The words “power” and “energy” are often used interchangeably. While energy in the ability to do work, power is the rate at which energy is transferred, used, or transformed.

### Barrel of oil

Barrel is unit of measurement of volume. Generally, it is used to describe the production or consumption of crude oil by any entity. 1 barrel of oil (1 bbl) = 42 US gallon = 159 litres.

### Calorie

The approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius. This unit is used for measuring heat energy. One calorie is equal to 4.184 joules. It is often used instead of joules when dealing with the energy released from food.

### Horsepower

A unit for measuring the rate of work (or power) equivalent to 33,000 foot-pounds per minute or 746 watts. The mechanical horsepower, also known as imperial horsepower, of exactly 550 foot-pounds per second is approximately equivalent to 745.7 watts.

### Joule (J)

A standard International System of Units of energy; 1055 Joules is equal to 1 BTU.

### Kilowatt-hour (kWh)

A unit of energy equal to one kW applied for one hour; running a one kW equipment for one hour would dissipate one kWh of electrical energy as heat. The kilowatt-hour (symbolized kWh) is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour (1 h) of time. 1 kWh = One thousand watt hours.

### Kilowatt (kW)

One thousand watts of electricity.

### Megajoule (MJ)

One million Joules.

### Megawatt (MW)

One Million Watts; a modern coal plant will have a capacity of about 1,000 MW.

### Unit of electricity

1 unit of electricity = 1 kWh. The electricity used is generally charged for in “unit of electricity’. Killowatt-hours is the product of watts x time (one killowatt = 1000 watts). A two killowatt heater switched on for three hours will have used six killowatt-hours of electricity.

### Volt (V)

The volt is the International System of Units (SI) measure of electric potential or electromotive force. A potential of one volt appears across a resistance of one ohm when a current of one ampere flows through that resistance.

### Watt (Electric)

The electrical unit of power. The rate of energy transfer equivalent to 1 ampere of electric current flowing under a pressure of 1 volt at unity power factor.

### Watt (Thermal)

A unit of power in the metric system, expressed in terms of energy per second, equal to the work done at a rate of 1 joule per second.

### Watthour (Wh)

The electrical energy unit of measure equal to 1 watt of power supplied to, or taken from, an electric circuit steadily for 1 hour.

**Source : Portal content team**

If a calorie is the amount of energy to raise one gram of water through one degree Celsius how do you define, in quantitative terms, a unit of energy?