Q35 of 330 Page 27

The electrical resisitivities of four materials A, B, C and D are given below :

A) 110 x 10-8 Ω m


B) 1.10 x 1010 Ω m


C) 01.0 x 10-8 Ω m


D) 2.3 x 103 Ω m


Which material is : (a) good conductor (b) resistor (c) insulator, and (d) semi-conductor ?

(a) Good conductor = C (10×10-8 ohm-m)

(b) Resistor= A (110×10-8 ohm-m)


(c) Insulator= B (1×1010 ohm-m)


(d) Semiconductor= D (2.3 ×103 ohm-m)


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33

A piece of wire of resistance 20 Ω is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in the new situation.

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The electrical resistivities of three materials P, Q and R are given below :

P 2.3 x 103 Ω m


Q 2.63 x 10-8 Ω m


R 1.0 x 1015 Ω m


Which material will you use making (a) electric wires (b) handle for soldering iron, and (c) solar cells? Give reasons for your choices.

 36

The electrical resistivities of five substances A, B, C, D and E are given below :

A) 5.20 x 10-8 Ω m


B) 2.60 x 10-8 Ω m


C) 10.0 x 10-8 Ω m


D) 1.70 x 10-8 Ω m


(a) Which substance is the best conductor of electricity? Why?


(b) Which one is better conductor: A or C? Why?


(c) Which substance would you advice to be used for making heating elements of electric irons? Why?


(d) Which two substances should be used for making electric wires? Why?

 1

Give the law of combination of resistances in series.