Section 4 notes: Energy Resouces and transfer

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b) Energy TransferStudents will be assessed on their ability to:4.2 describe energy transfers involving the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational): a) What energy transfers take place when you turn on a torch?: Chemical-->heat+lightb) Describe the energy transfer that takes place when a fuel is burned in order to cook food=Kientic=Sound(Wasted)+Kientic+Light(useful)4.3 understand that energy is conserveda) A bouncing ball is dropped from a height of 2m, but only bounces to a height of 1m. What has happened to the energy lost in this example? The energy has been conservedb) A swinging pendulum will gradually come to rest. Explain why: Because the pendulum will eventually run out of energy to convert into kientic4.4 know and use the relationship:Efficiency = useful energy output / total energy inputa) The input work you do on a can opener is 24 J. The output work the can opener does is 18 J. What is the efficiency of the can opener? 1.3333...b) A crane moved lifted a concrete block until the block had 104,000J of gravitational potential energy. If the crane used 200,000 J of energy, how efficient was the crane?c) What is the efficiency of a machine when the input is 263 J and the output is 142 J?4.5 describe a variety of everyday and scientific devices and situations, explaining the fate of the input energy in terms of the above relationship, including their representation by Sankey diagrams: 4.6 describe how energy transfer may take place by conduction, convection and radiation:

Conduction: The transfer of thermal energy through a substance without the substance itself moving. The particles have more kientic energy. The more energertic particles transfer some energy to particles near to them. The particles therefore gain energy and then pass energy on to particles near to them. This takes place in all materials. Metals are good conductors of heat because they have free electrons

Convection: Transfer of heat through fluids(liquids and gases) by the upward movement of warmer less dense regions of fluid. This happens because of a convection current. The hot fluid rises until it can't rise no more, goes all the way to the other side where it gets colder, and then sinks.

Radiation:

The transfer of energy by infrared waves. In radiation, heat is travelling in a straight line. Also, Polished, shiny surfaces are good reflectors as well as white surfaces, but matt black and dark surfaces are poor reflectors, or good absorbers.

4.7 explain the role of convection in everyday phenomena:

It can be used in a convection heater. The heater heats cold air at the botom and makes it hotter until it becomes warm.

4.8 explain how insulation is used to reduce energy transfers from buildings and the human body:

For walls, there is a cativity or air gap inbetween the bricks. Glass fibre insulating wool may be placed to stop the convection currents. Also, if the house is older, quick-setting foam can be injected. Double glazing can also be used as two sheets of glass, and to keep the heat inside. To insulate people u can wear thick clothes like gloves.

c) Work and powerStudents will be assessed on their ability to:4.9 know and use the relationship between work, force and distance moved in the direction of the force:Work Done = force x distance movedW = F x d

4.10 understand that work done is equal to energy transferred Yes

4.11 know and use the relationship:Gravitational Potential Energy = mass x g x heightGPE = m x g x h

4.12 know and use the relationship:Kinetic Energy = 1/2 mass x speed2KE = 1/2 m x v2

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work.

Because when E= GPE+KE, so if the GPE increases then KE decrease, and when KE increases GPE decreases

4.14 describe power as the rate of transfer of energy or the rate of doing work

4.15 use the relationship between power, work done (energy transferred) and time taken:Power = work done / time takenP = W / t