Question

Give Scientific reasons.
a. Tungsten metal is used to make a solenoid type coil in an electric bulb.
b. In the electric equipment producing heat e.g. iron, electric heater, boiler, toaster etc, an alloy such as Nichrome is used, not pure metals.
c. For electric power transmission, copper or aluminium wire is used.
d. In practice the unit kWh is used for the measurement of electrical energy, rather than joule.

Answer 1

a. Tungsten metal is used to make a solenoid type coil in an electric bulb because its melting point is very high. Thus, when a high amount of current is passed through it, it becomes red hot and emit lights without getting burnt.

b. In the electric equipment producing heat, such as iron, electric heater, boiler, toaster etc., an alloy such as Nichrome is used, not pure metals because of the following reasons:
(i) Resistivity of Nichrome is more compared to pure metal.
(ii) Melting point of Nichrome is high as compared to pure metal.
(iii) Nichrome does not get oxidised when heated in air whereas metal does.

c. ​For electric power transmission, Copper or Aluminium wire is used because they provide low resistance path to the flow of current. Thus, the power loss in the low resistance transmission wire will be less.

d. In practice, the unit kWh is used for the measurement of electrical energy, rather than joule. This is because joule is a very small unit and the energy consumption in day to day life is very large i.e. it comes in figures of 10⁶ to 10⁸. Thus, to reduce the complexity of handling such large figures, a bigger unit was required. This bigger unit used for the measurement of electrical energy is kWh and is related to joule as
1 kWh = 3.6 $\times$ 10⁶ J
Hence, the energy reading commercially became simpler by using this bigger unit instead of joule.