Temperature and radiation Flashcards
objects and EM radiation
all objects emit EM radiation above absolute zero
their temperature depends on how much of it they absorb and how much of it they radiate
emitting radiation
an object at 90 degrees will emit mostly infared radiation, whereas the Sun’s surface temperature of 5700C means that it emits visible light and ultraviolet radiation
these types of radiation have a shorter wavelength than infared
bodies that are hotter than the Sun will emit X-rays
factors affecting temperature
- a body at a constant temperature absorbs the same amount of radiation as it emits
- an object will increase its temperature if it absorbs more radiation than it emits
- an object will decrease its temperature if it emits more radiation than it absorbs
(as temperature increases, more energetic radiation is emitted)
factors affecting temperature of the Earth
depends on how much radiation is absorbed and emitted
the sun emits radiation
- reflected by atmosphere
- reflected by clouds
- reflected by Earth’s surface
- absorbed by land and oceans
- absorbed by atmosphere
- absorbed by clouds
- radiated from the Earth to space
- absorbed by clouds
- absorbed by the atmosphere
- clouds & atmosphere release more radiation that goes directly to space
intensity and wavelength
intensity is the energy emitted per square metre per second - or the power emitted per square metre
the intensity and wavelength emitted by a body depend on its temperature
a hotter temperature increases the intensity, and the wavelength corresponding to the maximum intensity increases
Explain why the temperature of the Earth also changes over the course of the day [2]
during the day, the side of the Earth facing the sun absorbs more radiation than it emits and so it warms up
the opposite happens at night when facing away from the sun
Describe what you know about a body when its temperature is increasing [2]
the rate at which the body absorbs radiation is greater than the rate at which it emits radiation
Explain the conditions needed for the Earth to remain at a constant temperature [2]
the rates at which the Earth emits and absorbs thermal energy must be equal
Explain why the colour of a star depends on its surface temperature [4]
temperature is related to wavelength
the wavelength of radiation in the visible part of the EM spectrum determines the colour that is seen
so changing the temperature changes the wavelength which changes the colour
What is Leslie’s cube and which practical is it used for?
used to demonstrate how the nature of surface affects the rate at which thermal energy is absorbed or emitted
it can be filled up with hot or cold water and each side observed to find the different rates of radiation or absorption
Explain why the starting temperature for the Leslie’s cube practical needs to be kept constant [4]
the rate at which a body loses thermal energy is directly related to the temperature, so a constant, fixed temperature is needed at the start so that a fair test can be established for comparisons
