Topic 1-Energy Flashcards
(39 cards)
Energy stores: •kinetic energy •chemical energy •internal/thermal energy •gravitational potential energy •magnetic energy •electrostatic energy •elastic potential energy •nuclear energy
Energy is measured in joules
There is always the same amount of energy at the start as there is at the end
The principle of conservation of energy
This states that the amount of energy always stays the same. There are various stores of energy. In any process energy can be transferred from one store to another, but energy cannot be destroyed or created
Light, sound and electricity are not stores of energy.
They are ways of transferring energy from one store to another.
EG: In a torch the chemical energy stored in a battery causes an electric current, the electric current causes the temperature of the bulb to increase so it lights up. The light cannote be stored
To calculate kinetic energy:
Kinetic energy=1/2 x mass x (speed)2
Ek=1/2mv squared
To calculate elastic potential energy:
Elastic potenial energy=1/2 x spring constant x (extension)2
Ee=1/2ke squared
To calculate gravitational potential energy:
Gravitational potential energy=mass x gravitational field strength x height
Ep=mgh
Work:
A force does work on an object when the force causes the object to move in the direction of the force
To calculate work:
Work=force x distance
W=fs
When we do work, by applying a force to an object, we change the energy store of that object
EG: When 200J of work is done to lift a box up, the gravitational potential energy store of the box increases by 200J.
EG: When 2J of work is done to stretch a spring, the spring stores 2J of elastic potential energy
Power is defined as the rate at which energy is transferred or the rate at which work is done.
To calculate power:
Power=energy transferred
Time
P=E/T
Power=work done
Time
P=W/T
To calculate the amount of energy stored or released from a system, as its temperature changes:
Change in thermal energy=mass x specific heat capacity x temperature change
∆E=mc∆
The specific heat capacity:
The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg of the substance by 1 degree
Required Practical 1:
Measuring the specific heat capacity of a material
Energy is transferred from an electrical immersion heater to a metal block. The increase in temperature of the metal block depends on the mass and spec heat capacity of the block
- Measure the mass of the metal block
- Put thermometer and heater in the holes in the block
- Connect heater, joulemeter and power supply
- Measure temp of metal block and switch on power supply
Required Practical 1 continued:
- When the temp of the block has gone up by 10 then turn power supply off and write reading. This is the amount of energy transferred to the immersion heater.
- Keep the heater in, keep looking at the temperature and write down the hightest one on the thermometer
Dissipation of energy:
Often, when energy is transferred some of the energy is dissipated or ‘wasted’
To dissipate means to scatter in all directions or to use wastefully. When energy has been dissipated, it means we cannot get it back. The energy has spread out and heats up the surroundings
Reducing energy dissipation: Power stations
The purpose of a power station is to generate electricity. Engineers desing generators to reduce the amount of waste energy. Generators are large machines which can dissipate energy by heating or by unwanted mechanical vibrations.
Reducing energy dissipation: car design
Engineers design fuel efficient cars which dissipate less energy.
The car is made streamlined to reduce air resistance on the car.
Moving parts of the car are lubricated with oil to reduce friction.
Reducing energy dissipation: keeping warm at home
•Chimneys
Some of the energy from burning coal is transferred to the air outside the house, this is wasted energy. By having the chimney inside the house, thermal energy can be transferred into the bedrooms upstairs, this is useful energy.
Reducing energy dissipation: keeping warm at home
•Walls
The rate at which energy is transferred through walls depends on:
- temperature difference between inside and outside
- the area of the walls
- the thermal conductivity of the walls
- the thickness of the walls or windows, thicker walls=slower energy loss
Reducing energy dissipation: keeping warm at home
•Walls-continued
Modern houses are built with 2 layers of brick. Then the house is insulated with cavity wall insulation between the brick. The foam which insulates is full of trapped air, air is a good inusulator as is has a much lower thermal conductivity than brick or glass.
Reducing energy dissipation: keeping warm at home
•Loft insulation and carpets
A thick layer of loft insulation reduces energy loss through the roof. We also use insulating carpets to reduce energy loss through the floor.
Reducing energy dissipation: keeping warm at home
•Double glazing
A thin pane of glass in a window transfers energy out of the house. We use double glazing to reduce energy loss through the windows. A layer of gas trapped between two panes of glass provides good insulation
Required Practical 2: Investigating thermal insulation
- Select materials for insulators
- Wrap one around a glass beaker
- Pour hot water in
- Put a card lid on and put a thermometer in
- Take start temperature and start stop clock.
- Wait 10 mins then take temp again
- Calculate fall in temperature
- Repeat for each material
Control variables:
A control variable is what you keep the same
Categoric Variable:
A categoric variable has values that are given a name or label
