Presentation on theme: "REMEMBER: Energy cannot be created or destroyed – This is the Law of Conservation of Energy. Energy can be transformed from one form to another or transferred."— Presentation transcript:
REMEMBER: Energy cannot be created or destroyed – This is the Law of Conservation of Energy. Energy can be transformed from one form to another or transferred from one place to another. Surfaces & radiation Dark matt surfaces are better emitters of thermal radiation than light shiny surfaces. Dark matt surfaces are better absorbers of thermal radiation than light shiny surfaces. Incident radiation On a smooth surface light is reflected and absorbed. Types of energy: Chemical e.g. batteries, food Kinetic e.g. moving object Gravitational potential e.g. due to its position. Elastic (strain) e.g. in springy object when we stretch or squash it. Electrical e.g. transfer by an electric current. Thermal (heat).e.g. burning an object Conduction In a metal is due mainly to free electrons transferring energy inside the metal.e.g. copper. Non-metals are poor conductors as they contain no free electrons. E.g. plastic Convection This only takes place only in liquids and gases (fluids). Heating a liquid or a gas makes it less dense. Convection is due to a hot liquid or gas rising. Incident radiation On a rough surface the light is scattered and then absorbed. Thermal Radiation is energy transfer by electromagnetic waves. All object emit thermal radiation. The hotter an object is, the more thermal radiation it emits. Thermal scanning are used in hospitals to detect tumours under the skin. Also temperature strips are used in industry and food packaging. P1a, Physics Heat transfer by design Radiators have a large surface are so it can lose heat easily. Small objects lose heat more easily. Heat loss can be reduced by: Aluminium foil behind radiators, cavity wall insulation, double glazing, loft insulation, vacuum flask Useful energy is the energy transferred to where it is wanted in the form it is wanted. E.g. a light bulb to provide light. Wasted energy is the energy that is not usefully transferred or transformed. E.g. a light bulb also makes heat. Energy & Efficiency Energy is measured in Joules. The efficiency of a device = USEFUL ENERGY TRANSFERRED BY DEVICE TOTAL ENERGY SUPPLIED BY DEVICE
Electrical power The unit of power is the watt (W), equal to 1 J/s. 1 Kilowatt (kW)=1000 watts. Power (in watts) = Energy transferred (in Joules) Time taken (in seconds) P1a Physics Using electrical energy Formula to work out the amount of electrical energy used: Energy transferred= power of device x time in use (kilowatt hours) (kilowatts) (hours) kWh kW h Total cost = number of kWh used x cost per kWh Sankey diagram Electrical devices Electrical energy is energy transfer due to an electric current. Uses of electrical devices include: heating, lighting, making objects move (use an electric motor) and creating sound and visual images. The National Grid The grid is a network of cables and transformers. We use step-up transformers to step up power stations’ voltages to the grid voltage, Step-down transformers to step the grid voltage down for use in our homes. A high grid voltage reduces energy loss and makes the system more efficient. In the UK 230 volts is for use in homes. Fuel for electricity Electricity generators in power stations are driven by turbines. Much more energy is released per kilogram from uranium than from fossil fuel. Radioactive waste stays around for thousands of years so this is a disadvantage for using uranium. Energy from wind & water A wind turbine is an electricity generator on top of a tall tower. A wave generator is a floating generator turned by the waves. Hydroelectricity generators are turned by water running downhill, mainly used in mountainous areas. A tidal power station traps each high tide and uses it to turn generators. Solar energy and the Earth We convert solar energy from the sun into electricity using solar cells or use it to heat water directly in solar heating panels. Geothermal energy comes from the energy released by radioactive substances deep inside the Earth.