question_answer

 

(a) Write two points of difference between electric energy and electric power.

(b) Out of 60 W and 40 W lamps, which one has a higher electrical resistance when in use.

(c) What is commercial unit of electric energy? Convert it into Joules.

Answer:

(a)
Sr. No.	Electric energy	Electric power
(i)	Electrical energy consumed by an electrical appliance is given by the product of its power rating and time for which it is used.	It is the rate at which electrical energy is consumed.
(ii)	It is measured in kWh.	It is measured in watt or kilowatt.
(b) Power \[(P)=\frac{{{V}^{2}}}{R}\]
i.e. At same voltage, power (P) is inversely proportional to resistance (R).
‹ 40 W lamp has higher resistance.
(c) The commercial unit of electrical energy is kWh.
1 kWh = 1000 W \[\times \] 1hr = 1000 W \[\times \] 3600s
\[=36\mathrm{ }\times \mathrm{ }{{10}^{5}}\mathrm{ }Ws\]
\[=3.6\mathrm{ }\times {{10}^{6}}\mathrm{ }J\]