Joule effect
Calculate the heat energy dissipated in resistive elements of a circuit.
"Power dissipated in the form of heat in the resistive elements of the circuit."
Key Formula: Joule's Law
or
Q = P × t
Where:
- Q: Heat energy (joules, J)
- I: Current (amperes, A)
- R: Resistance (ohms, Ω)
- t: Time (seconds, s)
- P: Power (watts, W)
Note: Both formulas are equivalent. Use $ Q = I^2 R t $ when you know current and resistance.
Parameter Definitions
1. Resistance (R)
The tendency of a material to oppose the flow of electric current, measured in ohms (Ω).
Higher resistance leads to more heat generation for the same current.
Example: A 100 Ω resistor limits current and produces heat.
2. Power (P)
Electrical power supplied or absorbed by a component, measured in watts (W).
1 watt = 1 joule per second.
You can calculate it as: P = I² × R or P = V × I
Example: A 5W LED uses 5 joules every second.
3. Current (I)
The flow of electric charge through a material, measured in amperes (A).
Heat is proportional to the square of the current — doubling current quadruples heat!
Example: 1 A, 2 A, 10 A — each produces vastly different heat levels.
4. Time (t)
Duration for which current flows, measured in seconds (s).
Longer time → more total heat generated.
Example: 1 second vs. 60 seconds → 60x more heat.
How It Works
When current flows through a resistor:
- Electrons move through the material
- They collide with atoms, losing kinetic energy
- This energy is transferred as vibrational energy → heat
- Total heat depends on: current, resistance, and duration
The process is irreversible — electrical energy is lost as heat.
Application Scenarios
- Designing heating elements (e.g., electric stoves, hair dryers)
- Calculating power loss in transmission lines
- Estimating temperature rise in PCB traces and components
- Selecting appropriate resistors based on power rating
- Understanding why devices get hot during operation
- Safety analysis in circuits (preventing overheating and fire risk)
