Read the following and answer any four questions from 18(i) to 18(iv) Electrical Resistivity and its inverse,electrical conductivity are fundamental properties of a material that quantifies how strongly it resists or conducts electric current.A low resistivity indicates a material that readily allows electric current to flow.Resistance is defined as the ratio of potential difference across a conductor to the current passing through it.Resistance is the property of a conductor to resist the flow of charges through it. Both resistance and resistivity describe how difficult it is to make electric current flow through a material, but unlike resistance ,resistivity is an intrinsic property.This means that all pure copper wires irrespective of their shape and size,have the same resistivity, but a long,thin copper wire has a much larger resistance then a thick,short copper wire.Every material has its own characteristic resistivity. For example,rubber has a far larger resistivity than copper.Resistivity of metals also varies with temperature.The resistance of almost all alloys increases with increase in temperature but the rate of change of resistance is less than that of metals. In fact the resistance of certain alloys such as Menganin and Eureka show practically no change in resistance to a considerable range of temperature.
Your answer
(i) What happens to resistivity of a wire if it is stretched? *
it will increase
it will decrease
first increases then decreases
remains same
(ii) Though silver is a good conductor, why it is not an ideal choice for transmission of electricity? (1)it is expensive (2)it oxidize and tarnishes when it comes in contact with air (3)its resistivity decreases with increase in temperature *
only (1)
only (2)
both (1)and (2)
only (3)
(iii) The area of cross section of a wire becomes half when its length is stretched to double. How is the resistance of the wire is affected in the new condition? *
resistance of the wire remains unchanged
resistance of the wire decreases to half
resistance of the wire increases to double
The resistance of the wire increases four times
(iv) If there are two wires, w1 and w2 of same material and same length but have radius r and 2r respectively, then which wire will have more resistance? *
wire w1 has more resistance as compared to w2
wire w2 has more resistance as compared to w1
both the wires have same resistance
wire w2 has three times resistance than wires w1
Answers
Answer:
A low resistivity indicates a material that readily allows electric current to flow.Resistance is defined as the ratio of potential difference across a conductor to the current passing through it.Resistance is the property of a conductor to resist the flow of charges through it. Both resistance and resistivity describe how difficult it is to make electric current flow through a material, but unlike resistance ,resistivity is an intrinsic property.This means that all pure copper wires irrespective of their shape and size,have the same resistivity, but a long,thin copper wire has a much larger resistance then a thick,short copper wire.Every material has its own characteristic resistivity. For example,rubber has a far larger resistivity than copper.Resistivity of metals also varies with temperature.The resistance of almost all alloys increases with increase in temperature but the rate