Question

When a flashlight is operated, what is being used up: battery current, battery voltage, battery energy, battery power, or battery resistance? Explain your reasoning. On the other hand, the equation of power P = V²/R indicates that the power dissipated in a resistor of the flashlight decreases if the resistance is increased, whereas the equation P = I²R implies the opposite. Is there a contradiction here? Explain.

Answer 1

Energy is stored in battery.

When flashlight is operated, this electrical energy is converted into light energy.

so when flashlight is operated, battery energy is being used up.

We have, P = I2R

Also, P = V2/R

In the second case, when resistance is increased, power decreases.

But in first case, when resistance is increased power also increases.

But at the same time, current (I) is decreased since current in inversely proportional to resistance (Ohm's law).

So net power remains the same.

So there is no contradiction there.

(If you have any doubts, comment down below)