P1 Revision 4

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• Created by: LBC0502
• Created on: 14-06-14 12:45
• P1 Revision
• Energy
• Useful energy: Energy that is transferred to where it is wanted in the form that is wanted.
• E.g. A person diving: all gravitational potential, some gravitational potential, mainly gravitational potential and some kinetic energy, mainly kinetic energy.
• Wasted energy: Energy this is not usefully transferred/transformed e.g. a light bulb has wasted energy (thermal).
• Conservation of energy: Energy cannot be made or destroyed, it just changes form (transfers energy).
• Sankey diagrams show: total input energy, useful output energy and wasted output energy.
• The eight forms of energy can be divided into two main groups: Can be stored: potential (stored energy), gravitational potential (the energy the object has from its position or place) or stored in springs and rubber bands (elastic) in the bonds between atoms in fuels and food (chemical) in the nucleus of the atom (nuclear). Cannot be stored: kinetic (the movement of waves, atoms and electrons), electrical (the movement of electrions), thermal (the movement of particles within a substance), light and sound (as movement of waves
• Specific Heat Capacity
• Denser materials heta up quickly e.g. water - 4200J/Kg ?, copper 380J/Kg ?. Oxygen would have a higher specific heat capacity because the particles are further apart.
• Specific heat capacity is unique to each material (solids, liquids and gases). Specific heat capacity is the amount of energy required to raise the temperature of 1kg by 1?.
• Calculate the energy required to raise the temperature of 12kg al aluminium from 15? to 35?:- E = mc?. E = ?. m = 12kg. T1 = 15?. T2 = 35?. c = 880J/Kg ?.- ? = 35-15 = 20?. E = 12 x 880 x 20 = 211,200J
• E = mc?. E = Energy (J), m = Mass (kg), c = Specific Heat Capacity (J/Kg ?), ? = Change in temperatures (?) (Formula Triangle)
• Efficiency
• Efficiency = Useful energy/power transferred ÷ Total energy/power supplied (input). Efficiency as a decimal of percentage.
• Energy supplied = Useful energy delivered + Wasted energy delivered.
• An electric motor is used to raise an object. The object gains 60J of gravitational potential energy when the motor is supplied with 200J of electrical energy. Calculate the efficiency of the motor:- Efficiency = Useful energy supplied ÷ Total energy supplied.- Efficiency = 60J ÷ 200J = 0.3 or 30%
• An efficient appliance is one that wastes a small amount of energy. This reduces the cost of operating the appliance.
• Uses of Specific Heat Capacity
• Low specific heat capacity: Doesn't take lots of energy to get hot. Doesn't stay hot for long.
• Heaters filled with oil have a high specific heat capacity because oil is good at storing energy and would keep heat energy for a long time. It also takes a lot of energy to get hot. This can transfer a lot of energy to the room.
• High specific heat capacity: Takes lots of energy to get hot, stays hot for a long time. Good at storing energy.
• Storage Heaters: The heater contains concrete or bricks which has a high specific heat capacity because the concrete/bricks takes a lot of energy to heat up. Also, the concrete/bricks are good at storing thermal energy. The storage heater will stay hot for a long time and the storage heater will transfer thermal energy to the room (same concept for water).
• Saucepans: The saucepan should have a LSHC to transfer thermal energy to the food to heat it up quickly. Thermal energy doesn't need to be stored. The saucepan handle should have a HSHC, it will heat up slowly and take a lot of energy to heat up. (Wooden spoon = HSHC, oven gloves = HSHC)