Question

JEE MAINS PHYSICS QUESTION SEPTEMBER 2020 Find power loss in internal resistance?

Answer 1

Terminal voltage of cell (emf = 3V & internal resistance = r) is equal to 2.5 volts and heat loss in R is given by 0.5 watt.

then we have to find the power loss in internal resistance.

solution : applying Kirchoff's voltage law,

voltage across r + voltage across R = emf

⇒V_r + 2.5 V = 3 V

⇒V_r = 0.5 V

we know, power loss , P = i²R

if i remains constant, P ∝ R

but R ∝ V [ from Ohm's law ]

so, P ∝ V

so, power loss in R/power loss in r = V_R/V_r

⇒0.5 watt/power loss in r = (2.5/0.5)

⇒power loss in r = 0.1 watt

Therefore the power loss in internal resistance is 0.1 watt i.e., correct option is (3) 0.1