II.10. The electrical energy and power.
The electrical energy (denoted by W) of a source measures the mechanical work done by it to move the electric charge (q) through the cross-section of the circuit, in a time interval (Δt):
W = L = E ∙ q
But q = I ∙ Δt (from the intensity formula)
W tot = E ∙ I ∙ Δt (energy consumed throughout the circuit).
W ext = U ∙ I ∙ Δt (energy consumed on a portion of the circuit).
W int = u ∙ I ∙ Δt (energy consumed on the inner circuit).
Characterization of electrical energy as a physical parameter:
Electric power (P) is a physical parameter that measures the rate of electricity transfer.
Characterization of electrical power as a physical parameter:
👀 Experiment: Measuring the electrical power of a flashlight bulb
Needed materials:
A battery of electromotive voltage equal to the nominal voltage of the bulb, a voltmeter, an ammeter, a 6.3 V bulb, connecting wires.
Experiment description:
- Make the electrical circuit shown in the following image:
- Measures the intensity of the electric current passing through the circuit and the electrical voltage at the bulb terminals.
- Calculate the power of the bulb by multiplying the voltage applied to the bulb terminals by the intensity of the current flowing through the bulb.
P = U ∙ I (measured in W)
Experiment conclusion:
The bulb lights up normally when the nominal values written on it are followed ( Un, In și Pn ).
The nominal values written on the electrical appliances are a pair of values Pn, In, Un.
Pn = Un • In