Question

(a) What is meant by saying that potential difference between two points is 1 volt? Name a device that helps to measure the potential difference across a conductor.

(b) Why does the connecting cord of an electric heater not glow hot while the heating element does?

(c) Electrical resistivities of some substances at 20°C are given below:

Silver, 1.6 x 10^-8 Wm

Copper, 1.62 x 10^-8 Ωm

Tungsten, 5.20 x 10^-8 Ωm

Iron, 10.0 x 10^-8 Ωm

Mercury, 94.0 x 10^-8 Ωm

Nichrome, 100 x 10^-8 Ωm.

(i) Among silver and copper, which one is better conductor? 

(ii) Which material would you advice to be used in electrical heating devices? Why?

Answer 1

(a) Potential difference of 1 volt means the work done in carrying a unit positive charge from one point to another point is 1 Joule. Voltmeter is used to measure p.d. 

(b) The heating element offers higher resistance to the flow of electrons in it and glows when the current passes through it but the cord offers extremely low resistance. 

(c) (i) Silver is better conductor as its resistivity is less than copper. 

(ii) Nichrome alloy can be used to make heating devices as it offers higher resistance to the flow of current so as to convert electric energy into heat energy