P7 Flashcards
What are the types of energy stores?
CEMENTGK C- Chemical E- electrostiatic M- magnetic E - elastic potential N- nuclear T- thermal G- Gravitational Potential K - Kinetic
How is energy transferred between stores?
By Heating - energy transfer from hot to cold object
Mechanically - object moving due to force
Electrically - charge moving through a potential difference
Radiation -energy transfer by light and sound waves
What is the law of conservation of energy
Energy cannot be created or destroyed. Energy can only be transferred between stores. The total energy of a closed system has no net charge.
What is the calculation of energy efficiency
Useful Output / Total Input * 100
Josh drops a ball from 200cm and wants it to bounce to a height of 250cm. Explain why this is not possible
It cannot be more than 100% efficient.
Extra energy is needed for this to happen.
What is the equation for work done?
Work done = force * distance
A car rolls down a slope
The energy at the bottom of the slope is lower than expected.
Suggest 2 ways to improve the efficiency.
Reduce friction
Make the shape of the car more streamlined to reduce drag.
Describes what happens to the kinetic energy of the car as it brakes and stops
Kinetic energy is thermally transferred to thermal energy store in brakes and surroundings.
The air holes allow more air to circulate around the discs. Suggest how these brakes can reduce braking distances.
Heat dissipate to air more quickly
Explain how the thermogram can be used to compare how much heat energy is lost from different parts of the house.
Thermogram shows the temperature at different parts of the house. If it turns red on the thermogram it means it needs insulation, heat is being lost. If it turns purple, dark blue it means it is well insulated and heat is not lost.
Allan thunks that some of the energy completely disappears. How could the adviser use the Sankey diagram to explain that this was not scientifically correct.
The wasted energy is shown on the diagram.
The wasted energy and the useful energy add up to produce input energy .
Cars and lorries have different brakes. Brakes absorb energy of the vehicle before it comes to rest. Brakes are designed for increased air flow. Explain why this is more important for lorries than cars.
Lorry has more KE than a car at the same velocity so more absorption of energy by larger brake discs
There is a higher rate of dissipation of energy to surrounding air , therefore brakes are less likely to overheat
Carly has a hair dryer. It has a plastic case and an insulated cable. She attaches a plug into the hair dryer. Explain why the plug only needs two wires and a fuse. Explain why this fuse needs to be 13amp rather than a 3amp.
3A is below normal as current is required by hairdryer.
To check correct fuse you do power = voltage x current
A fuse is needed for safety reasons as if too much current flows, fuse will melt.
Only two wires are needed - earth is not needed as the hair dryer is double insulated and cannot become live.
