Thermal Radiation (Edexcel GCSE Physics): Flashcards
Exam code: 1PH0
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Define thermal radiation.
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Define thermal radiation.
Thermal radiation is a spectrum of electromagnetic waves emitted by all bodies, regardless of temperature, usually in the infrared region of the spectrum.
How does an object's temperature affect the amount of infrared radiation it emits?
The hotter the object, the more infrared radiation it radiates in a given time.
How does increasing temperature affect the peak of a thermal radiation curve?
The peak moves to a lower wavelength and a higher intensity.
At around 1000 °C, an object will emit a significant amount of ______ light, while at 6000 °C it will mainly emit white or blue light.
At around 1000 °C, an object will emit a significant amount of red light, while at 6000 °C it will mainly emit white or blue light.
Define thermal equilibrium.
Thermal equilibrium is reached when an object absorbs radiation at the same rate as it emits radiation, so its temperature stays constant.
True or False?
An object's temperature increases when it absorbs radiation faster than it emits radiation.
True.
The temperature of a body increases when it absorbs radiation faster than it emits it, and it cools down if it emits radiation faster than it absorbs it.
Why do rescue teams use light-coloured, shiny emergency blankets to keep accident survivors warm?
A light, shiny surface emits less radiation than a dark, matt surface, so less infrared radiation is lost from the patient, keeping them warm.
Define the greenhouse effect.
The greenhouse effect is the natural process by which greenhouse gases absorb and re-radiate infrared radiation emitted by the Earth, warming the Earth's surface.
Name three greenhouse gases that absorb infrared radiation emitted by the Earth.
Water vapour, methane and carbon dioxide.
Why would the Earth's surface temperature drop to about −180 °C at night if it had no atmosphere?
Without an atmosphere, the surface would emit all the radiation it receives from the Sun straight into space, with none retained by greenhouse gases.
What three processes determine the Earth's temperature, in terms of radiation from the Sun?
Light and infrared radiation from the Sun are reflected back into space, absorbed by the Earth's atmosphere or surface, and emitted from the Earth's surface and atmosphere into space.
The Earth emits its own thermal radiation with a ______ wavelength than the radiation it receives from the Sun.
The Earth emits its own thermal radiation with a longer wavelength than the radiation it receives from the Sun.
True or False?
Greenhouse gases absorb longer-wavelength infrared radiation from the Earth and emit it back to the surface.
True.
Greenhouse gases absorb this radiation and then emit it back to the Earth's surface, making the Earth warmer than it would otherwise be.
What is the aim of the Core Practical: Investigating Thermal Energy?
To investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.
What is the independent variable in the Core Practical: Investigating Thermal Energy?
The colour of the flask's surface.
What is the dependent variable in the Core Practical: Investigating Thermal Energy?
Temperature.
Name three control variables in the Core Practical: Investigating Thermal Energy.
Identical flasks (except colour), the same amount of hot water, the same starting temperature of the water and the same time interval.
In the Core Practical: Investigating Thermal Energy, four identical flasks are painted ______, ______, white and silver.
The four identical flasks are painted black, grey, white and silver.
In the Core Practical: Investigating Thermal Energy, why must any difference in heat loss between the four flasks be due to infrared radiation?
Because conduction and convection losses are the same for each flask (identical except colour), so any difference in heat loss must be due to infrared (thermal) radiation.
True or False?
In the Core Practical: Investigating Thermal Energy, most of the heat lost from the beakers is due to infrared radiation.
False.
Most heat lost is due to conduction and convection; only the difference in heat loss between the flasks is due to infrared radiation.
In the Core Practical: Investigating Thermal Energy, how can parallax error be avoided when reading the thermometer?
Parallax error can be avoided by reading the thermometer at eye level.
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