MG SCHOOL EDUCATION: Cls 10 Sci Chp 12 prv yr qn ans

Class 10 Science

Previous Years Appeared Questions and Answer

Chapter 12 Electricity

Multiple Choice Questions

1. The SI unit of resistivity is ( June-22)

(A) ohm (B) volt

Ans. : (D) ohm-metre

2. The correct formula that shows the relationship between potential difference, electric current and resistance in an electric circuit is (April - 2022)

(A) I = R/V (B) I=VR

Ans: (D) R=V/I

3. A piece of metallic wire of resistance R is cut into 3 equal parts. These parts are then connected in parallel. If the total resistance of this combination is Rl, then the value of R : Rl is (June - 2019)

(A) 1 : 3 (B) 9 : 1

Ans: (B) 9 : 1

4. The resistance of a conductor is 27 Ω . If it is cut into three equal parts and connected in parallel, then its total resistance is (April 2019)

(A) 6 Ω (B) 3 Ω

Ans: (B) 3 Ω

One Marks Questions

1. What is the SI unit of potential difference ? Name the device used to measure the potential difference. (June - 2020)

Ans. : Volt, Volt meter

2. Draw the symbol diagram of rheostat used in electric circuit. (June 2023)

Ans. :

Two Marks Questions

1. An electric bulb with a resistance of 50 Ω is connected to 10 V battery in an electric circuit. Calculate the electric current flowing through the electric bulb and electric power of the bulb. (June-2022)

Ans:

R = 50 Ω

V = 10

I = ?

P = ?

V = IR

I = V/R

= 10/50

= 0·2 A

Electric current flowing through bulb is 0·2A

P = VI

P = 10 × 0·2

P = 2W

Power of bulb = 2 watt = 2 W.

2. Draw the schematic diagram of an electric circuit comprising of electric cell, electric bulb, ammeter and plug key. (April - 2022)

Ans:

3. Observe the given circuit diagram.

Calculate the total resistance and the total current flowing through the circuit. ( Sep - 2020)

Ans. :

4. The resistivity of manganese wire of length 1 m is 1·84 × 10^-6 Ω m at 20°C. If the diameter of the wire is 3 × 10^-4 m, what will be the resistance of the wire at that temperature ? (June - 2020)

Ans:

5. Observe the given circuit :

Calculate the total resistance in the circuit and the total current flowing in the circuit. (June - 2020)

Ans:

6. Draw the diagram of an electric circuit in which the resistors R1, R2 and R3 are connected in parallel including an ammeter and a voltmeter and mark the direction of the current. (April 2019)

Ans:

7. According to Joule’s law of heating, mention the factors on which heat produced in a resistor depends. According to this law write the formula used to calculate the heat produced. (April 2019)

Ans:

★ The heat produced in a resistor is

i) directly proportional to the square of the current for a given resistance.

ii) directly proportional to the resistance for a given circuit.

iii) directly proportional to the time for which the current flows through the resistor.

( H = I^2RT formula is written then 2 1 mark )

8. An electric refrigerator rated 400 W is used for 8 hours a day. An electric iron box rated 750 W is used for 2 hours a day. Calculate the cost of using these appliances for 30 days, if the cost of 1 kWh is Rs. 3/-. (April 2019)

Ans:

For refrigerator,

Power, P = 400w,

P=0.4kW

Time t = 8hr, 8hr×30days = 240hrs

E = Pt,

E = 0.4 × 240 = 96kWh

Cost = 96×3 = Rs 288

For electric iron,

Power, P = 750w,

P=0.75kW

Time t = 8hr, 2hr×30days = 60hrs

E = Pt,

E = 0.75 × 60 = 45kWh

Cost = 45×3 = Rs 135

9. 1000 J of heat is produced each 2 seconds in a 5 Ω resistor. Find the potential difference across the resistor. (June 2023)

Ans:

10. A wire of given material having length ‘l’ and area of crosssection ‘A’ has a resistance of ‘4 Ω’. Find the resistance of another wire of the same material having length 1/2 and area of cross-section ‘2A’. (June 2023)

Ans. :

Three Marks Questions

1. State Joule’s law of heating. Explain the working of electric filament bulb.(June - 2020)

Ans:

★ The heat produced in a resistor is

i) directly proportional to the square of the current for a given resistance.

ii) directly proportional to the resistance for a given circuit.

iii) directly proportional to the time for which the current flows through the resistor.

( H = I^2RT formula is written then 2 1 mark )

★ A strong metal with high melting point such as tungsten is used for making bulb filaments.

★ The bulbs are usually filled with chemically inactive nitrogen and Argon gases to prolong the life of the filament.

★ Most of the power consumed by the filament appears as heat, but a small part of it is in the form of light radiated.

2. State Ohm’s law. How ammeter and voltmeter should be connected in electric circuit ? What is the use of these instruments, in the circuit ? (June - 2020)

Ans. :

★ The potential difference V across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it at constant temperature.

★ Ammeter should be connected in series.

★ Voltmeter should be connected in parallel in the circuit.

★ Ammeter is used to measure current.

★ Voltmeter is used to measure potential difference.

Four Marks Questions

1. a) State Joule’s law of heating. Name any two devices that work on the application of this law.

b) Why are the alloys like nichrome used in electrical heating devices ? (June-2022)

Ans:

The heat produced in a resistor is

i) directly proportional to the square of current for a given resistance

ii) directly proportional to the resistance for a given current

iii) directly proportional to the time for which the current flows through the resistor.

H = I2Rt

The devices that work on this law are

Electric Toaster

Electric Oven

Electric Kettle

Electric Bulb

Electric Fuse ( Any two )

★ Resistivity of alloys are more than / higher than that of metals.

★ Alloys do not oxidise ( burn ) readily at high temperature.A

★ Alloys have high melting point. ( Any two

2. a) State Ohm’s law. In domestic electric circuit electrical appliances are not connected in series. Why ?

b) Write the factors on which resistance of a conductor depends. (June-2022)

Ans :

a) The potential difference ( V ) across the ends of a given metallic wire in an electric circuit is directly proportional to the current ( I ) flowing through it, provided its temperature remains the same.

V = IR

[ 1 mark can be allotted for formula ]

★ In a series circuit the current is constant throughout the electric circuit due to this all electrical appliances not possible to work at the same value.

★ In a series connection, when one component fails, the circuit is broken.

Factors on which resistance of a conductor depends :

★ Length of a conductor

★ Area of cross-section of a conductor

★ Nature of the material

★ Temperature.

3. a) What are the advantages of connecting electrical devices in parallel in an electric circuit instead of connecting them in series ?

b) How are ammeter and voltmeter connected in an electric circuit ? What are their function ? (April - 2022, April 2019)

Ans:

Advantages of connecting electrical devices in parallel are :

★ The parallel circuit divides current through the electrical gadgets.

★When one component fails, the circuit does not fail

★ The total resistance in parallel circuit decreases, so that

★ Electrical gadgets get current as per their resistance required.

( Any two )

★ In an electrical circuit ammeter is connected in series

★ In an electrical circuit voltmeter is connected in parallel

★Ammeter measures the rate of electric current in a circuit

★ Voltmeter measures the potential difference across the ends of a conductor

4. (i) State Ohm’s law

(ii) Explain the factors on which the resistance of a conductor depend. (June 2019)

Ans:

(i) The potential difference V across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it at constant temperature.

(ii) Factors on which resistance of a conductor depends :

★ Length of a conductor

★ Area of cross-section of a conductor

★ Nature of the material

★ Temperature.

5. (i) Define electric potential difference. How is ammeter connected in an electric circuit ?

(ii) Explain the application of heating effect of electric current in an electric bulb and the fuse used in an electric circuit. (June 2019)

Ans:

(i)

★Potential difference is defined as the difference in electrical potential energy between two points.

★ An ammeter is connected in series in an electric circuit.

(ii)

★ When large electric current flow through a circuit and a large amount of heat production occurs. Due to this the fuse wire melts and the circuit breaks.

★When electric current passes through a very thin, high resistance tungsten filament of an electric bulb, the filament becomes white-hot and emits light

Five Marks Questions

1. What is the meaning of the statement “The potential difference between two points is 1 V” ? Name the device used to measure potential difference. What is resistance of a conductor ? What is electric power ? Write three formulae used to find it. (Sep - 2020)

Ans. :

★ If 1 Joule ( 1J ) of work is done to move a charge of 1 Coulomb ( 1 C ) from one point to another point in a current carrying conductor, the potential difference between the two points is 1 volt ( 1 V ).

★ The device used to measure it is voltmeter.

★ The property of a conductor to restrain or to retard the motion of electric charges flowing through it is called resistance of a conductor.

★ The rate at which electric energy is dissipated or consumed in an electric circuit is called electric power.

★ Three formulae used to find electric power are