Electricity (Part - 5) - Class 10, Physics By Lakhmir Singh PDF Download

Lakhmir Singh Physics Class 10 Solutions Page No:26

Question 1:
What happens to the resistance as the conductor is made thicker ?
Solution :
The resistance decreases.

Question 2:
If the length of a wire is doubled by taking more of wire, what happens to its resistance ?
Solution :
Resistance also gets doubled.

Question 3:
On what factors does the resistance of a conductor depend ?
Solution :
Resistance of a conductor depends on the following factors:-
Length of the conductor, area of cross section of the conductor, nature of material of the conductor and temperature of the conductor.

Question 4:
Name the material which is the best conductor of electricity.
Solution :
Silver metal.

Question 5:
Which among iron and mercury is a better conductor of electricity ?
Solution :
Iron.

Question 6:
Why are copper and aluminium wires usually used for electricity transmission ?
Solution :
Because copper and aluminium have very low resistivities.

Question 7:
Name the material which is used for making the heating element of an electric iron.
Solution :
Nichrome.

Question 8:
What is nichrome ? State its one use.
Solution :
Nichrome is an alloy of nickel, chromium, manganese ad iron having a resistivity of about 60 times more than that of copper. It is used for making the heating elements of electrical heating appliances.

Question 9:
Give two reasons why nichrome alloy is used for making the heating elements of electrical appliances.
Solution :
Nichrome alloy is used for making the heating elements of electrical appliances because:
(i) nichrome has very high resistivity
(ii) nichrome does not undergo oxidation (or burn) easily even at high temperature.

Question 10:
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?
Solution :
Because
(i) resistivity of an alloy is much higher than that of a pure metal
(ii) an alloy does not undergo oxidation (or burn) easily even at high temperature.

Question 11:
Which has more resistance :
(a) a long piece of nichrome wire or a short one ?
(b) a thick piece of nichrome wire or a thin piece ?
Solution :
(a) A long piece of nichrome wire.
(b) A thin piece of nichrome wire.

Question 12:
(a) How does the resistance of a pure metal change if its temperature decreases ?
(b) How does the presence of impurities in a metal affect its resistance ?
Solution :
(a) On decreasing the temperature, the resistance decreases.
(b) Presence of impurities in a metal increases the resistance.

Question 13:
Fill in the following blanks with suitable words :
Resistance is measured in…………….. The resistance of a wire increases as the length…………………. ; as the
temperature………. ; and as the cross-sectional area…………
Solution :
Ohms; increases; increases; decreases.

Question 14:
(a) What do you understand by the “resistivity” of a substance ?
A wire is 1.0 m long, 0.2 mm in diameter and has a resistance of 10 Ω. Calculate the resistivity of its material ?
Solution :
(a) Resistivity is the characteristic property of a substance which depends on the nature of the substance and its temperature. It is numerically equal to the resistance between the opposite faces of a 1 m cube of the substance.
(b) l = 1m
r = d/2 = 0.2/2 mm = 0.1 mm = 0.0001m,
R = 10 ohm
We know that,

Question 15:
(a) Write down an expression for the resistance of a metallic wire in terms of the resistivity.
What will be the resistance of a metal wire of length 2 metres and area of cross-section 1.55 × 10^-6 m², if the resistivity of the metal be 2.8 × 10^-8 Ωm ?
Solution :

Question 16:
(a) Give two examples of substances which are good conductors of electricity. Why do you think they are
good conductors of electricity ?
Calculate the resistance of a copper wire 1.0 km long and 0.50 mm diameter if the resistivity of copper is 1.7 × 10^-8 Ωm.
Solution :
(a) Silver and copper are good conductors of electricity because they have free electrons available for conduction.

Question 17:
Will current flow more easily through a thick wire or a thin wire of the same material when connected to the same source ? Give reason for your answer.
Solution :
Current will flow more easily through thick wire because the resistance of the thick wire will be lesser than that of thin wire.

Question 18:
How does the resistance of a conductor depend on :
(a) length of the conductor ?
(b) area of cross-section of the conductor ?
(c) temperature of the conductor ?
Solution :
(a) Resistance of a conductor increases (or decreases) with increase (or decrease) in the length of the conductor.
(b) Resistance of a conductor decreases (increases) with increase (decrease) in the area of cross-section of the conductor.
(c) Resistance of a conductor increases on raising the temperature and decreases on lowering the temperature.

Question 19:
(a) Give one example to show how the resistance depends on the nature of material of the conductor.
(b) Calculate the resistance of an aluminium cable of length 10 km and diameter 2.0 mm if the resistivity of aluminium is 2.7 x 10^-8Ωm.
Solution :
(a) If we take two similar wires of same length and same diameter, one of copper metal and other of nichrome alloy, we will find that the resistance of nichrome wire is about 60 times more than that of the copper wire. This shows that the resistance depends on the nature of material of the conductor.

Question 20:
What would be the effect on the resistance of a metal wire of :
(a) increasing its length ?
(b) increasing its diameter ?
(c) increasing its temperature ?
Solution :
(a) Resistance will increase.
(b) Resistance will decrease.
(c) Resistance will increase.

Question 21:
How does the resistance of a wire vary with its :
(a) area of cross-section ?
(b) diameter ?
Solution :
(a) By increasing the area of cross section, the resistance will decrease.
(b) By increasing the diameter, the resistance will decrease.