CHEM101 Lecture Notes - Lecture 1: Black Body, Refraction, Diffraction
25 Jun 2018
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Wave property variables:
1. Frequency: cycles per second (n)
2. Wave Length: the distance a wave travels in one cycle (l)
3. Amplitude: the height of a wave crest or the depth of a trough (the intensity / brightness of light is related to its
amplitude)
* wavelength and frequency = reciprocal relationship
Waves and Matter have different behaviours:
1. Refraction:
a. WAVE: When a wave of light enters a new medium, it causes a change of speed which causes a change
in direction known as refraction. (The angle of the refraction depends on the two media being passed
through and the wavelength of the light)
b. MATTER: matter will not refract, for example, if you throw a pebble into a pond it will continue to slow
down gradually along a curved path after it enters the water
2. Dispersion: white light separates /disperses into its component colours when it passes through a prism or
another refracting object because each incoming wave is refracted at a slightly different angle
3. Diffraction: When a wave strikes the edge of an object, it bends around it.
a. EX. if waves pass through a slit, it bends around both edges of the slit and form a semicircular wave on
the other side of the opening. When you throw matter, for example, sand at a small opening, some
particles will hit the edge while others go through the opening and continue in a narrower group.
4. Interference: when wave lights pass through two adjacent slits the nearby emerging circular waves interact
through the process of interference. Two different kind:
a. Constructive: If the crests of the waves coincide, (in phase) The amplitudes add together to form a
brighter region.
b. Destructively: If the crest coincides with the troughs, (out of phase), the amplitudes cancel to form a
darker region. The result is a diffraction pattern.
THE PHOTOELECTRIC EFFECT:
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Document Summary
Ex. if waves pass through a slit, it bends around both edges of the slit and form a semicircular wave on the other side of the opening. When you throw matter, for example, sand at a small opening, some particles will hit the edge while others go through the opening and continue in a narrower group. Interference: when wave lights pass through two adjacent slits the nearby emerging circular waves interact through the process of interference. A monochromatic light shines on a metal surface, electrons are released from the surface of the metal and travel to the electrode, as a result, a current is produced. Observation 1: the effect only occurs above a min. threshold frequency. Observation 2: there is no time lag. Albert einstein"s photon theory: light is a particle and is quantized into small packets of energy called photons.
