OCR 21 st Century Science Unit P3a Revision Sustainable energy

02/09/2015 Energy Consumption The demand for energy is predicted to rise by a large amount in the next few decades: What issues will this rise in demand cause?

02/09/2015Fuels A “fuel” is something that can be burned to release heat and light energy. The main examples are: Coal, oil and gas are called “fossil fuels”. In other words, they were made from fossils.

02/09/2015 Some definitions… A renewable energy source is clearly one that can be _______ (“renew = make again”), e.g. _____, solar power, biogas etc. A ___________ energy source is one that when it has been used it is gone forever. The main examples are ____, oil and gas (which are called ______ ____, as they are made from fossils), and nuclear fuel, which is non-renewable but NOT a fossil fuel. Electricity is called a “________ source” because it is converted from other forms – what would these forms be in batteries, wind turbines and solar panels? Words – non-renewable, coal, fossil fuels, wood, renewed, secondary

02/09/2015Pollution When a fuel is burned the two main waste products are _____ dioxide and ________ dioxide. Carbon dioxide is a _________ ___ and helps cause _______ _________. This is produced when any fossil fuels are burned. Sulphur dioxide, when dissolved in ________, causes ______ _____. This is mainly a problem for ___ power stations. Nuclear power stations do not produce these pollutants because they don’t ____ fossil fuels. Words – sulphur, coal, global warming, carbon, acid rain, greenhouse gas, rainwater, burn

02/09/2015 Using Electricity Basically, electrical devices are used to transfer electrical energy to the environment: -+ This light bulb will transfer light and heat to the surroundings.

02/09/2015 Energy and Power The POWER RATING of an appliance is simply how much energy it uses every second. In other words, 1 Watt = 1 Joule per second E TP E = Energy (in joules) P = Power (in watts) T = Time (in seconds)

02/09/2015 Some example questions 1)What is the power rating of a light bulb that transfers 120 joules of energy in 2 seconds? 2)What is the power of an electric fire that transfers 10,000J of energy in 5 seconds? 3)Rob runs up the stairs in 5 seconds. If he transfers 1,000,000J of energy in this time what is his power rating? 4)How much energy does a 150W light bulb transfer in a) one second, b) one minute? 5)Jonny’s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a 50 minute physics lesson? 6)Lloyd’s brain, being more intelligent, only needs energy at a rate of about 20W. How much energy would his brain use in a normal day? 60W 2KW 150J, 9KJ 120KJ 630MJ 0.2MW

02/09/2015 Power Power is “the rate of doing work”. The amount of power being used in an electrical circuit is given by: P IV Power = voltage x current in W in V in A We can use this equation to analyse power stations: 1)A transformer gives out 10A at a voltage of 50V. What is its power output? 2)An electric fire has a power rating of 2KW. If it runs on a voltage of 230V what is the current? 3)Electricity is transmitted along some lines in the National Grid at 400KV. If the current is 1KA what would be the power through the wire? 500W 8.7A 400MW

02/09/2015 The Cost of Electricity Electricity is measured in units called “kilowatt hours” (kWh). The kilowatt hour is a unit of energy but the Joule is too small to count so we use the KWh instead. For example… A 3kW fire left on for 1 hour uses 3kWh of energy A 1kW toaster left on for 2 hours uses 2kWh A 0.5kW hoover left on for 4 hours uses __kWh A 200W TV left on for 5 hours uses __kWh A 2kW kettle left on for 15 minutes uses __kWh

02/09/2015 The Cost of Electricity To work out how much a device costs we do the following: Cost of electricity = Power (kW) x time (h) x cost per kWh (p) For example, if electricity costs 8p per unit calculate the cost of the following… 1)A 2kW fire left on for 3 hours 2)A 0.2kW TV left on for 5 hours 3)A 0.1kW light bulb left on for 10 hours 4)A 0.5kW hoover left on for 1 hour 48p 8p 4p

02/09/2015 Reading Electricity Meters 1)How many units of electricity have been used? 2)If 1 unit costs 10p how much has this electricity cost? 1 month later…

02/09/2015 The 9 types of energy Type3 example sources Heat Kinetic (movement) Nuclear Sound Light Chemical Electrical Gravitational potential Elastic potential Type3 example sources

02/09/2015 The Laws of Physics There are many laws of physics, but one of the most important ones is: Energy cannot be created or destroyed, it can only be converted from one form to another

02/09/2015 Energy changes To describe an energy change for a light bulb we need to do 3 steps: Electricity Light + heat 1) Write down the starting energy: 3) Write down what energy types are given out: 2) Draw an arrow What are the energy changes for the following…? 1)An electric fire 2)A rock about to drop 3)An arrow about to be fired

02/09/2015 Conservation of Energy In any energy change there is ALWAYS some “waste” energy: e.g. a light bulb: In this example HEAT is wasted and it is transferred to the surroundings, becoming very difficult to use. ElectricityLight + heat Describe the following energy changes and state the “waste” energy or energies: 1)A vacuum cleaner 2)A TV 3)A dynamo/generator

02/09/2015Efficiency Efficiency is a measure of how much USEFUL energy you get out of an object from the energy you put INTO it. For example, consider a TV: Electrical Energy (200J) Light (80J) Sound (40J) Heat (?) Efficiency = Useful energy out Energy in x100%

02/09/2015 Some examples of efficiency… 1)5000J of electrical energy are put into a motor. The motor converts this into 100J of movement energy. How efficient is it? 2)A laptop can convert 400J of electrical energy into 240J of light and sound. What is its efficiency? Where does the rest of the energy go? 3)A steam engine is 50% efficient. If it delivers 20,000J of movement energy how much chemical energy was put into it? 0.2 or 20% 0.6 or 60% 40KJ

02/09/2015 Energy Transfer (“Sankey”) diagrams Consider a light bulb. Let’s say that the bulb runs on 100 watts (100 joules per second) and transfers 20 joules per second into light and the rest into heat. Draw this as a diagram: 100 J/s electrical energy “Input” energy“Output” energy 80 J/s heat energy (given to the surroundings) 20 J/s light energy

02/09/2015 Example questions Consider a computer: 150 J/s electrical energy 10 J/s wasted sound 20 J/s wasted heat Useful light and sound 1)How much energy is converted into useful energy? 2)What is the computer’s efficiency?

02/09/2015 Reducing Energy Usage How can we reduce energy usage?