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P1.7 Energy and efficiency - Coggle Diagram
P1.7 Energy and efficiency
When you lift an object, energy stored in your muscles is tranferred to the gravitational potential energy store of the object.
The amount transferred depends on weight and height.
Weight = Newtons
1kg = 10N
Energy = Joules
1N x 1m = 1 joule
Units of measurement
Newtons for weight
Energy is measured in joules
How can we calculate efficiency, what limits does it have and how can we improve it
Efficiency
= Useful output energy transferred into device/total input energy supplied to the device (Both measurements in joules J)
Example 1 - light bulb
Radiates 15J of energy as light for every 100J of energy supplied to it.
Efficiency = 15/100 = 0.15
Efficiency = 0.15 x 100 = 15%
GPES = useful energy tranferred
No device can exceed 100% efficiency. Because you can ever get more energy than supplied.
Friction causes heat in moving parts
Lubrication the moving part to reduce friction
The resistance of a wire causes the wire to get hot when a current passes through it
Use wires with as little electrical resistance as possible
Air resistance causes the moving object to waste energy
Steam line the object to reduce air resistance
Input Energy
= energy supplied to the device
Useful output energy
= useful energy transferred by the device
Input energy (J) = useful output energy (J) + energy wasted (J)
Key points
The efficiency of a device = useful energy transferred by the device divided total energy supplied by device (x100)
No energy transfer can be more than 100% efficient.
Machines waste energy because of friction between their moving parts, air resistance, electrical resistance and noise.
Machines are made more efficient by reducing the amount of energy they waste. Example: lubrication.