Optical Phenomena & Properties of Matter
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OPTICAL PHENOMENA AND PROPERTIES OF MATERIALS 1. a) Explain the term the photoelectric effect. b) In what three forms do we find the photoelectric ef fect, and give a short description of each. 2. When light with a wavel ength of 300 nm falls on the surface of sodium, electrons with a kinetic energy of 1,68 x 10 5 J are emitted. What is the minimum energy needed to remove an electron from sodium? 3. When light hits an object it will display a certain behaviour. Name three things that determine the behaviour of light. 4. Explain the fol lowing t erms and use diagrams to illustrate your answer: a) Tr ansmission of li ght b) Absorpti on of li ght c) Reflecti on of li ght. 5. a) What does LASER stand for? b) How do lasers work? c) Name two applications of lasers in our modern world.
Transcript of Optical Phenomena & Properties of Matter
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OPTICAL PHENOMENA AND PROPERTIES OFMATERIALS
1. a) Explain the term the photoelectric effect.
b) In what three forms do we find the photoelectric effect, and give a
short description of each.
2. When light with a wavelength of 300 nm falls on the surface of
sodium, electrons with a kinetic energy of 1,68 x 105 J are emitted.
What is the minimum energy needed to remove an electron from
sodium?
3. When light hits an object it will display a certain behaviour. Name
three things that determine the behaviour of light.
4. Explain the following terms and use diagrams to illustrate your
answer:
a) Transmission of light
b) Absorption of light
c) Reflection of light.
5. a) What does LASER stand for?
b) How do lasers work?
c) Name two applications of lasers in our modern world.
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SOLUTIONS
1. a) The photoelectric effect is the emission of electrons from thesurface of a metal when light, with a frequency above thethreshold frequency of the metal, is radiated (shone) on the
metal.
b) i) the photo-emissive effect - electrons are released into free
space adjacent to the surface of the metal.
ii) the photoconductive effect - it occurs when there is a
marked change in the conductivity of a material that is being
irradiated.
iii) the photovoltaic effect – the process whereby light energy is
directly converted into electrical energy.
2. The energy of a 300 nm photon is given by:
W = hf o = hc = 6,63 x 10-34 3,0 x 108
λ 300 x 10-9 1
= 6,63 x 10-19 J
3. a) The energy of the light striking the object.b) The vibration frequency of the electrons in the object.c) How strongly the atoms in the object hold on to their electrons.
4. a) Transmission of light describes the situation in which light passesthrough a substance virtually unchanged.
Incoming light
Transmitted light
b) Absorption of light occurs when the light striking a surface is
neither transmitted nor reflected, but rather absorbed by thematerial and the electrons use the energy and start to vibratemore energetically.
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Incoming light
Absorbed light
c) Reflection of light occurs when light beams hit the surface of certain materials and do not penetrate into the material but rather ‘bounce’ off.
Incoming light Reflected light
5. a) LASER stands for Light Amplification by Stimulated Emission of
Radiation.
b) Lasers work by selecting light in a particular wavelength,organizing it and making it directional, rather than releasing it inmany different directions. This is achieved by stimulatedemission, which results in many photons of the same energy beingreleased at the same time in the same direction.
c) Lasers can perform delicate surgery such as eye surgery.Lasers have also allowed for the development of the CD becausethey can store and read information.Supermarket scanners usually have helium-neon lasers to scanthe universal barcodes to identify products.The Laser printer has recently become the main instrument for printing in offices.
