1. Both We call this the “Dual Nature of Light”
Light Wave or Particle?
Both
We call this the “Dual Nature of Light”

2. Evidence
Wave Properties
Interference of Light
Particle Properties

3. When two light waves hit they pass through each other.
Interference of Light
When two light waves hit they pass through each other.
While they occupy the same space the waves combine amplitudes and frequencies to produce a different wave. This is called interference.
If two particles hit they bounce off each other. They don’t interfere like waves.

4. Refraction & Dispersion
Evidence
Wave Properties
Interference
Refraction & Dispersion
Particle Properties

5. Refraction & Dispersion of Light
When light enters glass it bends.
This is called refraction
How much light refracts depends on the type of glass and the color of light.
A particle could refract, wave theory works better.
When white light enters glass the different frequencies bend differently.
This causes the light to split into the rainbow.
This is called dispersion.
Particles wouldn’t display dispersion.

6. Refraction & Dispersion
Evidence
Wave Properties
Interference
Refraction & Dispersion
The Doppler Effect
Particle Properties

7. The Doppler Effect for Light
When a light source is moving the frequency of light it emits changes due to this motion.
A particle doesn’t do this, only a wave.

8. Refraction & Dispersion
Evidence
Wave Properties
Interference
Refraction & Dispersion
The Doppler Effect
Diffraction
Particle Properties

9. Diffraction of Light
You get a broken line, called a diffraction pattern.
Basically the light bends as it passes through the slit causing an alternating series of constructive and destructive interference.
A particle wouldn’t do this.
A single point?
Or a broken line?
If I fire this laser through a small slit, what will I see on the wall when it hits?

10. Refraction & Dispersion
Evidence
Wave Properties
Interference
Refraction & Dispersion
The Doppler Effect
Diffraction
SO… Light is a Wave!!!!!!!!!!!!
Particle Properties

11. OR IS
IT??

12. Refraction & Dispersion The Photoelectric Effect
Evidence
Wave Properties
Interference
Refraction & Dispersion
The Doppler Effect
Diffraction
SO… Light is a Wave!!!!!!!!!!!!
Particle Properties
The Photoelectric Effect

13. The Photoelectric Effect
When light hits certain metals it causes the metal to eject electrons.
Treating light as a wave tells us that the brighter the light, the more electrons get ejected or the electrons get ejected at a faster speed.
This would be true if it wasn’t false!!!
It turns out the frequency of the light is what determines whether or not electrons are ejected from the metal.
This suggests that light travels in quanta or packets called photons which behave like particles.

14. Evidence SO… Light is a Wave!!!!!!!!!!!! Wave Properties
Interference
Refraction & Dispersion
The Doppler Effect
Diffraction
SO… Light is a Wave!!!!!!!!!!!!
Particle Properties
The Photoelectric Effect
The Ultraviolet Catastrophe

15. The Ultraviolet Catastrophe
A blackbody radiator absorbs all electromagnetic radiation that hits it and emits its own electromagnetic radiation based on its temperature.
Wave theories predict that the wavelengths of electromagnetic waves a blackbody will emit should follow the relationship shown by the dashed curve in the graph.
It turns out that experiments show that the wavelength of electromagnetic waves emitted by a blackbody actually follow the solid curves shown in the graph called blackbody curves.
Which curve is determined by the temperature of the blackbody.

16. Our Sun’s Blackbody Curve

17. The Ultraviolet Catastrophe
This also suggests that light travels in quanta or packets called photons which behave like particles.

18. ???????????????????? Evidence SO… Light is a Particle!!!!!!!!!!!!
Wave Properties
Interference
Refraction & Dispersion
The Doppler Effect
Diffraction
SO… Light is a Wave!!!!!!!!!!!!
Particle Properties
The Photoelectric Effect
The Ultraviolet Catastrophe
SO… Light is a Particle!!!!!!!!!!!!
????????????????????

19. The dual nature of light
Light is a wave
Light is also a particle
Light travels in packets of waves called photons.
These photons act like particles and waves depending on what is being observed.
The energy of each of these photons depends on the frequency of the contained wave.