Energy Flashcards
What does efficiency mean
Efficiency is a measure of how good a device is at changing energy from one form to another
What does power mean
Power is the amount of energy transferred by a device in one second
Conservation of energy
Energy in = energy out
What is an independent variable
The thing you change
Dependent variable
The variable you measure or test
Control variable
Variable you keep the same
What is a closed system
A system where it’s components only interact with itself not the outside world. No energy is exchanged outside the system.
What is an open system
A system where it’s components and energy are exchanged with the things outside the system
What are the ways heat can travel
Conduction
Convection
Radiation
What is conduction
The measure of heat transfer in solids but not liquids and gases
How does conduction work
Energy is passed along the particles of the solid. The particles gain more energy, vibrate more vigorously and collide with neighbours. The free electrons gain kinetic energy when a metal is heated.
What does insulate mean
To block from electricity or heat and reduce the amount of energy transfer across a material
What is specific heat capacity
The amount of energy needed to change the temperature of 1kg of the substance by 1•c
The amount of energy to heat a substance up depends on
- mass of substance
- the substance itself
- the temperate change
What does the rate of energy transfer across a material depend on?
the temperature difference across a material
the thickness of the material
The thermal conductivity of the material
What is ideal properties of thermal insulation?
Have as low thermal conductivity as possible
Be as thick as practically possible
What is payback time?
How long it takes for the cost of installing insulation to be equalled by the savings from reduced energy costs
What is heat
The amount of of thermal energy stored in an object or substance
Amount of heat out =
Amount of heat in - it’s thermal equilibrium where it matches it’s surroundings
What is infrared radiation?
A type of electromagnetic wave which transfers heat energy
What is emitted from objects as infrared radiation?
Thermal heat energy
Matte black is …
The best emitter of infrared radiation and the best absorber
Silver shiny is …
The worst emitter and absorber of infrared radiation but the best reflectors
What is a black body emitter?
An object that absorbs all radiation that hits it and does not reflect any
