BASIC ELECTRICAL QUANTITIES CURRENT, VOLTAGE, RESISTANCE, POWER, CHARGE, EFFICIENCY

BASIC ELECTRICAL CONCEPTS AND TERMS - CURRENT, VOLTAGE, RESISTANCE, POWER, CHARGE, EFFICIENCY.

ELECTRICAL VOLTAGE.

Electrical voltage is defined as electric potential difference between two points of an electric field.

In an electrical circuit, the electrical voltage V in volts (V) is equal to the energy consumption E in joules (J)

divided by the electric charge Q in coulombs ©.

v= e/q

• V is the voltage measured in volts (V)
• E is the energy measured in joules (J)
• Q is the electric charge measured in coulombs (C)

ELECTRIC CURRENT

Electrical current is the flow rate of electric charge in electric field, usually in electrical circuit.

Electrical current is measured by the rate of electric charge flow in an electrical circuit:

i(t) = dQ(t) / dt

The momentary current is given by the derivative of the electric charge by time.

• i(t) is the momentary current I at time t in amps (A).
• Q(t) is the momentary electric charge in coulombs (C).
• t is the time in seconds (s).

ELECTRICAL RESISTANCE

Resistance is an electrical quantity that measures how the device or material reduces the electric current flow through it.

The resistance is measured in units of ohms (Ω).

The resistance of a conductor is resistivity of the conductor's material times the conductor's length divided by the conductor's cross sectional area.

R=ρ*l/a

• R is the resistance in ohms (Ω).
• ρ is the resistivity in ohms-meter (Ω×m)
• l is the length of the conductor in meter (m)
• A is the cross sectional area of the conductor in square meters (m²)

ELECTRIC POWER

Electric power is the rate of energy consumption in an electrical circuit.

The electric power is measured in units of watts.

The electric power P is equal to the energy consumption E divided by the consumption time t:

P= E X t

• P is the electric power in watt (W).
• E is the energy consumption in joule (J).
• t is the time in seconds (s).

ELECTRIC CHARGE

Electric charge generates electric field. The electric charge influence other electric charges with electric force and influenced by the other charges with the same force in the opposite direction.

There are 2 types of electric charge:

POSITIVE CHARGE (+)

1. Positive charge has more protons than electrons (Np>Ne).
2. Positive charge is denoted with plus (+) sign.
3. The positive charge attracts other negative charges and repels other positive charges.
4. The positive charge is attracted by other negative charges and repelled by other positive charges

NEGATIVE CHARGE (-)

1. Negative charge has more electrons than protons (Ne>Np).
2. Negative charge is denoted with minus (-) sign.
3. Negative charge attracts other positive charges and repels other negative charges.
4. The negative charge is attracted by other positive charges and repelled by other negative charges.

COULOMB UNIT

The electric charge is measured with the unit of Coulomb [C].

One coulomb has the charge of 6.242×10¹⁸ electrons:

1C = 6.242×10¹⁸ e

ELECTRIC POWER EFFICIENCY

Power efficiency is defined as the ratio of the output power divided by the input power:

η = 100% ⋅ P_out / P_in

• η is the efficiency in percent (%).
• P_in is the input power consumption in watts (W).
• P_out is the output power or actual work in watts (W).

ENERGY EFFICIENCY

Energy efficiency is defined as the ratio of the output energy divided by the input energy:

η = 100% ⋅ E_out / E_in

• η is the efficiency in percent (%).
• E_in is the input energy consumed in joule (J).
• E_out is the output energy or actual work in joule (J).

POWER FACTOR

1. In AC circuits, the power factor is the ratio of the real power that is used to do work and the apparent power that is supplied to the circuit.
2. The power factor can get values in the range from 0 to 1.
3. When all the power is reactive power with no real power (usually inductive load) - the power factor is 0.
4. When all the power is real power with no reactive power (resistive load) - the power factor is 1.