M7 Topic 2: Wave Model

Question 1

what is diffraction

Answer 1

the spreading out of a wave as it passes through an opening or moves past an obstacle

Question 2

how is the maximum diffraction achieved

Answer 2

when the aperture is the same width as the wavelength of the incident waves

Question 3

what where the two classical models of light

Answer 3

• Newton’s particle model

- Huygen’s wave model

Question 4

what did Newton’s particle model state (3)

Answer 4

• light consists of solid particles called corpuscles with intrinsic properties that include size and shape
• Matter and light can interact, by bending the path of light particles and light particles cause vibrations in matter
• light moves faster in water

Question 5

what did Huygens wave model state (4)

Answer 5

• light consisted of waves that move rapidly through aether
• Light waves propagate through the aether as a medium
• light propagates in way where every new wavefront acts as a new source for spherical waves
• light moves slower in water

Question 6

why was Newton’s theory discredited and Huygens model seen as the most correct model (2)

Answer 6

• newtown had no practical proof that he’s model would work

- discredited due to experiments showing light had wave qualities

Question 7

what experiments discredited newtons particle model (3)

Answer 7

• Young’s double slit experiment to demonstrate interference
• the Poisson/Arago spot due to diffraction
• Foucault’s water experiment showed that light moves slower in water

Question 8

what would you see in a single slit experiment (2)

Answer 8

• a central maximum that is twice as wide as subsequent maxima
• subsequent maxima are significantly smaller than the central maximum

Question 9

what would you see in a double slit experiment (3)

Answer 9

• widely spaced fringes further from the centra maximum due to deconstructive interference between the two slits
• closely spaced fringes near the central maximum
• coloured bands and black bands (interference pattern)

Question 10

what equation is used to determine whether light is constructive or destructive interference at a point

Answer 10

dsinθ= mƛ

Question 11

what does each symbol in the interference equation and give units (4)

Answer 11

d= the slit separation (metres (m))
θ= the angle between the point on the screen and the
perpendicular bisector, between the slits ( ° )
m= number of peaks away from the central maximum
ƛ= the wavelength of the lightwaves(metres (m))

Question 12

what is the equation for fringe seperation

Answer 12

Δx = ƛL/d

Question 13

what does each symbol in the fringe seperation equation and give units (4)

Answer 13

Δx = the fringe separation (metres (m)
ƛ = the wavelength of the light waves (metres (m))
L =the distance of the slits from the screen
d = the slit separation (metres (m))

Question 14

what is a diffraction grating

Answer 14

a screen with multiple slits in it allowing many individual slits of light

Question 15

what is unpolarised light

Answer 15

light that has electric field oscillations in all orientations

Question 16

what is polarised light

Answer 16

light that has electric field oscillations in one orientation only

Question 17

what polarises light

Answer 17

poloroid filters

Question 18

what types of polaroid filters are there (2)

Answer 18

-polarisier, the first polarising lens, unpolarised light passes through
Analyser: the lens polarised light passess through

Question 19

how much of the electric field orientations are removed when unpolarised light pases through the polariser

Answer 19

50%

Question 20

how do polaroid filters work

Answer 20

the long molecules that make up the filter all align in one direction, allowing for only one component of the electric field through

Question 21

what law is used to calculate the percentage of light left once the light passess through the analyser filter

Answer 21

Malus’ law

Question 22

what is Malus’ law

Answer 22

I=Iₘₐₓ cos²θ

Question 23

what does each symbol in Malus’ law represent (3)

Answer 23

I= the intensity of the light through the analyser (candela (cd))
Iₘₐₓ= the intensity of the light through the polariser (candela (cd))
θ= the angle of the analyser compared to the polariser ( ° )

Question 24

how is light polarised via reflection

Answer 24

light must reflect at Brewster’s angle so that there is a 90° angle between the reflected and refracted waves, the reflected light will be linearly polarized