Question

• Describe The problem: Ultraviolet Catastrophe

E = h f

E = n h f

H = Planck’s constant = 6.62 x 10-34 Joule – Second

   Quantum    singular

   Quanta        plural

*   Describe the Stephan - Boltzmann Law P/A = Sigma T4

* Describe Wien's Law Wavelength = A constant/ T (K) The color of an object only depends on its temperature

*   Describe the Photoelectric Effect

*   De Broglie mathematical expression for particle waves - Wavelength x Momentum = Planck's Constant

Answer 1

1 ) Blackbody is an object which absorbs and emits all frequencies. Classical physics gives relationship between intensity of blackbody radiation and frequency for a fixed temperature, the result works well for low frequency region and is known as Rayleigh-Jeans law. But it's result diverges at high frequency , Since it is in UV region so this divergence for high frequencies is called the ultraviolet catastrophe.

Max Plank explained this by assuming that energy of oscillation of electron must be integral multiple of hv.

E = nhv

h is plank constant

v is frequency of oscillation.

2) Stefan Boltzmann law states that the total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature.

E is the radiant heat energy emitted from a unit area in one second (that is, the power from a unit area) and T is the absolute temperature (in kelvins), then

E = σT4

3) Wien's Law tells us that objects of different temperature emit spectra that peak at different wavelengths. This law gives the relationship between the temperature of a blackbody and the wavelength at which it emits the most light. He found that λm*T is an absolute constant:

λmT = 0.2898 centimetre-degree Kelvin

Since wavelength is associated with colour and it only depends on temperature so colour of an object will also only depend upon temperature.

Photoelectric Effect: When photons (light waves) emitted from source are incident on metal surface then the electrons are emitted from it.

The energy of emitted electron E = hv - W

hv = Energy of incident photons

W = work function of material ( metal surface)

So energy of incident photon must be greater than the work function of material for photoelectric effect to take place.