Question

i )Write Joule's law of heating.
(ii) Two lampsare rated 100w and 220 V and the other 60 w 220V is connected in parallel
to electric main supply. Find the current drawn by two bulb from the line. If the
supply voltage is 220V.
​

Answer 1

Answer:

H = I^2*R*T

Explanation:

ii)

Lamp 1 = 100W/220v

Lamp 2 = 60 W/220v

Resistance of lamp 1 is calculated as:

P = V^2/R

or R1 = V^2/ P

= (220 * 220) / 100

= 484 ohm

Resistance of lamp 2 :

R2 = V^2 / P

= (220 * 220) / 60

= 806.66 ohm

Current taken by Lamp 1 *

V = I1 * R1

V/R1 = I1

220 / 484 = I1

or I1 = 0.45 A

Current taken by Lamp 2 *

V = I2 * R2

V/R2 = I2

I2 = 220/806.66

or I2 = 0.27A

* The following was done by ohm's law

Answer 2

H= I²RT

in case of lamp 1

v=220v

p= 100w

p= v²/R

R= v²/p

= 484ohm

again

V= IR

I= V/R

= 220/484=0.45A

in case of lamp 2

R=v²/p

= 220²/60= 806.66ohm

I= v/R

= 220/806.66

= 0.27A

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