Q1 of 330 Page 37

Give the law of combination of resistances in series.

When resistors are joined from end to end, it is called in series. In this case, the total resistance of the system is equal to the sum of the resistance of all the resistors in the system.


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35

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 ?

 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?

 2

If five resistances, each of value 0.2 ohm, are connected in series, what will be the resultant resistance?

 3

State the law of combination of resistances in parallel.