KS4 Physics Energy Transfers

Energy Transfers Useful energy Conservation of energy Wasted energy Contents Energy Transfers Useful energy Conservation of energy Wasted energy Efficiency Summary activities

Useful energy transfer Many everyday objects are designed to transfer energy from one form into another useful form. What energy transfer is an electric fan designed to carry out? electrical energy kinetic energy

What is the useful energy transfer? What energy transfer is a speaker designed to carry out? electrical energy sound energy

What is the useful energy transfer? What energy transfer is a wind farm designed to carry out? Acknowledgement © Energy Northwest/DOE/NREL Turbine installation at the Nine Canyon Wind Project; largest wind farm to be built in Washington State. kinetic energy electrical energy

What is the useful energy transfer? What energy transfer is a hydroelectric power station designed to carry out? gravitational energy electrical energy

Useful energy transfers Complete the input and useful output energies for the devices in this table. Device Input energy Output energy kettle solar cell catapult coal fire electrical heat light electrical elastic kinetic chemical heat

Energy Transfers Useful energy Conservation of energy Wasted energy Contents Energy Transfers Useful energy Conservation of energy Wasted energy Efficiency Summary activities

Law of conservation of energy All energy transfers follow the law of conservation of energy: Energy cannot be created or destroyed, just changed in form. This means that energy never just ‘disappears’. The total amount of energy always stays the same, i.e. the total input energy = total output energy. In most energy transfers, the energy is transferred to several different forms, which may be useful or not useful. The energy which is transferred to unwanted forms of energy is wasted.

Energy transfer in a television An energy transfer diagram shows the input energy and the output energies for a device. This includes all the useful and wasted forms of energy. For example, in a television: light electrical sound heat

Energy transfer in a radio What are the main energy transfers in a radio? (Don’t forget the wasted energy.) sound electrical heat

Energy transfer in a car engine What are the main energy transfers in a car engine? (Don’t forget the wasted energy.) kinetic chemical sound heat

Identifying energy transfers Question 1: An electric light bulb Input: electrical Output: light, heat Question 2: A girl cycling along a road Input: chemical Output: kinetic, heat, sound Question 3: A solar panel Input: light Output: electrical Question 4: Firing a catapult Input: elastic Output: kinetic, sound Question 5: An aeroplane taking off Output: kinetic, sound, heat, gravitational Question 6: Winding up a clockwork toy Input: kinetic Output: elastic, sound

Falling objects When an object falls in a gravitational field: Gravitational potential energy (GPE) at the top equals the kinetic energy (KE) of the object just before it hits the ground. If a diver has 4 000 J of GPE at the top of a cliff, how much KE will she have just before she hits the sea? _________ 4 000 J Assuming no energy is lost by air resistance!!!

Gerald the Human Cannonball

Energy Transfers Useful energy Conservation of energy Wasted energy Contents Energy Transfers Useful energy Conservation of energy Wasted energy Efficiency Summary activities

Wasted energy Whenever energy is changed from one form to another, some energy is always wasted. Energy is usually wasted as: heat energy; sound energy. All electrical devices produce a small amount of heat energy which is normally wasted.

car engine hairdryer jet engine washing machine Wasted sound energy If you can hear a device that is not designed to make noise then energy is wasted as sound. Examples of devices which waste energy as sound include: car engine hairdryer jet engine washing machine

car engine television mobile phone charger radio Wasted heat energy If a device gets warm and it is not designed to get warm then energy is wasted as heat. Examples of devices which waste energy as heat include: car engine television mobile phone charger radio

Which type of energy is wasted?

What happens to wasted energy? What happens to the wasted energy produced whenever energy is changed from one form to another? (Remember energy cannot be created or destroyed.) Wasted energy spreads out into the surroundings – this is called dissipated energy. This dissipated energy is too spread out to do useful work and so cannot be re-used. This is why it is important to reduce the amount of energy that is wasted.

Energy Transfers Useful energy Conservation of energy Wasted energy Contents Energy Transfers Useful energy Conservation of energy Wasted energy Efficiency Summary activities

Energy efficiency Efficiency is a measure of how good a device is at changing energy from one form to another. All devices waste energy, so the efficiency of a device is never 100%. The more efficient a device is the less energy is wasted. Energy efficient light bulbs are more efficient than normal light bulbs because they w____ less energy. More of the e_______ energy that they are supplied with is converted into l____ energy and not h___. aste lectrical ight eat

Calculating efficiency The efficiency of a device can be calculated using this formula : efficiency = useful energy out total energy in Useful energy is measured in joules (J). Total energy is measured in Joules (J). This means that efficiency does not have any units. It is a number between 0 and 1 or a percentage.

Efficiency of a bulb This filament bulb is supplied with 100 J of electrical energy which it converts to 45 J of light energy. Wasted energy = Total – Useful = 100 J – 45 J = 55 J How much energy is wasted? In what form is the energy wasted? What is the efficiency of the bulb? 55 J heat Efficiency = Useful Total = 45 J 100 J = 0.45 or 45% 0.45 or 45%

Efficiency of a radio This radio is supplied with 300J of electrical energy which it converts to 96J of sound energy. Wasted energy = Total – Useful = 300 J – 96 J = 204 J How much energy is wasted? In what form is the energy wasted? What is the efficiency of the radio? 204 J heat Efficiency = Useful Total = 96 J 300J = 0.32 or 32% 0.32 or 32%

Efficiency of a television This television converts 2 000J of electrical energy into useful energy at an efficiency of 65%. What useful energy does a television produce? How much useful energy is produced? light and sound Efficiency = Useful Total Useful = Efficiency x Total = 0.65 x 2 000 J = 1 300 J 1 300 J

Efficiency questions

Energy Transfers Useful energy Conservation of energy Wasted energy Contents Energy Transfers Useful energy Conservation of energy Wasted energy Efficiency Summary activities

dissipated – Energy that spreads out into its surroundings Glossary dissipated – Energy that spreads out into its surroundings so that it is no longer useful. efficiency – A measure of how good a device is at changing energy from one form to another. energy transfer – The process of changing energy from one form into another. input energy – The energy going into a device. output energy – The forms of energy produced by a device. useful energy– Energy in a form which is wanted. wasted energy – Energy in a form which is not wanted or is not used.

Anagrams

Energy transfers – summary

Multiple-choice quiz