Reflection and Refraction

Question 1

what things could happen to a wave if it was incident on an interface between two different media

Answer 1

• it could be absorbed, transmitted or reflected

- and by it i mean its energy

Question 2

what does the law of reflection state

Answer 2

• the angle between the incident ray and the normal drawn at the point of reflection
• is equal to the angle between the reflected ray and the normal
• in the plane of reflection

Question 3

what would the effect of increasing the angle of the incident ray be

Answer 3

a greater proportion of the light would be reflected

Question 4

what is refraction

Answer 4

• when a ray of light at an angle to the normal changes direction when it passes from one medium to another
• due to a change in the speed of the wave

Question 5

what is a wavefront

Answer 5

• a line or surface on a wave

- along which all the points are in phase

Question 6

what would the distance between the wavefronts be

Answer 6

a wavelength

Question 7

what does a decrease in the velocity of a wave when entering a denser medium do to its wavelength

Answer 7

• it decreases it
• as with wavelength = velocity / frequency where frequency is constant
• a decreased v leads to a decreased lambda

Question 8

how does a reduction in the wavelength impact the waves wavefront

Answer 8

• it causes the wavefront to change direction
• as the wavefronts are perpendicular to the motion of the wave
• the path of the wave would be deviated towards the normal when the speed is decreased

Question 9

how do waves therefore act when they are going from a less dense to denser material and vice versa

Answer 9

• when a wave travels from a less dense to denser medium, it refracts towards the normal
• when it goes from a denser to less dense material, it refracts away from the normal

Question 10

how can that relationship be related to the speed of the wave

Answer 10

• when the speed of a wave increases it refracts away from the normal
• when the speed of the wave decreases it refracts towards the normal

Question 11

what would the ratio of the speed that light travels through air and glass be called

Answer 11

the refractive index

Question 12

how would you calculate the refractive index from medium 1 to medium 2

Answer 12

• speed in medium 1 / speed in medium 2

- 1n2 = v1 / v2

Question 13

what is the ratio of the speeds also equal to due to the analysis of wavefront progressions

Answer 13

the ratio of the incident angle and the refracted angle

Question 14

what equation can then be written from that deduction

Answer 14

1n2 = sin theta1 / sin theta2

Question 15

what does Snell’s law state

Answer 15

• that the refractive index for a wave travelling from one medium to another is given be the expression
• 1n2 = sin theta1 / sin theta2 = v1 / v2

Question 16

when only working with light, what could snells expression be written as and why

Answer 16

• n = sin i / sin r = c / v
• i represents the angle of incidence
• r represents that angle of refraction
• c is the speed of light in air / vacuum
• v is the speed of light in the (2nd) medium

Question 17

for light travelling from a medium of refractive index n1 to one of refractive index n2 at angles theta1 and theta2, the equations for both are n1 = c / v1 and n2 = c / v2. how would you rearrange this equation to show that the products of the refractive index and its corresponding angles equal each other

Answer 17

• n1 = c / v1 and n2 = c / v2
• c = n1 v1 and c = n2 v2
• n1 v1 = n2 v2
• v1 = n2 v2 / n1
• v1 / v2 = n2 / n1
• as 1n2 = v1 / v2 from the normal equation, 1n2 = sin theta1 / sin theta2
• n2 / n1 = sin theta1 / sin theta2
• n2 x sin theta2 = n1 x sin theta1

Question 18

when does total internal reflection occur

Answer 18

when the angle of incidence is grater than the critical angle

Question 19

for a ray of light passing through glass from air, what would happen if the angle of incidence is less than the critical angle

Answer 19

• some light would be reflected

- while some would be refracted

Question 20

what would happen if the angle of incidence was equal to the critical angle

Answer 20

• the light would be refracted to 90 degrees, perpendicular to the normal
• total internal reflection would just occur

Question 21

what happens when the angle of incidence is greater than the critical angle

Answer 21

total internal reflection fully occurs

Question 22

what is the critical angle

Answer 22

• the angle of incidence above which total internal reflection occurs
• aka the angle where the refracted ray is perpendicular to the normal

Question 23

for light travelling from a medium of refractive index n1 to one of lower refractive index n2, wht expression would be used to calculate the critical angle

Answer 23

• sin C = n2 / n1

- where C = critical angle