a) Write Joule’s law of heating.
b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to the electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V

Solution

a) Joule's Law of Heating states that the amount of heat produced in a conductor is directly proportional to the square of current passing through it, directly proportional to the resistance of the conductor, directly proportional to the time for which current passed i.e

$H \propto I^{2} . . . (i) H \propto R . . . (i i) H \propto t . . . . (i i i) c o m b i n i n g (i), (i i) a n d (i i i) H \propto I^{2} R t J o u l e$

b) Resistance of first lamp = R₁
Resistance of second lamp =R₂

$R = \frac{V^{2}}{P}, R_{1} = \frac{220 x 220}{100} = 48 Ω R_{2} = \frac{220 x 220}{60} = \frac{2420}{3} Ω T h e y a r e c o n n e c t e d i n p a r a l l e l \frac{1}{R} = \frac{1}{R_{1}} + \frac{1}{R_{2}} = \frac{1}{484} + \frac{3}{2420} R = \frac{484 x 2420}{3 (484 + \frac{2420}{3})} = \frac{605}{2} Ω$

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Electricity

a) Write Joule’s law of heating.
b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to the electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V

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For Daily Free Study Material Join wiredfaculty

Electricity

a) Write Joule’s law of heating.b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to the electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V

Some More Questions From Electricity Chapter

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

a) Write Joule’s law of heating.
b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to the electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V