| Black bodies & the Opposite | BLACK BODIES:
- No object is perfect at absorbing/emitting all the radiation, objects close to this are called: black bodies (eg, stars)
- A perfect black body: would absorb all radiation that falls onto it, wouldn't reflect/transmit any radiation
- A good absorber is also a good emitter
POOR ABSORBERS & EMITTERS:
- white & shiny silvery surfaces (worst absorbers as they also reflect all visible light wavelengths)
- Radiators are usually painted white as they emit IR slowly and gradually |
| PRACTICAL: How the amount of IR Radiation Absorbed/Radiated Depends on the Nature of the Surface (3 Stages) | 1) Place a Leslie cube on a heat-resistant mat. Fill it, almost to the top, with boiling water and replace the lid.
2) Leave for one minute, so that the surfaces heat up to the temperature of the water.
3) Use the infrared detector to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface. Make sure that the detector is the same distance from each surface for each reading
Notice: Matt objects will reflect the most IR, black objects will reflect the most IR |
| What does Earths Temperature depend on (4 Factors)? | 1- the rate at which light & IR radiation is absorbed & emitted by earths surface and atmosphere
2- greenhouse gases ∴ activities like deforestation can increase temp. leading to climate change
3- When light & high frequency IR radiation is absorbed by Earth's surface, it's internal energy increases and it becomes hotter, some of this energy is transferred to the atmosphere by conduction and convection.
4- Low frequency radiation either bounces back into space or is absorbed by GHGases |
| What happens as the temperature of a body(object) increases | (All objects emit IR)The hotter the body(object):
- the more infrared it gives out at a time
- the greater the proportion of emitted radiation as visible light |
