ELECTRICAL QUANTITIES

- Voltage or potential difference.
The amount of energy that generator can transfer the electrons depends on its voltage (V). This is measured in volts (V).
We can use a voltmeter to measure the voltage. This device has two wires that must be connected in parallel to the element that we are checking.

- Measuring electric current.
Electric current (I) is the charge or number of electrons that flow through the cross-section of a conductor every second. 
I = Q/t
Electric current is measured in amperes or amps (A).
We can use an ammeter to measure electric current. This instrument is connected in series, so that all the electrons must pass through it.

- Electrical resistance: Ohm's Law.
The resistance (R) of a material is equal to the voltage divided by the intensity of the electric current wich travels through the material. Is called Ohm's Law, can be expressed as follows: R = V/I
The Ohm's Law has two forms: V = R x I  and  I = V/R


- Electrical energy and power.
· Electrical energy.
If an electrical current (I) flows at a particular tension (V) for a certain amount of time (t), we can calculate the energy (E) that is consumed: E = V x I x t
This electrical energy is measured in joules (J).

· Electric power.
If an electric current (I) flows at a particular tension (V), we can calculate the power (P) that is consumed: P = V x I
Electric power is measured in watts (W) or kilowatts (kW).
We can calculate the electrical energy that it consumes over a certain amount of time: 
E = P x t