ENERGY AND ELECTRICITY In this topic we will learn about: The different types of energy. The unit we use to measure energy. The unit we use to measure power. Can energy be destroyed? What do we call the electrical energy that is not used usefully? Do you use a voltmeter in series or parallel? What can resistance be used for? Energy resources.

ENERGY Basic facts about energy: Everything needs energy to do anything. Energy is measured in Joules. Energy cannot be made or destroyed. Energy can be moved from one place to another (transferred). Energy can change form (transformed). Energy is sometimes wasted when it is transferred or transformed.

TYPES OF ENERGY Energy can exist in the following forms: Thermal (heat) Light Sound Electrical Kinetic (movement) Potential (stored):- Gravitational – in something that can fall. Elastic – in something that is stretched, compressed, bent or wound up. Chemical – in foods, fuels and batteries. Atomic – used in nuclear reactions.

ENERGY TRANSFORMATION We can use energy flow diagrams to show energy changes. Chemical energy stored in the battery is converted to electrical energy. This electrical energy is converted to heat energy in the bulb. When the bulb is hot enough it will produce light. Torch battery to bulb. light chemical electrical heat This is the INPUT – the energy we put in. This is the OUTPUT – the energy we want to get out.

ENERGY AND ELECTRICITY We can use energy flow diagrams to show wasted energy too. In the torch bulb, not all of the heat energy is transformed into light. light chemical electrical heat heat This is wasted

ENERGY AND ELECTRICITY Energy is wasted as heat whenever energy changes its form, an even better diagram would look like the one below. It shows that energy is lost at every stage. light chemical electrical heat heat In the battery. This is wasted This is wasted heat In the wiring. heat Given to the surroundings. This is wasted The thickness of the arrows shows how much energy is being transferred or wasted.

ELECTRICAL ENERGY One of the most useful forms of energy is electrical energy. It is a convenient way of moving energy from one place to another. Electrical charges have to be given energy before they can move around a circuit as an electric current. The battery (or mains supply) gives energy to the charges. This energy allows the charges to move. The more energy they are given, the bigger the current is.

VOLTAGE The voltage of an electricity supply tells you how much energy the battery can give to each charge. Voltage is measured in Volts (V) What will happen to the current in a circuit if the voltage supply is decreased? Decreasing the voltage will give the charges less energy. This means the current will be smaller.

MEASURING VOLTAGE In a circuit, there is a voltage across each component, (a component is something like a bulb). A voltmeter is used to measure voltage. The voltmeter has to be placed around (in parallel with) the component. The voltmeter is measuring the ‘voltage across the component’. V

SHARING VOLTAGE IN A SERIES CIRCUIT In a series circuit, the supply voltage is shared between the components in the circuit. This is because the charges have to pass through all the components as they pass around the circuit. 6V 6V 2V

USING VOLTAGE The brightness of a bulb in a circuit depends on how much voltage it gets. Remember - in a series circuit, the supply voltage is shared between the components in the circuit. This means that adding bulbs in series will make each bulb dimmer. 6V normal 6V 2V very dim

VOLTAGE IN A PARALLEL CIRCUIT In a parallel circuit, each charge only travels through one arm of the circuit. Because of this, each arm gets the full supply voltage. This means bulbs in parallel will be brighter. 12V 12V bright 12V 12V normal X When the charges get to X, some go along the green path and some go along the blue path. Each charge only uses one path. The charges have only one route to take.

VOLTAGE QUESTIONS Each cell in the diagrams below has a voltage of 1.5V. What will be the voltage across each bulb? The first one is done for you. 1.5V

VOLTAGE ANSWERS The voltages across each bulb are shown below: In a series circuit you need to work out the total supply voltage then divide that between the number of bulbs it is shared between. 1.5V 3V Each bulb gets 1V.

PARALLEL PROBLEMS Each cell in the diagrams below has a voltage of 1.5V. Work out the voltage across each bulb in these circuits.

PARALLEL PROBLEMS SOLVED Remember each arm will get the full supply voltage. 1.5V 0.75V 1.5V 1.5V 3V 1.5V 3V The voltage each arm gets is shared between the components in that arm.

RESISTANCE Real circuits do not just contain bulbs. They may contain resistors. The voltage will be shared between resistors in series in the same way as it is for bulbs in series. If the resistors are of different sizes, the bigger resistor will use a greater share of the supply voltage. Remember that all parts of a circuit – including bulbs and even the wires – have resistance Circuit symbol for a resistor. Resistance causes heat. This is useful in an electric heater.

ELECTRICITY IN OUR HOMES Most of the electricity we use at home comes from the mains supply. This is supplied by energy providers. The voltage of the mains supply is 240V. Mains electricity carries a lot of energy. It needs to carry a lot of energy because the electrical equipment we use at home needs energy to work. The power rating of an electrical appliance tells you how much energy it uses every second. Power is measured in Watts (W).

USING POWER The higher the power of an appliance, the more it costs to run. Different electrical appliances use different amounts of power. As a guide : Using electricity for lighting uses low power. Using electricity for movement uses medium power. Using electricity for heating uses high power.

POWER PROBLEMS Do these appliances use low, medium or high power?

SOLUTIONS TO POWER PROBLEMS High Medium Medium Low Medium High High Low

ENERGY AND ELECTRICITY Most of our electricity is made in power stations. In most power stations, fossil fuels are burned. The heat produced is used to boil water and turn it into steam. The steam then moves and turns a turbine. The turbine is connected to a generator. The generator makes electricity. Fuels burned. Water turns to steam. Steam turns turbines. Turbines turn generators. Generators make electricity. The electricity is then sent around the country to wherever it is needed. How else can electricity be made?

RENEWABLE ENERGY SOURCES Some other possibilities are: Renewable fuels such as biomass or wood could be burned to boil water and turn it into steam. Nuclear fuels can be used to make the heat needed to boil water and turn it into steam. Wind, waves and tides turn turbines which then operate generators. With geothermal energy natural steam can be used to turn turbines.

Check your learning What is the unit we use to measure energy? What is the unit we use to measure Power? Can energy be destroyed? What do we call the electrical energy that is not used usefully? Do you use a voltmeter in series or parallel? What can resistance be used for?

Check your learning - answers ENERGY is measure in JOULES. POWER is measure in WATTS. ENERGY can not be destroyed just changed from one form to another. Electrical energy that is not used usefully is called WASTED energy. VOLTMETERS are always used in PARALLEL. RESISTANCE can be used to heat up wires in ELECTRIC HEATERS.