Question

Read the following and answer any four questions from 19 (i) to 19 (v)
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 electrical current flow through a material, but unlike resistance, resistivity is an intrinsic property. This means 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 than a thick, 
short copper wire, Every material has its characteristic resistivity. For example, rubber has a far larger resistivity than copper. The resistivity of metals also varies with temperature. 
The resistance of almost all alloys increases with an increase in temperature but the rate of change of resistance is less than that of metals. The resistance of certain alloys such as Magnesium, Eureka, and Constantan show practically no change in resistance to a considerable range of temperature.
 
(18.1) What happens to the resistivity of a wire if it is stretched?
             (a) It will increase                                    (b) it will decrease 
            (c) First increases then decreases         (d) remains the same
            
(18.2) Though silver is a good conductor, why It is not an ideal choice for the                 transmission of electricity?
(1)   It is expensive
(2)   It oxidizes and tarnishes when it comes in contact with air
           (3). Its resistivity decreases With the increase in temperature
             
           (a) Only 1    (b) Only2   (c) Both   l and 2   (d) Only 3
 
(18.3) The area of cross-section of a wire becomes halt when its length is stretched to            double. How the resistance of the Wire is affected in the new Condition?
(a)   Resistance of the wire remains unchanged
(b)  Resistance of the wire decreases to half
(c)    Resistance of the wire increases to double
(d)  Resistance of the wire increases four times
(18.4)  If there are two Wires, W1, and W2, of the same material and same length but               have radius “r’ ‘ and “2r “respectively, then which wire will have more                   resistance 
(a)   Wire W1, has more resistance as compared to W2,
(b)  Wire W2, has more resistance as compare to W1
(c)    Both the wires have the same resistance
(d)  Wire W2, has three times the resistance than wire W1
 
(18.5) Ajay made the following conclusions regarding the resistance of metals/alloy.  
           Which one would you disagree with?
(a)  The resistivity of a metal decreases with temperature
(b)  A thick copper wire has less resistance than a thin copper wire of the same              length.
         (c)Alloys are often used in the manufacture of standard resistors
         (d) Low resistivity means the material easily allow the flow of electric current.
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