# P3.1 How much energy do we use?P3.1 How much energy do we use?

P3.1 How much energy do we use?

The global demand for energy is continually increasing. Our population is growing – we already have more people on the planet than ever before. As well as this, modern lifestyles demand transport and communications technology – which also requires more ENERGY.

This raises issues about the AVAILABILITY of energy sources and the environmental effects of using them.

A PRIMARY SOURCE of energy is one that occurs naturally. The main primary energy sources the humans use are:

• Fossil fuels (oil, gas and coal)
• Nuclear fuels
• Biofuels
• Wind
• Waves

A SECONDARY SOURCE of energy is one that is made using a primary resource. ELECTICITY is a secondary resource, and can be generated by a number of different primary sources.

FOSSIL FUELS are formed over millions of years by the decay of dead organisms. When they are burned they produce a number of pollutants. A major pollutant formed is CARBON DIOXIDE, which contributes to global warming and climate change.

When an electric current flows in a circuit, energy is transferred from the power supply to the components in the circuit. The component can then transfer energy to the environment – in the form of light, sound, heat etc. The bigger the voltage, the more energy transferred.

The POWER of an appliance tells you how FAST it transfers energy from the CHARGE passing through it – Power is usually measured in watts, W or kilowatts, kW. (1kW = 1000W)

The total energy transferred by an appliance depends on how long the appliance is on and its power rating. The formula:

Energy transferred           =              Power             x        Time

(Joules J)                                       (Watts, W)                   (Second, S)

An appliance with a high power rating transfers a lot of energy in a short time. This energy comes from the CURRENT flowing through it. This means that an appliance with a high power rating will draw a large current from the supply. The formula for electric power is

Power          =              Voltage            x        Current

(Watts, W)                           (Volts, V)                     (Amperes, A)

ENERGY is usually measured in joules. However, 1 joule is a tiny, tiny amount of electrical energy so a domestic electricity meter records how much energy you is in units of kilowatt-hours or kWh.

A KILOWATT-HOUR is the amount of electrical energy converted by a 1kW appliance left on for 1 hour. Using kilowatt-hours, the energy transfer equation becomes:

Energy transferred           =              Power             x        Time

(Kilowatt hours, kWh)                        (Kilowatts, kW)               (Hours, h)

The higher the POWER RATING of an appliance, and the longer you leave it on, the more energy it transfers – and the more it costs:

Cost                       =             Number of kWh               x        Cost per kWh

Energy cannot be created or destroyed. It can only be transferred from one form to another. Energy that is “WASTED” like the heat energy from an electric lamp does not disappear. Instead, it is TRANSFERRED to its surroundings and spreads out so much that it becomes difficult to do anything useful with it.

E.g. Ordinary electric lamps contain a thin metal filament that glows when electricity passes through it. However, most of the electrical energy is transferred as heat rather than light energy. This is the SANKEY DIAGRAM for a typical filament lamp:

The EFFICIENCY of a device / electrical appliance can be calculated using the formula:

As the world’s population continues to grow, more and more energy is needed for fuel and power. The FOSSIL FUELS we rely on most of our energy are pretty bad for the environment and will eventually run out. We can all help the situation by reducing the amount of energy we use every day.