Measurements of Electricity

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How to Measure Electricity

Voltage is the electrical difference that can occur between two poles of electric current. The common AA battery is an excellent example of how the difference in electricity, or voltage, is measured at the positive and negative poles. The standard measurement of voltage is volts, usually indicated by the letter “V”.

Current refers to the electrons flowing in an electric circuit. Its measurement is usually in amperes or amps, indicated by the letter “A”.  The ampere is the system of unit (SI) for measuring electrical current, which uses the “I” symbol. The amount of current flowing into any appliance can be checked on its power supply.

Resistance refers to the force that opposes the flow of electrical current. Its standard measurement is Ohms, with the ‘W [T1] ’ symbol.

Power is the energy conversion rate measurement. It is measured in watts, which is indicated by the letter “W” and represented by the symbol “P”. This measurement is displayed on any electric appliance. The higher the number of watts is the greater the amount of electricity that will be consumed by the electric appliance. However, the appliance’s performance will normally be faster and more efficient.

Energy is the work capacity of electricity; its formula is time multiplied with power. Energy is denoted by the “E” symbol, with its measurement in joules. One joule of energy per second = one watt of power. Electrical energy is normally denoted by watt hours, or kilowatt hours (kWh); one kWh = 1,000 watt hrs.

Volts, amps, ohms, watts and watt hours relationship

Power

Volts x Current = Power

V x I = P

The formula for power is volts multiplied by current. For example, an electric appliance that uses a 12-volt circuit and a 4-amp current gives 48 watts of power. (4 x12 = 48)

This formula shows that voltage can be calculated when the values of current and power are known. Or current can be computed if power and voltage values are known.

Power  ¸ Current = Volts

P ¸ I = V

For instance, a 48-watt motor with 4 amps of current will use 12 volts.

48 ¸ 4=12

Alternatively, a 48-watt motor with a 12 volt supply requires a 4 amp current.

Current = Power ¸ Volts

I = P ¸ V

48 ¸ 12 = 4

Volts

Current x Resistance = Volts

I x r = V

The formula for voltage is the current multiplied by the resistance, giving the renowned Ohm's Law. This formula can be expressed in various forms: resistance can be calculated if current and voltage are known, current can be computed if resistance and voltage values are known.

Volts ¸ Resistance = Current

V¸ r = I

Volts ¸ Current = Resistance

V¸ I = r

Power

Current2 x Resistance = watts

I2 x r = P

Power, which is measured in watts, has the formula above – the square of the current multiplied by the resistance.


Once you understand the basic rules of electricity, your solar electric system is easier to manage.