Power Dissipation

Power in a Resistor

When current flows through a resistor, electrical energy is converted to heat. The power dissipated is:

P = I² · R

Using Ohm's law (V = IR), there are three equivalent forms:

P = I² · R       (use when you know I and R)
P = V² / R       (use when you know V and R)
P = V · I        (use when you know V and I)

Unit: Watt (W)

1 Watt = 1 Joule per second = 1 Volt × 1 Ampere

Resistor Ratings

Resistors have a power rating — the maximum power they can safely dissipate (commonly 1/8W, 1/4W, 1/2W, 1W). Exceed it and they fail or catch fire.

Before choosing a resistor, always verify:

P_calculated < P_rating

With a 2× safety margin is good practice.

Examples

Energy Over Time

If the power is constant, energy consumed in time t:

E = P · t    (joules, if P in watts and t in seconds)

Your Task

Implement double power_dissipated(double i, double r) that returns the power dissipated as P = I² · R.