Title: Voltage, Current and Electrical Circuit
Course: Electric Circuit > Section: Simple Electric Circuit (Introduction)

Voltage, Current and Electrical Circuit

Voltage and Current

Electrical Voltage is a result of the separation of electrical charge (through work). So, voltage represents the difference of the electrical charge of two electric loaded bodies. Work is needed for the separation of the electrical charge as electrical energy is saved in the voltage. As a result, voltage can be associated with work or energy.

For measuring the voltage, the two encoders of the measuring instrument must be connected with the comparable points. If the measuring instrument is not integrated in an electrical circuit, it is called a parallel connection.

Electrical current means moving charge. It is measured through the determination of the number of the moving charges per time-unit. The averaged electrical current is calculated from the differential quotient of the charge function Q(t).

I=ΔI2−ΔI1Δt  - averaged electrical current (represented as differential quotient)

If Q(t) is the equation of the  charge-development, then electrical current is defined as differential quotient (first derivative after time).

I=dQ(t)dt=Q′(t)

For the current measurement it is necessary to implement a measuring instrument in the electrical circuit (as a result, all electric charges, which are moved in the electrical circuit, flow through the measuring instrument and can be defined. This form of circuitry of the measuring instrument is called series connection.

Simple Circuit

A simple circuit consists of:

- a current source
- a current consumer
- a current conductor

Toys and torches are always used with batteries or adaptors as current sources (safety trough low voltage).

Image: Electric circuits (symbol)
Inscription: R… Resistance (Consumer), S… Switch/Controller, A… Ampere Meter (Current Measuring Instrument)

Current consumers are for example lamps, engines and heating elements.

Because of the forward and return lines between the battery and the lamp – from the negative pole of the battery through the conductor wires and the lamp to the positive pole of the battery -, the current flows into a circuit invisibly.

Electrical current is only able to flow in a closed circuit. This means: current source, current consumer and current conductor must be connected with each other.