Wave-Particle Duality Flashcards
Describe Newton’s corpuscular theory of light.
Newton thought that the light was made up of tiny particles he referred to as corpuscles.
This theory was based on his laws of motion that all particles naturally travel in straight lines.
Reflection - the corpuscles bounce off a mirror without loss of speed. Force pushed the particles away from the surface.
Refraction - when light passes through a transparent substance from air, the corpuscles are attracted into the substance so travel faster in the substance than in air. The component of the velocity perpendicular to the boundary increases, and parallel to the boundary stays the same.
Describe Huygens’ wave theory of light.
Assumed that light waves travel slower in a transparent substance than air.
Light should diffract around tiny objects and two coherent light sources should interfere with each other.
Why did scientists prefer Newton’s theory?
Newton has a stronger scientific reputation.
The wave theory was considered in terms of longitudinal waves so couldn’t explain the polarisation of light.
It wasn’t possible to measure the speed of light.
What was the significance of Young’s double slit experiment?
Show interference - wave property, which challenged corpuscular theory.
Produced an interference pattern of equally spaced bright and dark fringes. Corpuscular theory couldn’t explain interference patterns, wave theory could.
Describe Maxwell’s theory of electromagnetic waves.
Showed mathematically the speed of electromagnetic waves in free space.
Showed that waves are transverse.
Electric waves and magnetic waves are in phase and perpendicular to each other. Light consists of electromagnetic waves.
Hertz’s discovery of radio waves.
Radio waves produced by the spark gap transmitter spread out from the spark gap and pass through the detector loop, which made the sparks jump across the gap.
Radio waves reflect off a metal plate, and can be polarised.
How did Hertz measure the wavelength and speed of radio waves?
Produced stationary waves using a flat metal sheet to reflect the waves back towards the transmitter.
Measured the wavelength (distance between nodes) and calculated frequency using charge and capacitance. Used known frequency to calculate speed.
What was the significance of Hertz’s experiment?
Radio waves travel at the same speed as light and are electromagnetic waves.
How did Fizeau determine the speed of light?
Passed a beam of light through the gap between two cog teeth to a reflector. The cog was rotated at exactly the right speed so the reflected beam passed through the next gap.
Used frequency of rotation and number of gaps to calculate time taken to reflector and back. Used time and distance to calculate the speed of light.
What is a black body?
A body that absorbs and emits all wavelengths of electromagnetic radiation.
Describe the ultraviolet catastrophe.
Each black body curve has an intensity peak at a particular wavelength, dependent on the temperature.
Wave theory incorrectly predicts that the intensity of radiation should become infinite at smaller wavelengths.
What observation of the photoelectric effect could the wave theory of light not explain?
It couldn’t explain threshold frequency, instant emission and maximum kinetic energy.
It predicted that light of any frequency should cause photoelectric emission and that lower frequency light would just take longer.
Describe Einstein’s photon theory.
Electromagnetic radiation consists of wave packets of energy he referred to as photons.
On order for an electron to escape, it needs to absorb a single photon and use energy equal to the work function.
What was the significance of the photon theory?
Shows wave-particle nature of light.
Particle-like - photoelectric effect
Wave-like - diffraction, interference
