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Light Wave or Particle?

# Light Wave or Particle?

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## Light Wave or Particle?

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

2. Evidence Wave Properties Interference of Light Particle Properties

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

9. Diffraction of Light A single point? Or a broken line? 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. If I fire this laser through a small slit, what will I see on the wall when it hits?

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

11. OR IS IT??

12. 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 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 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. 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. The dual nature of light