wrxsti said:
1) Discuss Evidence for the Particle Nature of Light.
2) Dicuss Evidence for the ability of the WAVE model of light to explain the photoelectric effect
Could someone explain these in a lot of detail cause im having trouble with this
1)
Because the classical wave theory cannot explain why the energy on the Black-Body radiation curve increased without limit at greater frequencies, the particle theory introduced in the form of quantum physics was used to explain this.
Experimental evidence was used to explain the particle nature of light.
The evidence of the particle nature of light is just the experimental results of the photoelectric effect experiment.
When light of a high frequency was shone on a metallic surface it was seen that a current was detected from the liberation of photoelectrons.
The experiment also showed that photoelectrons were only released at certain frequencies which was related to the work function of a metal.
This did not support the claim that emission was independent of the frequency.
Initially it was thought that as the intensity of light increased so did the kinetic energy, however the experiment showed that the maximum kinetic energy of the electrons remained constant regardless of the intensity.
Why? Because the energy of light was in packets (quanta) so whether there is 1 or 1,000,000 photons striking a metallic surface, that 1 or the 1,000,000 electrons will all receive the same energy to lift off a surface (provided hf > Φ) , because the light energy that traveled in packets all carried the same amount of energy.
So the maximum kinetic energy of the photoelectrons did NOT depend on the intensity of the light.
This showed that light transferred either all of its energy or none of it (1 or 0, nothing in between, less or more).
In short, experimental results of the particle theory were different from the classical predictions proposed for the wave theory.
2)
When you increase the intensity of a light source, according to the particle theory, more photoelectrons will be liberated off a surface.
But, since light has a dual wave-particle nature, the wave model can also be used in conjunction to explain the photoelectric effect.
In the wave theory, the intensity of a light source is represented by the amplitude of a light wave, so in the particle-theory a high-intensity light source will result in more photoelectrons being liberated and detected as current.
Picture this,
Pretend that the function of a wave of light is represented by y = sin x
If you double the intensity you get y = 2 sin x, the amplitude is twice the one before, meaning twice the intensity (wave) and twice the amount of photons (particle) striking a fixed area.
If you decide to increase the intensity of light (wave) you will increase the amount of photons (particle) striking a fixed area by 9 times more, you will get 9 times as much photoelectrons being liberated.
The wave theory contributes to our understanding of the particle nature of light but is somewhat severely limited hence the introduction of Planck's quantum physics.
So you see that the Preliminary course looks at the wave nature of light, whereas the HSC course focuses on the particle nature of light.
That's a lot to write in the exam unless it's going to be an 8-marker.
