Unit 4: Wave Nature of Light

Question 1

Particle Theory

Answer 1

this was the more popular theory because Newton was the main advocate, this theory believed that light consisted of a steam of fast moving particles

Question 2

Classical Wave Theory

Answer 2

Hooke discovered the wave theory in 1655 & Huygen expanded the theory in 1678, this theory believed that light travelled as a wave, explained by Huygens principle; every point on the wave front can be considered as a point source of tiny secondary wavelets that spread out in front of the wave at the same speed as the wave itself

Question 3

Rectilinear Propagation

Answer 3

Particle Theory- light appears to travel in a straight line since it consists of particles with high speeds
Wave Theory - the wave propagates away from the source & each point acts at a point source for a new spherical wavelet

Question 4

Diffraction

Answer 4

Particle Theory - light can’t travel around comets like waves this is a collision between light particles at the edges of the slit
Wave Theory - when each point passes through an opening it acts as a point source for new spherical wavelets

Question 5

Reflection

Answer 5

Particle Theory - light particles experience perfectly elastic collisions that follows the laws of motion
Wave Theory - a wave bounces off a material & travels back in the direction from which it originated

Question 6

Refraction

Answer 6

Particle Theory - if particles speed increases it will bend toward the normal and accelerate at the boundary when passing mediums
Wave Theory - the speed of wave fronts travelling into two medias causing the waves to bend toward or away from the normal

Question 7

Dispersion

Answer 7

Particle Theory - different colours of light have different angles of refraction & masses
Wave Theory - the white light is made of colours of the spectrum with different wavelengths for each one

Question 8

Partial Reflection/Partial Refraction

Answer 8

Particle Theory - newtons “theory of fits” is when light sometimes arrives at a surface in a ‘fit’ of reflecton or refraction
Wave Theory - when waves move from a slow medium to a fast medium, or visa versa it experiences reflection & transmissions

Question 9

Factors that affect an interference pattern

Answer 9

1. as frequency of the sources increases, nodal lines move closer together
2. when the source separation increases, the number of nodal lines increases
3. if two sources are out of phase by 180, the constructive & destructive interference location changes
4. if left source is delayed, the lines shift to the left

Question 10

Younge’s double slit experiment

Answer 10

he used a single source in front of two pinholes that were very close together that was shown on a screen of interference light and dark fringes

Question 11

Younge’s double slit experiemnt significance

Answer 11

confirm that the wave theory was true

Question 12

Classical wave theory problems

Answer 12

what was the source vibration?
how could light travel through a vacuum such as space?

Question 13

Maxwell’s Equation’s

Answer 13

1. electric charges in space produce an electric field & currents produce a magnetic field
2. magnetic field lines form continous closed loops that have neither a beginning nor end
3. a changing electric field produces a magnetic field
4. a changing magnetic field produces an electric field

Question 14

Properties of EM waves

Answer 14

1. EM waves are made up of alternating oscillating electric & magnetic fields
2. electric & magnetic fields are perpendicular to each other & oscillate in phase
3. the direction of propagation of the wave is perpendicular to both electric & magnetic
4. EM waves travel at the speed of light, c, in a vacuum

Question 15

State EM theory of light

Answer 15

oscillating charge creates an electric charge which creates an oscillating magnetic field

Question 16

How did Maxwell’s equations solve classical wave theory

Answer 16

the changing of electric & magnetic fields create a self-propagating wave that can travel through empty space

Question 17

Why do we see swirling colour when oil floats on water

Answer 17

different parts of the oil on water is constructive (bright-red) and destructive (dark-blue) interfernece creating the swirling oil

Question 18

Difference between diffraction patterns and double slit interference patterns

Answer 18

• d (slit seperation) becomes w (width)
• x (distance from central max) become y
• the 1/2 was used with the minima formulas for the double slits & is now used with the maxima formulas

Question 19

EM spectrum

Answer 19

Radiowave, microwaves, infered radiation, visable light, UV light, x-ray, gamma rays

Question 20

Polarization

Answer 20

process of removing one of the components

Question 21

How does polarizing filters work

Answer 21

when two polariod filters are aligned perpendicular to each other no light passes through, when they are aligned parallel light will pass through

Question 22

Scattering of light

Answer 22

change in direction of light waves as a result of collisions

Question 23

What is a diffraction grating & how does its effect interference?

Answer 23

• a device with a large number of equally spaced parallel slits that produces interference patterns
• interference patterns from lasers can create lines on a photographc films