Electrical energy is an important form of energy because many modern machines use it as a source of power and it can be easily converted into other forms

Electrical energy is an important form of energy because many modern machines use it as a source of power and it can be easily converted into other forms of energy.

Generators, batteries and fuel cells can produce electrical energy. Fossil fuels are generally burnt to produce electricity but other alternate means of producing electricity such as solar, wind and hydroelectric are becoming popular.

22Chapte

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electrical Quantities

Chapter 22: Electrical Quantities

Electrical energy is one of the most useful forms of energy.

Examples of electrical energy sources:

Batteries

Dynamos

stores chemical energy for conversion

converts mechanical energy to electrical energy

Electromotive force (e.m.f.)The work done by the force acting on charged particles to convert other forms of energy to electrical energy. The unit for electrical energy is joules (J)


Electrical Energy Conversions



Light Bulbsand other equipment that uses resistance filaments…

Electrical Energy

Thermal and Light Energy

The electrical current that passes through the resistance filament is very high

Large electron flow

Increase in collisions between the electrons and atoms of the filament

Atoms gain kinetic energy

Increase in temperature and hence thermal energy

Heating of coils which radiates as light

Potential Difference

Potential difference V is defined as the amount of work done W (or energy E converted) to drive a unit charge Q through any two points in a circuit.


WQV = =

E

Q

J (Joule)

C (Coulomb)V (Volt)

p.d.

charge

work done or energy converted

Potential Difference



Hence,P = IV

The SI unit of electrical power is watt (W), where 1 W is 1 J/s.

Electrical power, P, is the rate of electrical energy transformed to other forms in any electrical device.

P = E t = QV t

Rate of change of electrical energy


Electric current, I, is the rate of flow of charge, I = Q t

Cost of Electricity

We pay for the electrical energy used or converted in our homes. How much we pay depends on the power output of the electrical appliance and the period of time it is used.

As the SI unit for energy, joule (watt x second), is too small for the calculation of electricity consumed in a modern home; we use a more convenient unit called the kilowatt-hour (kWh).

Hence,

Energy used = Power x time


kilowattkWh hour

Below is the information given on a label of an electric iron.

= power x time x cost per unit

220 V to 240 V 1000 – 1200 Watts

A.C. only

Model XYZ

If electricity costs 16 cents per unit, what is the cost of using the iron at maximum power 30 minutes every day in the month of May?

Cost of electricity = energy consumed x cost per unit

= 1.2 x 0.5 x 31 x 16

= 153.6 cents

= $1.54

Sample Calculation


Turbine generators are used to produce electricity in power stations. The rotors of the turbine need a source of energy to rotate them.

1. Fuel is burned to heat water.

2. The heated water produces a high pressure steam that is used to make the turbine blades spin.

3. The turbine then drives the generator which produces electricity.

Increase in demand for electric energy

= More fossil fuels consumed

Fossil fuels


The increased rate of consumption of fossil fuels is a cause for concern as there are limited amounts of fossil fuels.

• Naturally found on earth.

• It takes millions of years to form in the ground from dead vegetation and animals.

• It is a form of non-renewable energy source (cannot be replaced).

Fossil fuels

Therefore, electricity users should conserve electricity and reduce the amount of wastage.


Conserving Electricity

Simple yet effective steps can be taken in homes to reduce the consumption of electricity

Use fans instead of air-conditioners

Use energy efficient lights

Use cold water rather than hot water

Switch off electrical appliances when not in use.

Fluorescent lamps Incandescent bulbsvs• are gas-discharge lamps that produce visible light through the production of UV light that causes the phosphor in the lamp to fluoresce

• produce light by heating up a filament, that has high electrical resistivity, until it is hot

Fluorescent lamps convert electrical energy to light energy more efficiently than incandescent bulbs.


Energy saving devices

Solar water heaters

Water heating consumes a large amount of energy.

Solar water heaters are an alternative way of heating water. Solar panels absorb heat energy from the Sun and transfers the energy to the water.

Solar water heaters also help to reduce the emission of greenhouse gases to the environment.


Energy saving devices

Hydroelectric, solar and wind energy are good alternatives to fossil fuels. They are renewable sources of energy

Hydroelectric power stations use the stored energy of water to generate electricity.

Solar-powered devices use energy from the Sun to generate electricity.

Windmills use wind power to drive generators that provide electrical energy.

Hydroelectric energy

Solar energy

Wind energy


Documents

Electrical energy is an important form of energy because many modern machines use it as a source of power and it can be easily converted into other forms