Amps vs volts vs ohms vs watts
Amps, volts, ohms, and watts are the basics of electrical engineering. If you have studied electrical science, electrical principles, or electronics beyond the school level then you will already be familiar with many of these concepts. On the other hand, if you are returning to study or are a newcomer to electronics or electrical technology these basic definitions will help you get up to speed. Below I did the comparison of these terms with their formulas.
Table of Contents
What is ampere?
The flow of electrical current is measured in amperes, abbreviated as “A” or “I” (Intensity of current). It may be referred to as amperage (or amp), which is the rate at which electric current flows through a conductor per second. One amp of current is approximately 6,280,000,000,000,000,000 electrons passing any particular point in a conductor per second.
An ammeter is used to measure this electrical current flow. The current must pass through the meter to measure the current. If no current is flowing, the ammeter measures “0.”
Amps measure how “fast” electricity is moving through a circuit. If equated to a river, the amps in an electrical circuit would be how fast the water in the river is moving.
Amperes can be expressed in many different ways, such as:
Quantity |
Symbol |
Decimal |
1 milliampere |
1 mA |
1/1000 A |
1 ampere |
1 A or 1 amp |
1 ampere |
1 kiloampere |
1 kA |
1000 amperes |
Formulas:
I = E / R
I = P / E
I = √P / R
E= Voltage (Volts)
I = Current (Amperes)
R= Resistance (Ohms)
P = Power (Watts)
What is volt?
The volt, abbreviated as “V” or “E” (Electromotive Force), is the unit of measure of electrical voltage (pressure) or the pressure being applied to force electrons through a circuit. Volts can be measured with a voltmeter.
Volts measure the strength of a power source (battery, wall outlet in your house). If equated to a river, the voltage of an electrical circuit would be how wide the river is.
- House outlets are between 110 and 125 volts. (in America)
- A single “AAA”, “AA”, “C”, or “D” battery are all 1 ½ volt.
- Big rectangular-shaped “lantern” batteries are 6 volts.
- Small rectangular-shaped batteries are 9 volts.
- A car battery is 12 volts.
When higher voltage is used, the device being powered will do more work. For example, a motor will turn faster, or a light bulb will give off more light. However, if you use too much voltage, the light bulb will burn out, the wire will melt, or the motor will “burn out”.
Volts can be expressed in many ways:
Quantity |
Symbol |
Decimal |
1 millivolt |
1 mV |
1/1000 volt |
1 volt |
1 V |
1 volt |
1 kilovolt |
1 kV |
1000 volts |
Formulas:
E = I x R
E = P / I
E = √P x R
E= Voltage (Volts)
I = Current (Amperes)
R= Resistance (Ohms)
P = Power (Watts)
What is ohm?
The unit of measure of electrical resistance is known as an ohm (abbreviated as “R” for resistance). The Greek letter omega (S) is used as the symbol for electrical resistance.
The movement of electrons along a conductor meets with some opposition. This opposition is known as resistance. Resistance can be useful in electrical work. Resistance makes it possible to generate heat, control current flow, and supply the correct voltage to a device.
Ohms measure how much “resistance” there is in the circuit to “slow down” the electricity. If equated to a river, the ohms in an electrical circuit are like a dam on the river. Circuits with lots of ohms need higher voltage to do the same amount of work (power a motor at the same speed for example.)
Ohms can be expressed in many ways:
Quantity |
Symbol |
Decimal |
1 ohm |
1Ω |
1 ohm |
1 kilohm |
1kΩ |
1000 ohms |
1 megohm |
1MΩ |
1,000,000 ohms |
The amount of resistance (ohm) in a conductor is determined by:
- The material of which the conductor is made
- The size of the conductor
- The length of the conductor
- Temperature
Resistance is proportional to the length and size of the conductor. If the length of the wire is doubled, the resistance is doubled. If the diameter wire is reduced by half, then the resistance is doubled. The relationship between amps (electric current), volts (electromotive force), and resistance is called Ohm’s law. Ohm’s law states that volts are equal to amperes times resistance.
Formulas:
E = I x R or I = E / R or R = E / I
E= Voltage (Volts)
I = Current (Amperes)
R= Resistance (Ohms)
P = Power (Watts)
The Ohm’s law equation can be rearranged to solve for any of the three values as long as the other two values are known. For example, the resistance in a 6-volt circuit, if 2 amperes of current are flowing in the circuit is 3 ohms.
What is watt?
Electric power is measured in watts, abbreviated as W. It may be referred to as wattage. When applied to electrical equipment, it is the rate that electrical energy is transformed into some other form of energy such as light.
Watts may be compared to the work done by water in washing a car. Keep in mind that amperes are current flow and volts are the electrical pressure. Neither amperes nor volts by themselves give a measure of the amount of power produced for turning motors or producing heat or light. For example, if 15,000 volts were available but no free electron flow or amps, there would be no power.
Also, if there were enough free electrons in a circuit to provide a flow of 3,000 amperes but no volts or pressure, there would be no power to make them flow. The following relationship exists among amperes, volts, and watts:
P = E x I
P = E² / R
P = I² x R
P = Watts
E = Volts
I = Amperes
R = Resistance
Most electrical equipment is rated in watts.
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Amps vs volts vs ohms vs watts
Function |
Term |
Symbol |
Unit of Measure |
Abbreviation |
Force |
Voltage |
E |
Volt |
V |
Result of force |
Current |
I |
Ampere |
A |
Resists current flow |
Resistance |
R |
Ohm |
Ω |
Rete of doing work |
Power |
P |
Watt |
W |