P2-thermal Radiation Flashcards
What is specific heat capacity
Specific heat capacity is the amount of energy needed to increase the temperature of a 1kg block by 1 degree
What is the equation for specific heat capacity
Specific heat capacity = energy (j) divided by mass (kg) x temp change (degrees)
Or power(W) x time(m) divided by Mass (kg) x temp change (degrees)
What is a method for a practical you can do to work out specific heat capacity
- Place an immersion heater into the central hole at the top of the 1kg block
- Place a thermometer into the other smaller hole and add a couple of drops of oil so it is surrounded by hot material
- Fully insulate the block with cotton wool
- Record the starting temperature of the block
- Connect the heater to a power supply ( measure the power going in using an ammeter and a voltmeter )
- Leave the heater on for 10 minutes and record the highest temperature during this time
What happens to the infrared radiation in a hot object as it cools down
As a hot object cools down it emits more IR radiation than it absorbs which decreases its temperature
What happens to the IR radiation in a cold object as it warms up
When a cold object heats up it absorbs more IR radiation than it emits which causes it to get warmer
What is happening to IR radiation in an object that is at a constant temperature
An object at a constant temperature is emmiting IR radiation at the same rate that it is absorbing it
What types of surfaces are best for absorbing and emmiting radiation
Black surfaces are good as well as matte surfaces
Which surfaces are worst for absorbing and emiting IR radiation
White shiny surfaces are worst for absorbing and emmiting radiation
What is a perfect black body
A perfect black body is an object that absorbs all radiation that hits it. It is the best possible emmiter and absorber of IR radiation and it does not reflect or transmit any radiation
How can you measure the IR radiation emitted by different surfaces
You can measure the IR radiation emmited by different surfaces by filling a Leslie cube ( a cube with four different surfaces :matte,black,shiny,white)with boiling water. Then leaving it for 5 minutes before using the IR reader to measure how much radiation each surface has emmited.
How does conduction happen
Conduction happens when an object is heated. By heating the object, energy is transferred to the kinetic energy store if the particles in the object.This causes the particles to vibrate. The particles then collide with other particles around them when vibrating and transfer energy to their kinetic energy stores . This happens throughout the object until energy is transferred to the thermal energy store of the surroundings at the end of the object
What is thermal conductivity
Thermal conductivity is a measure of how quickly energy is transferred through particles through conduction. Objects with high thermal conductivity are able to transfer energy between particles quickly
What is a good insulator
A good thermal insulator is an object that is not dense because the particles dont collide frequently and transfer kinetic energy between themselves. An example of a good thermal insulator is air .
- Good thermal conductors arent good insulators
- The aim of insulators is to conserve energy
What is the method for a practical to measure a good insulator
- Boil water in a kettle. Pour some of this water into a sealable container(wrapped in the material you want to measure the insulating properties of) and measure the mass of the water
- Use a thermometer to measure the initial temperature of the water
- Seal the container and time 5 minutes on a stopwatch
- Measure the final temperature of the water
- Repeat the experiment using a different material to wrap the container with.Make sure to keep the same initial temperature of the water and to keep the same mass
- The lower the temperature difference the better the insulator
What is convection
Convection is the process of heating a fluid . A region of the liquid or gas is heated , the particles move faster and the space between individual particles increases. This decreases the density of the fluid . The less dense heated region then rises over the more dense,cooler region