Electricity — Part 3: Heating effect, electric power and energy: visual lesson, CBSE Class 10 Science

Lesson

Heating, power and your electricity bill

Part 3 — why current heats a wire, how we put that to use, how fast appliances use energy (power), and how the units on your bill are counted.

In this lesson you will

Explain the heating effect of current and apply Joule’s law H = I²Rt
Explain how fuses, heaters and filament bulbs use the heating effect
Use P = VI = I²R = V²/R to solve problems
Calculate electricity consumption in kilowatt hours and its cost

Concept

Where does the heat come from?

A source does work $W = VQ$ to drive charge $Q = It$ through a resistor. With $V = IR$ , the energy given out as heat in time $t$ is $H = VIt = I^2Rt$ . This is Joule’s law of heating.

H = VIt = I^2 R t

Concept

Joule’s law: three factors

Table: heat is proportional to the square of the current, so doubling the current gives four times the heat; it is proportional to resistance and to time, so doubling either doubles the heat
Heat produced is proportional to	So, if this doubles…	Heat becomes
$I^2$ , the square of the current	Current	4 times
$R$ , the resistance (same current)	Resistance	2 times
$t$ , the time	Time	2 times

Cookies