# Class-10 Goyal Electric Energy, Power and Household Circuits ICSE Physics Solutions Ch-9

Class-10 **Goyal Brothers Electric Energy, Power and Household Circuits **ICSE Physics Solutions Ch-9 . We Provide Step by Step Answer of Exercise, MCQs, Numerical Problem Questions of Exercise-1 & 2** Goyal Brothers Electric Energy, Power and Household Circuits ICSE Class-10**** **. Visit official Website **CISCE ** for detail information about ICSE Board Class-10 Physics.

## Electric Energy, Power and Household Circuits Class-10 Goyal Brothers ICSE Physics Solutions Ch-9

-: Select Topics :-

**Exe-1 Class-10**

Electric Energy, Power and Household Circuits** Goyal Brothers ICSE Physics Solutions Ch-9**

**Page-150**

**Question 1.**

**(a)** What do you understand by the term electric work ?

**Answer:**

**Electric work :** “Electric work is said to be done when an electric charge flows through a conductor, at some potential difference.”

**(b)** State and define SI unit of electric work.

**Answer:**

S.I. unit of electric work → Joule (J)

1J = 1 volt × 1 coulomb

**1 Joule :** “Is the amount of work done when a charge of one coulomb flows through a conductor at a pot. diff. of 1 volt.”

**(c)** Name two bigger units of electric work. How are they related to SI unit ?

**Answer:**

**Two bigger units of electric work :**

- Kilo – Joule (kJ) = 10
^{3}J - Mega-joule (Mj) = 10
^{6}J

**Question 2.**

**Derive an expression for electric work connecting :**

**(a)** Current, resistance and time

**(b)** Current, potential difference and time.

**(c)** Potential difference, resistance and time.

**Answer:
**

**Question 3.**

State three factors which determine the quantity of heat produced in a conductor.

**Answer:**

Three factors which determine heat produced in a conductor :

Heat produced = Energy Work done

W=H=I^{2}Rt

∴ Three factors are I — current

R — Resistance of conductor

t — time for which current flows.

**Question 4.**

**(a)** What do you understand by the term electric power ?

**(b)** State SI unit of electric power and define it

**(c)** Name two bigger units of electric power and their relation with SI unit.

**Answer:
**

**Question 5.**

**Derive an expression for electric power connecting :**

**(a)** Current and resistance.

**(b)** Current and potential difference.

**(c)** Potential difference and resistance.

**Answer:
**

**Question 6.**

**(a)** What do you understand by term electric energy ?

**(b)** Name and define the smallest commercial unit of electric energy.

**(c)** Name and define the standard commercial unit of electric energy.

**Answer:**

**(a) Electric energy :** E = P × t = VIt

“Electric energy is the product of power and time.” i.e. electric energy consumed by an electrical appliance is produced of ‘power rating’ and ‘time’ for which it is used.

**(b)** Unit of electric energy → Joule (J)

S.I. unit of electric work → Joule (J)

1J = 1 volt × 1 coulomb

**1 Joule :** “Is the amount of work done when a charge of one coulomb flows through a conductor at a pot. diff. of 1 volt.”

**(c) Standard Commercial unit of Electric Energy :** Kilo-watt-Hour 1 kwH : “Is the amount of electrical energy consumed when an electrical appliance having a power rating of 1 kilowatt is used for 1 hour.”

**Question 7.**

**With respect to electricity, define :**

- watt hour
- watt
- kilowatt
- kilowatt hour. Amongst the above units, which are the units of : (i) electric energy (ii) electric power.

**Answer:
**

**Question 8.**

How many joules of energy is equal to one kilowatt hour?

**Answer:
**

**Question 9.**

Distinguish between kilo-watt and kilowatt hour.

**Answer:
**

**Question 10.**

How many kilowatt is equal to one hour power ?

**Answer:
**

** ****Multiple Choice Questions-1**

### Electric Energy, Power and Household Circuits **Class-10 Goyal Brothers** ICSE Physics Solutions

**1. A bulb has a resistance of 20 Ω and the p.d across its terminals is V. If the bulb is usedfor t seconds then energy consumed by the bulb is :
**

**Answer:**

**2. A current Iflows through a resistance R for the time ‘t’, the electric energy consumed by the resistance is :
**

**Answer:**

**3. The unit for electric work in SI system :**

(a) Joule

(b) watt

(c) watt second

(d) watt hour

**Answer:**

(a) Joule

**4. An electric appliance has a rating of 1000 W – 200 V. The resistance of the element of electric appliance is :**

(a) 200 Ω

(b) 400 Ω

(c) 40 Ω

(d) 4000 Ω

**Answer:**

(c) 40 Ω

**5. Kilowatt hour is commercial unit of :**

(a) power

(b) electric energy

(c) heat energy

(d) mechanical energy

**Answer:**

(b) electric energy

**6. Kilowatt hour and kilowatt are :**

(a) SI units of power and electric energy

(b) commercial units of power and electric energy

(c) SI units of-electric energy and power

(d) commercial units of electric energy and power

**Answer:**

(d) commercial units of electric energy and power

**Numerical Problem ****on Electric Energy**

**on Electric Energy**

Electric Energy, Power and Household Circuits **Class-10 Goyal Brothers** ICSE Physics Solutions

Page-152

**Practice Problems 1**

**Question 1.**

Calculate the energy released by a heater, which draws a current of 5A at 220 V for 1 min.

**Answer:
**

**Question 2.**

An electric device consumes 8640 J of energy in 30 min. while operating at 24 V. Calculate the current drawn by the device.

**Answer:
**

**Practice Problems 2**

**Question 1.**

An ekctric kettle draws a current of4A for 2.5 min. if the resistance of its element is 100 Ω , calculate the electric energy drawn by kettle in kilojoules.

**Answer:
**

**Question 2.**

A soldering iron draws an energy of 43200 J in 4 min, when the current flowing through its element is 6 A, calculate the resistance of its heating element.

**Answer:
**

**Practice Problems 3**

**Question 1.**

Calculate the heat energy given out by the filament of an electric bulb in 20 s, when its resistance is 4 Ω and p.d. across its ends in 12 V.

**Answer:
**

**Question 2.**

An electric device gives out 5760 J of heat energy in 1 min, when current flows through it at a p.d. of 24 V. Find the resistance of the device.

**Answer:
**

**Practice Problems 4**

**Question 1.**

An electric heater draws a current of 3.5 A at a p.d. of 250 V. Calculate the power of 4 such heaters.

**Answer:
**

**Question 2.**

An electric bulb is rated 500 W – 200 V. Calculate the magnitude of current.

**Answer:
**

**Question 3.**

An electric heater of power 1000 W, draws a current of 5.0 A. Calculate the line voltage.

**Answer:
**

**Practice Problems 5**

**Question 1.**

An electric heater has a resistance of 40 Ω and draws a current of 4 A. Calculate :

- its power
- p.d. at its ends

**Answer:
**

**Question 2.**

An electric heater of power 900 W, has a resistance of 36 Ω Calculate the magnitude of current and the p.d. at its ends.

**Answer:
**

**Practice Problems 6**

**Question 1.**

An electric motor of power 1000 W, operates at 250 V. Calculate the inductive resistance of motor and current flowing through it.

**Answer:
**

**Question 2.**

An electric device operates at 24 V and has a resistance of 8 Ω Calculate the power of the device and current flowing through it

**Answer:
**

**Practice Problems 7**

**Question 1.**

An electric bulb is rated 200 W – 200 V. It is immersed in 200 g of oil (SHC 0.8 Jg^{-10} C^{-1}) at 10°C. The bulb is switched on for 2 minutes. If all the electric energy is absorbed in the form of heat energy by the oil, calculate :

**(a)** Resistance of the filament of the bulb.

**(b)** Current flowing through the bulb.

**(c)** Final temperature of the oil.

**Answer:
**

**Question 2.**

An electric kettle is rated 1000 W – 250 V. It is used to bring water at 20°C to its boiling point. If the kettle is used for 11 minutes and 12 seconds, **calculate :**

**(a)** Resistance of the element of the kettle.

**(b)** Current flowing through the element.

**(c)** Mass of water in the kettle [SHC of water = 4.2 Jg^{-10} C^{-1}]

**Answer:
**

**Practice Problems 8**

**Question 1.**

Calculate the resistance of nichrome wire, which will bring 200 g of water at 20° C to its boiling points in 7 minutes, when current flowing through wire is 4A.

**Answer:
**

**Question 2.**

Calculate p.d. at the ends of a power source which, supplies current to a 4 ohm resistance wire for 20 minutes and raises temperature of 400 g of water through 20 .

**Answer:
**

**Question 3. Class-10 Goyal Electric Energy**

Calculate the current flowing through an electric drill, connected to 200 V supply, if it drills a hole in a metal plate of mass 500 g, such that its temperature rises from

10 to 60 in 5 minutes, assuming all the work done is converted into heat energy.

[S.H.C. of metal 0.6 Jg^{-1} ^{-1}]
**Answer:
**

**Practice Problems 9**

**Question 1.**

Circuit diagram shows four dry cells of e.m.f. 1.5 V and internal resistance 0.25 Ω connected to an external circuit A 3 Ω wire is immersed in 20 g of water at 20°C. The current switched on for 6 minutes and 36 seconds. Calculate :

**(a)** Reading shown by the ammeter

**(b)** Current in 1.5 Ω wire

**(c)** Final temperature of water

**Answer:
**

**Question 2.**

A battery of 12 V and negligible internal resistance is connected to an external circuit consisting of three resistors of 6 Ω, 3 Ω and 2 Ω in parallel, which further connected to a resistance of 3 Ω in series to the battery. The 3 Ω resistance is immersed in 50 g oil of sp. heat capacity 0.8 Jg-10 C^{-1}, when the temperature of the oil rises by 54 ^{0}C.

**(a)** Draw the labelled circuit diagram.

**(b)** Calculate the value of current in the tnain circuit.

**(c)** Calculate the current following in 2 Ω resistance in parallel.

**(d)** Calculate the time for which current is switched on.

**Answer:
**

**Practice Problems 10**

**Question 1.**

An electric kettle rated 250 V can bring a certain amount of water to its boiling point in 8 min. If it is connected to 200 V mains, calculate the time in which water comes to its boiling point.

**Answer:
**

**Question 2.**

An immersion heating rod is rated 220 V and can bring certain amount of water to its boiling point in 15 min. When this immersion rod is actually connected to an electric circuit, it brings the water to boil in 18.15 min. Calculate the line voltage.

**Answer:
**

**Practice Problems 11**

**Question 1.**

An electric oven is marked 1000 W – 200 V. Calculate :

**(a)** Resistance of its element

**(b)** Energy consumed by the oven in 1/2 hour in joules.

**(c)** Time, in which ii will consume 15 kWh of energy.

**Answer:
**

**Question 2.**

An electric motor is rated 2 HP – 250 V. Calculate :

**(a)** Current flowing through it

**(b)** Energy consumed by it in one second

**(c)** Time in which it will consume 90 kWh of energy. [1 HP = 750 W]

**Answer:
**

**Practice Problems 12**

**Question 1.**

A geyser is rated 2000 W and operates 2 hours a day on 200 V mains. Calculate the monthly bill for running the geyser when energy costs ₹ 1.90 per kWh.

**Answer:
**

**Question 2.**

An electric oven of resistance 20 Ω draws a current of 10 A. It works 3 hours daily. Calculate the weekly bill when enregy costs ₹ 1.50 per kWh.

**Answer:
**

**Question 3. Class-10 Goyal Electric Energy**

An electric bulb draws a current of 0.8 A and works on 250 V on an average 8 hrs a day. If energy costs ₹ 1.50 per board of trade unit, calculate the monthly bill

**Answer:
**

**Practice Problems 13**

**Question 1.**

4 tube lights of 40 W each and 2 fans of 100 W each are connected to 200 V mains and operate on an average 8 hours a day. If energy costs ₹ 1.50 kWh, calculate

**(a)** monthly bill

**(b)** minimum fuse rating.

**Answer:
**

**Question 2.**

An electric motor of 2 H.P. and two coolers of 500 W each operate on 250 V mains for 4 hours a day. If the energy costs ₹ 1.80 per kWh, calculate

**(a)** weekly bill

**(b)** minimum fuse rating. [Take 1 HP = 750 W]

**Answer:
**

**Practice Problems 14**

**Question 1.**

A boys hostel has following appliances when energy is supplied at 200 V and costs ₹ 5.25 per kWh.

**(a)** 40 bulbs of 100 W each, working 8 hours a day.

**(b)** 20 fans each drawing a current 9.8 A and working 15 hours a day.

**(c)** Two T.V. sets, each offering a resistance of 200 Ω and working 4 hours a day.

**(d)** Two electric motors of 1.5 H.P. each and working 4 hours a day

- Calculate the monthly bill
- Amongst the fuse of 48 A and 50 A which one you will use and why ?

**Answer:
**

**Question 2. Class-10 Goyal Electric Energy**

An establishment receives electric energy at a rate of ₹ 4.50 per kWh at a p.d. of 240 V. It uses following appliances.

**(a)** 20 tube lights of 40 W each working 10 h a day.

**(b)** Two stero systems, each drawing a current of 2A and working 4h a day.

**(c)** Four ovens, each of resistance 24 Q working 6 h a day.

**(d)** Two cooling machines of 4 H.P. each working 15 hours a day.

- calculate monthly bill
- minimum fuse rating of circuit

**Answer:
**

**Exe-2 Class-10**

### Electric Energy, Power and Household Circuits** Goyal Brothers ICSE Physics Solutions Ch-9**

**Page-165,166**

**Question 1.**

**(a)** What do you understand by the term electric fuse ?

**Answer:**

**Electric fuse :** “Is a safety device which is used to limit the current in an electric circuit. The use of a fuse safe guards the circuit and the appliances connected in that circuit from being damaged.”

**(b)** Name a material from which an electric fuse is made.

**Answer:**

Material used for fuse is ‘Alloy of lead and Tin’ having low melting point and high resistance.”

**(c)** State two properties of a material which makes it suitable for an electric fuse.

**Answer:**

**Two properties of material are :**

- Low melting point
- High resistance.

**(d)** Draw a diagram of a fuse wire, connected in a fuse socket.

**Answer:
**

**Question 2.**

**(a)** Why is a fuse wire always placed in a live wire ?

**Answer:**

So that ‘The fuse may melt first, before current reaches the appliance”.

**(b)** How does fuse wire protect an electric circuit ?

**Answer:**

When current in the circuit exceeds the specified value (due to any reason such as high voltage, short circuiting etc.) the fuse wire gets heated up to the extent that it melts. As a result a gap is produced and the circuit beaks. The current does not flow through the live wire and appliance is saved.

**(c)** Two fuse wires of the same length are rated 15A and 5A. Which of the two is thicker and why ?

**Answer:**

5A wire is thicker as resistance is α 1/a Thicker the wire less is resistance and electrons can run freely with less collisions.

**(d)** Why is it dangerous to replace a fuse wire with a copper wire?

**Answer:**

“Copper has low resistivity and high melting point and does not serve the purpose of fuse.”

**Question 3.**

**(a)** What do you understand by the term earthing ?

**Answer:**

**Earthing : or Grounding :** “Bringing the appliance to zero potential”.

“Earthing means to connect the metal case of electrical appliance to the earth (at zero potential) by means of a metal wire is called “Earth wire”.

**(b)** How does earthing protect a user from receiving an electric shock?

**Answer:**

When we connect the earth wire to the metal case of the electrical appliance by using three pinplug.

The metal casing of the appliance will now always remain at zero potential of the earth, this will avoid the risk of shock if we touch the metal body as the current passes directly to earth through the earth wire.

**(c)** How is a household circuit earthed ?

**Answer:**

The neutral and earth wires on supply end (power station) are connected potential together, so that both of them are at zone potential and inside the house live and neutral wires are connected to the input terminals of kWh meter, where as earth wire is connected to the body of kWh meter. The live wire coming out from the out put terminals of the kWh meter has another fuse in it, which is commonly called main fuse. The neutral wire and earthwire is common to all circuits.

**(d)** Explain how the fuse melts when a short circuit appliance gets earthed.

**Answer:**

When an earthed appliance gets short circuited, then current from its metal body flows into the earth. Since earth does not offer any resistance, therefore magnitude of the current in the circuit of a short-circuited appliance suddenly rises to a very high value.

This rise in magnitude of current in turn overloads the circuit, and hence. The fuse in that circuit melts.

**Question 4. Class-10 Goyal Electric Energy**

**(a)** What is the function of a switch in an electric circuit?

**Answer:**

**Function of a switch :**

Function of a switch is to connect or disconnect an electric appliance in the electric circuit.

**(b)** Why is switched placed in a live wire ?

**Answer:**

Let the appliance (heater) when connected in a neutral wire, when the switch is in the off position and even if no current is flowing through the heater and it is not operating, how ever the heater is in contact with live wire and heating element is at the same potential as the live wire. Thus if we touch the heating coil of the heater, current will flow through our body giving us a severe shock and may prove fatal, this proves that switch should always be placed in the live wire.

**(c)** what consequences will follow, if a switch is placed in the neutral wire ?

**Answer:**

Even if switch is in off position the appliance will be at the potential of live wire and current will flow through the appliance.

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