch $S _2$, the connection 'bc' changes to 'ba', which again completes the circuit [Fig. (c)]. Similarly, if the bulb is in on position as shown in Fig. (b), one can switch off the bulb by changing the connections 'ab' to 'bc' either by the switch $S _1$ or the switch $S _2$.
In a staircase, while going up a person puts on the light by operating the switch $S _1$ so that the connection 'ab' changes to 'bc' and makes the current flow in the circuit. On reaching at the top of operates the switch $S _2$ to put off the light so that the connection 'cb' changes to 'ba' and the flow of current stops.
The same system is operative when a person puts on light by operating the switch $S _2$ to change the connection 'cb' to 'ba' and switch off the light by operating the switch $S _1$ to change the connection 'ab' to 'bc'.

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Question 95 Marks

It is dangerous to connect the switch in the neutral wire. Explain your answer.

Answer

In case of excessive current, it is dangerous to connect the switch in the neutral wire.

Even if the fuse blows off due to excessive current and the current in the circuit would no longer be conducted, the appliance will still remain connected to the live wire of a very high potential.

In such a case, if a person touches the body of that appliance, he/she may suffer a fatal electric shock.

That is why it is highly dangerous to connect the switch with the neutral wire.

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Question 105 Marks

What is the purpose of a switch in a circuit? Why is the switch put in the live wire? What
precaution do you take while handling a switch?

Answer

A switch is an on-off device for current in a circuit (or in an appliance). The switch should
always be connected in the live wire so that the appliance could be connected to the high
potential point through the live wire. In this position the circuit is complete as the neutral wire provides the return path for the current. When the appliance does not work i.e., in off position of the switch, the circuit is incomplete and no current reaches the appliance.

On the other hand, if switch is connected in the neutral wire, then in 'off' position, no current passes through the bulb. But the appliance remains connected to the high potential terminal through the live wire.

Thus, if the switch is connected in the neutral wire, it can be quite deceptive and even dangerous for the user.
Precaution while handling a switch: A switch should not be touched with wet hands.

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Question 115 Marks

(a) Name the three connecting wires used in a household circuit
(b) Which of the two wires mentioned in part (a) are at the same potential?
(c) In which of the wire stated in part (a) the switch is connected?

Answer

(a) The three connecting wires used in a household circuit are:
(i) Live (or phase) wire (L),
(ii) Neutral wire (N), and
(iii) Earth wire (E).
(b) Among them neutral and earth wires are at the same potential.
(c) The switch is connected in the live wire

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Question 125 Marks

Explain with the aid of a simple diagram, the transmission of electric power from the generating station to your house.

Answer

At a power generating station, the electric power is generated at 11 kV. From here, the alternating voltage is transmitted to the grid sub-station and stepped up to 132 kV using a step-up transformer. It is then transmitted to the main sub-station where the voltage is stepped down to 33 kV using a step-down transformer and is then transmitted to the intermediate sub-station. At the intermediate sub-station, the voltage is stepped down to 11 kV using a step-down transformer and is transmitted to the city sub-station, where the voltage is further stepped down to 220 V and is supplied to our houses.

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Question 135 Marks

The voltage of power generated at the generating stations is first stepped up before its transmission. Give reason.

Answer

Power generated at generating stations is usually about 11kV, which is very high.

This power from the generating stations is to be transmitted across far away distances.

While transmitting the 11kV power, a lot of energy is lost in the form of heat in the transmission line wires.

Therefore, the voltage of power generated at the stations is raised or stepped up from 11kV to 132kV using the step-up transformer.

As direct current cannot be raised, this process is applicable only for alternating current.

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Question 145 Marks

Two sets A and B of four bulbs each are glowing in two separate rooms. When one of the bulbs in set A is fused, the other three bulbs also cease to glow. But in set B, when one bulb fuses the other bulbs continue to glow. Explain the difference.

Answer

In set A, the bulbs are connected in series. Thus, when the fuse of one bulb blows off, the circuit gets broken and current does not flow through the other bulbs also.
In set B, the bulbs are connected in parallel. Thus, each bulb gets connected to its voltage rating (= 220 V) and even when the fuse of one bulb blows off, others remain unaffected and continue to glow.

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Question 155 Marks

In following figure shows three bulbs A, B and C each of rating 100 W, 220 V connected to the mains of 220 V. Answer the following:

(a) How is the bulb A connected with the mains? At what voltage does it glow?(b) How are the bulbs B and C connected with the mains? At what the bulb A connected with the mains?(c) How is the glow of bulbs A and C affected if bulb B gets fused?(d) How is the glow of bulbs B and C affected if bulb A gets fused?

Answer

(a) Bulb A is connected in a parallel connection with the mains.

It will glow when the voltage applied across the bulb is 220 V.

(b) Bulbs B and C are connected in series with the mains. Because of this series connection with the mains, the voltage at which they glow will be divided by two from the main's supply voltage. So, bulb B will glow at 110V.

(c) If bulb B gets fused, bulb C which was connected in series with it will not glow. This will not affect the glow of bulb A, because it is connected parallel with the mains.

(d) If bulb A gets fused, the glow of bulbs B and C will not be affected.

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Question 165 Marks

Draw a circuit diagram to expain the ring system of house wiring. State two advantage of it.

Answer

Advantages of ring system over tree system
(i) In a ring system the wiring is cheaper than tree system.
(ii) In ring system the sockets and plugs of same size can be used while in a tree system sockets and plugs are of different size.
(iii) In ring system, each appliance has a separate fuse due to which if there is a fault and the fuse of one appliance burns it does not affect other appliances; while in a tree system when fuse in one distribution line blows, it disconnects all the appliances connected to that distribution circuit.

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[5 Mark Question Answer] - Physics STD 10 Questions - Vidyadip