8TH GRADE · WORK AND CURRENT POWER
Thermal effect of current and safety
Joule-Lenz law, heaters, short circuits and protection.
The entire theory of the lesson is collected here; you can read it without an account. In interactive mode, the same theory appears as cards, followed by questions. with checking the answer and task, and progress is saved.
Basic Concepts
Joule-Lenz law
The amount of heat in a conductor is equal to the product of the square of the current, resistance and time.
Doubling the current quadruples the heat, so overloading the wiring is especially dangerous.
Short circuit
Connecting points in a circuit with very little resistance causes excessive current and high heat.
A fuse or circuit breaker breaks the circuit before the wires overheat and a fire occurs.
Electrical safety
Safe operation requires proper insulation, grounding, protective devices and no contact with live parts.
Wet skin conducts better, so electrical appliances should not be used with wet hands or near water without protection.
Physical quantities
Conductor heat quantity
Current energy converted into internal energy of a conductor.
Unit: joule ·
Lesson formulas
Joule-Lenz law
The heat of a conductor is equal to the square of the current multiplied by the resistance and time.
Related formulas
The same formulas in the reference, with symbols and units.
Tasks on the topic
Statements, answer options and the walkthrough.