Class 10 Science Chapter 11 Question Answers - Electricity

Q1: How does the resistance of a wire change when:
(a) Its length is tripled?
(b) Its diameter is tripled?
(c) Its material is changed to one whose resistivity is three time?
Ans: (a) The resistance is tripled.
(b) The resistance is reduced by 9 times.
(c) The resistance is tripled.

Q2: If a wire is increased to 4 times its original length, by what factor does the resistivity change?
Ans: Since the resistivity depends only on the material of the wire, and not its length, it will remain the same.

Q3: If the current passing through a conductor is doubled, what will be the change in the heat produced?
Ans: Heat produced will increase by four times (H ∝ I2)

Q4: Name some devices which work on heating effect of electric current.
Ans:

• Electric bulb
• Electric iron
• Electric geyser
• Electric fuse

Q5: Why is an electric bulb filled with argon and nitrogen gas?
Ans: An electric bulb is filled with argon and nitrogen gas because they do not react with the hot tungsten filament and hence, prolong the life of the filament of the electric bulb.

Q6: State the Joule’s law of heating.
Ans: Joule’s law of heating states that the heat produced in a resistor is directly proportional to

• Square of current (I²)
• Resistance of the resistor (R) and
• Time for which the current flows through the resistor.

H = I²Rt joules
From Ohm’s law, we get H = VIt joules = v²t/R joules

Q7: How is heating effect of electric current used in an electric bulb?
Ans: Electric bulb works on the principle of heating effect of electric current. When electric current passes through a very thin, high resistance tungsten filament of an electric bulb, the filament becomes white hot and emits light.

Q8: Explain why, the filaments of electric bulbs are made of tungsten.
Ans: The filaments of electric bulbs are made of tungsten because it has a very high resistance. Due to its high resistance, heat produced is high and it becomes white-hot emitting light. Also due to its high melting point (3380° C), it can be kept white hot without melting.

Q9: A current of 4 A flows through a 12V car headlight bulb for 10 minutes. How much energy transfer occurs during this time?
Ans: Given : I = 4 A, V = 12 V, t = 10 min = 600 s
Energy transferred = VIt = 12 × 4 × 600 = 28800 J.

Q10: An electric current of 4.0 A flows through a 12 Ω resistor. What is the rate at which heat energy is produced in the resistor?
Ans: Given: I = 4 A, R = 12 Ω
Rate of production of heat energy, P = I2R = 42 × 12 = 192 W.

Q11: Calculate the energy transferred by a 5 A current flowing through a resistor of 2 Ω for 30 minutes.
Ans: Here, I = 5 A, R = 2 Ω, t = 30 min = 1800 s
Energy transferred = I2Rt = (5)2 × 2 × 1800 = 9 × 104 J.

Q12: What does the slope of V – I graph at any point represent?
Ans: Resistance.

Q13: What is the shape of the graph obtained by plotting potential difference applied across a conductor against the current flowing through it?
Ans: Straight line.

Q14: Give reason why metals are good conductors, whereas non-metals are bad conductors of electricity.
Ans:

• Metals contain free electrons which help in the conduction of electric charge and hence current
• Resistivity of metals is higher

Q15: Why are copper and aluminium wires usually employed for electricity transmission?
Ans: Copper and aluminium have low resistivities. When electricity is transmitted through copper and aluminium wires, the power losses in the form of heat are very small.