Page 22 - Spotlight A+ Physics Form 4.5

Form
5 Physics Chapter 7 Quantum Physics

7.1 Quantum Theory of Light
1. The electromagnet spectrum is a continuous spectrum that consists of seven types of waves with different
frequencies and wavelengths.
2. Figure 7.1 shows seven types of waves with their frequencies and wavelengths.

Increasing wavelength
Wavelength / m
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10 –11 10 –10 10 –9 10 –8 10 –7 10 –6 10 –5 10 –4 10 –3 10 –2 10 –1 1 10 1 10 2 10 3 10 4
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Gamma X-rays Ultraviolet Infrared Microwave Radio waves
rays radiation radiation

10 20 10 19 10 18 10 17 10 16 10 15 10 14 10 13 10 12 10 11 10 10 10 9 10 8 10 7 10 6 10 5 10 4 Frequency / Hz
Increasing frequency
Visible light

400 500 600 700 750
Wavelength / nm
Figure 7.1
3. Any object with a temperature above absolute
zero emits electromagnetic radiation at all
wavelengths. The usual meaning of 'black' is absorbs visible light.
4. Objects with low temperature or cold objects But in Physics, a black body is one of that absorbs
emit waves with low frequencies such as radio all the radiation that falls on it, at all wavelengths.
waves or microwaves. It is the perfect absorber and radiator. Our Sun is a
5. Meanwhile, objects with high temperature or back body.
hot objects emit waves with high frequencies
such as visible light and ultraviolet radiation. 8. The emitted radiaton forms a continuous
6. A black body is an idealised body that is able to spectrum and is unaffected by the nature of the
absorb all electromagnetic radiation that falls black body surface.
on it.
9. When the temperature of an object rises, the
object (black body radiator) emits thermal
radiation at all wavelengths.
Simulation of black body
spectrum
https://bit.ly/35FlCtc
The light rays that
7. A black body also emit thermal radiation enter the ear cavity
depending on its temperature and is known as will undergo repeated
black body radiator. reflections on the inner Ear
walls of the ear cavity. cavity
At each reflection,
parts of the rays are
absorbed by the inner
CHAP Thermal radiation is electromagnetic radiation walls of the ear until all the rays are absorbed. Thus,
7 consist of visible light and radiation that cannot be the ear cavity acts like a black body.
seen by the human eye such as infrared radiation.

472 7.1.1