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Selina solutions Selina ICSE Concise Physics for Class 10 chapter 9 Electrical Power and Household Circuits

Chapters

Selina Selina ICSE Concise Physics Class 10

Selina ICSE Concise Physics for Class 10

Chapter 9 - Electrical Power and Household Circuits

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Write an expression for the electrical energy spent in flow of current through an electrical appliance in terms of current, resistance and time.

Write an expression for the electrical power spent in flow of current through a conductor in terms of
(a) Resistance and potential difference, (b) current and resistance.

Electrical power p is given by the expression P = (Q × V) ÷ time
(a) What do the symbols Q and V represent?

Electrical power p is given by the expression P = (Q × V) ÷ time

Express the power P in terms of current and resistance explaining the meaning of symbols used there in.

Name the S.I. unit of electrical energy. How is it related to Wh?

Name the S.I unit of electrical energy. How is it related to Wh?

State the S.I. unit of electrical power.

 State and define the household unit of electricity.

What is the voltage of the electricity that is generally supplied to a house?

Name the physical quality which is measured in
(i) Kw (ii) kWh

Define the term kilowatt-hour and state its value in S.I unit

Distinguish between kilowatt and kilowatt-hour.

 1Kwh =`( 1  "volt "xx 1 am pere xx.............)/1000`

1kWh = …….. J

What do you mean by power rating of an electrical appliance? How do you use it to calculate  the resistance of the appliance .

What do you mean by power rating of an electrical appliance? How do you use it to calculate the safe limit of current in it, while in use?

An electric bulb is rated ‘100 W, 250 V’. What information does this convey?

List the names of three electrical gadgets used in your house. Write their power, voltage ratingand approximate time for which each one is used in a day. Hence find the electrical energyconsumed by each in a day.

Two lamps, one rated 220 V, 50 W and the other rated 220 V, 100 W, are connected in serieswith mains of 220 V. Explain why does the 50 W lamp consume more power

Name the factors on which the heat produced in a wire depends when current is passed in it, and state how does it depend on the factors stated by you.

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When a current I flows through a resistance R for time t, the electrical energy spent is given by:
(a) IRt (b) I²Rt (c) `IR^2t` (d) `I^2R ⁄t`

An electrical appliance has a rating 100 W, 120 V. the resistance of element of appliance when in use is:
(a) 1.2Ω (b) 144 Ω (c) 120 Ω (d) 100 Ω

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A current of 2 A is passed through a coil of resistance 75Ω for 2 minutes. (a) How much heat energy is produced? (b) How much charge is passed through the resistance?

Calculate the current through a 60 W lamp rated for 250 V. If the line voltage falls to 200 V, how is the power consumed by the bulb affected?

An electric bulb is rated ‘100 W, 250 V’. How much current will the bulb draw if connected to a 250 V supply?

An electric bulb is rated at 220 V, 100 W. (a) what is its resistance? (b) what safe current can be passed through it?

A bulb of 40 W is used for 12.5 h each day for 30 days. Calculate the electrical energy consumed.

An electric iron is rated at 750 W, 230 V. Calculate the electrical energy consumed by the iron in 16 hours .

An electrical appliance having a resistance of 200Ω is operated at 200 V. Calculate the energy consumed by the appliance in 5 minutes (i) in joules (ii) in kWh.

A bulb marked 12 V, 24 W operated on a 12 volt battery for 20 minutes. Calculate:
(i) the current flowing through it, and
(ii) the energy consumed

A current of 0.2 A flows through a wire whose ends are at a potential difference of 15 V.
calculate:
(i) the resistance of the wire and
(ii) the heat energy produced in 1 minute.

What is the resistance, under normal working conditions of a 240 V electric lamp rated at 60 W? If two such lamps are connected in series across a 240 V mains supply, explain why each one appears less bright.

Two bulbs are rated 60 W, 220 V and 60 W, 110 V respectively. Calculate the ratio of their
resistances

An electric bulb is rated 250 W, 230 V calculate:
(i) the energy consumed in one hour
(ii) the time in which the bulb will consume 1.0 kWh energy when connected to 230 V mains.

Three heaters each rated 250 W, 100 V are connected in parallel to a 100 V supply. Calculate:
(i) the total current taken from the supply
(ii) the resistance of each heater and
(iii) the energy supplied in kWh to the three heaters in 5 hours.

A bulb is connected to a battery of p.d 4 V and internal resistance 2.5 Ω A steady current of 0.5
A flows through the circuit calculate:
(i) the total energy supplied by the battery in 10 minutes
(ii) the resistance of the bub and
(iii) the energy dissipated in the bulb in 10 minutes.

Two resistors A and B of resistance 4 Ω and 6 Ω respectively are connected in parallel. The combination is connected across a 6 volt battery of negligible resistance. Calculate: (i) the power supplied by the battery, (ii) the power dissipated in each resistor.

A battery of e.m.f 15 V and internal resistance 2 Ω is connected to two resistors of resistance 4 ohm and 6 ohm joined in series. Find the electrical energy spent per minute in 6 ohm resistor.

Water in an electric kettle connected to a 220 V supply took 5 minutes to reach its boiling point. How long would it have taken if the supply voltage had fallen to 200 V?

An electric toaster draws 8 A current in a 220 V circuit. It is used for 2 h. Find the cost of
operating the toaster if the cost of electrical energy is Rs. 4.50 per kWh.

An electric kettle is rated 2.5 kW, 250 V. Find the cost of running the kettle for two hours at Rs. 5.40 per unit.

A geyser is rated 1500 W, 250 V. This geyer is connected to 250 V mains. Calculate:
(i) the current drawn
(ii) the energy consumed in 50 hours, and
(iii) the cost of energy consumed at Rs. 4.20 per kWh

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At what voltage and frequency is the electric power generated at the power generating station?

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

At what voltage is the electric power from the generating station transmitted? Give reason to your answer.

At what voltage and frequency is the a.c. supplied to our houses?

Name the device used to (a) increase the voltage at the generating station (b) decrease the voltage at the substation for its supply.

(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?

What is the pole fuse? Write down its current rating.

State the function of each of the following in a house circuiting?
(a) kWh meter (b) main fuse, and (c) main switch

In what unit does the electric meter in a house measure the electrical energy consumed? What is its value in S.I unit?

Where is the main fuse in a house circuit connected?

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

Draw a labelled diagram with necessary switch, regulator, etc. to connect a bulb and a fan with the mains. In what arrangement are they connected to the mains : series or parallel?

How should the electric lamps be connected with the mains so that the switching on or off a lamp has no effect on other lamps?

Fig 9.15 shows two ways (a) and (b) of connecting the three lamps A, B and C to a.c. supply of 220 V. Name the two arrangements. Which of them would you prefer in a household circuit? Give reason for your answer.

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.

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The main fuse is connected in:
(a) live wire
(b) neutral wire
(c) both the live and earth wires
(d) both earth and the neutral wire

The electrical appliances in a house are connected in:
(a) series
(b) parallel
(c) either in series or parallel
(d) both in series and parallel

The electric meter in a house records:
(a) charge

(b) current

(c) energy

(d) power

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What is a fuse? Name the material of fuse. State on characteristic of material used for fuse.

Name the device used to protect the electric circuits from over loading and short circuit. On what effect of current does it work?

Complete the following sentence:
(A fuse is a short piece of wire of material of high …………and low ………..

Complete the following sentence:

A fuse wire is made of an alloy of ………. and …..If the current in a circuit rises too high, the fuse wire ……….

Complete the following sentence:

A fuse is connected in …… with the ………..wire.

Why is the fuse wire fitted in a porcelain casing?

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

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.

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

Two fuse wire of same length are rated 5 A and 20 A. Which of the two is thicker and why?

Explain the meaning of the statement ‘the current rating of a fuse is 5 A’.

‘A fuse is rated 8 A’. can it be used with an electrical appliance of rating 5kW, 200V?

An electric kettle is rated 3 kW, 250 V. give reason whether this kettle can be used in a circuit
which contains a 13 A fuse.

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?

A switch is not touched with wet hands while putting it on or off. Give a reason for your answer.

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

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?

What purpose is served by the terminals of a three way pin plug? Draw a diagram and name the pins

E: for earth pin
N: for neutral wire pin
L: for live wire pin.

The diagram in Fig. 9.28 shows a three pin socket marked as 1, 2 and 3.
(a) Identify and write live (L) neutral (N) and earth (E) against the correct number
(b) To which part of the appliance is the terminal 1 connected?
(c) To which wire joined to 2 or 3, is the fuse connected and why?

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

The metal case of an electric appliance is earthed explain the reason.

(a) the earthing of an electric appliance is useful only if the fuse is in the love wire. Explain the reason.
(b) Name the part of the appliance which is earthed.

For earthing an electrical appliance, one has to remove the paint from the metal body of the appliance where the electrical contact is made. Explain the reason.

What is the colour code for the insulation on the (a) live (b) neutral and (c) earth wire?

A power circuit uses a cable having three different wires.
(a) Name the three wires of the cable.
(b) to which of the two wires should the heating element of an electric geyser be connected?
(c) To which wire should the metal case of the geyser be connected?
(d) to which wire should the switch and fuse be connected?

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?

Why is it necessary to have an earth wire installed in a power circuit, but not in a lighting circuit?

Give two characteristic of a high tension wire.

Which of the cables, one rated 5 A and the other 15 A will be of thicker wire? Give a reason for your answer.

The diagram in Fig. 9.29 shows three lamps and three switches 1, 2 and 3
(a) Name the switch / switches to be closed so as to light all the three lamps.
(b) How are the lamps connected: in series or in parallel?

Fig 9.30 below shows two bulbs with switches and fuse connected to mains through a socket.
(a) label each component
(b) Name and state the colour of insulation of each wire 1, 2 and 3
(c) How are the two bulbs joined : in series or in parallel?

Selina Selina ICSE Concise Physics Class 10

Selina ICSE Concise Physics for Class 10
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