waves and light

Question 1

what is a wave?

Answer 1

A wave is the transfer of energy from a vibrating source

Question 2

Amplitude

Answer 2

the maximum displacement from rest position or equilibrium position. (a)

Question 3

Equilibrium positon

Answer 3

The level of still water before a wave passes through

Question 4

Wavelength

Answer 4

the distance between two points in phase

Question 5

Frequency

Answer 5

the number of waves moving past a point in 1s

Question 6

Period and Speed of propagation of a wave

Answer 6

Period : the time taken to generate a full wave. Is also the time taken for any given point on a wave to move the distance of one wavelength. (T) (T=1/f)
Speed : the distance moved by a wave in one second. (v) (v=(WL)/T) (v=WL x f)

Question 7

Transversal waves

Answer 7

A wave which travels in a direction perpendicular to the direction of vibration

Question 8

Longitudinal waves

Answer 8

A wave which travels in a direction parallel to the direction of vibration

Question 9

The “normal”

Answer 9

the straight line that is perpendicular to the reflecting surface

Question 10

Angle of incidence and angle of reflection

Answer 10

Angle of incidence : (i) is the angle between the incident ray and the normal
Angle of reflection : (r) is the angle between the reflected ray and the normal

Question 11

What do all waves follow?

Answer 11

The Laws of reflection :

1. The incidence ray, reflective ray and normal at the point of incidence all lie on the same plane.
2. The angle of incidence is equal to the angle of reflection (i = r)

Question 12

Refraction

Answer 12

The change in the direction of a wave when it crosses a boundary.

Question 13

How does the refracted ray bend when the ray goes from a less dense to a more dense medium (vice-versa)

Answer 13

Less dense to more dense : The ray bends closer to the normal (i > r)
More dense to less dense : The ray bends further from the normal (i < r)

Question 14

What is the refractive index a measure of?

Answer 14

the ratio of the speed of light in a vacuum to the speed of light in that medium.
Refractive index =
(speed of light in vacuum) / (speed of light in a medium)
n = c / v

Question 15

What is real and apparent depth?

Answer 15

Refractive index of medium with respect to air =
(real depth) / (apparent depth)

Apparent depth : is the higher depth at which something appears due to the water-air boundary refracting light at the bottom of the pool
Real depth : is the actual depth at which something is

Question 16

Critical angle

Answer 16

The angle of refraction is 90 degrees

Question 17

What conditions are necessary for total internal reflection to occur?

Answer 17

The ray will totally reflect, this will occur (1) when the light ray travels from an optically denser medium towards an optically less dense medium, and (2) the angle of incidence must be greater than the critical angle.
(sin c) = 1 / n

Question 18

What image is created by a reflection of a plane surface vs. a rough surface? (regular vs diffuse reflection)

Answer 18

Plane surface : The light will all be parallel, very harsh on the eye
Rough surface : The light will be scattered in different directions

Question 19

What are the laws of refraction?

Answer 19

1. The incident ray, refracted ray and normal at the point of incidence all lie on the same plane
2. For two given media, the ration sin(i) / sin(r) is a constant where i is the angle of incidence and r is the angle of refraction (Snell’s Law)

Question 20

when is i = 0 degrees

Answer 20

i is equal to 0 degrees when the ray of incidence lies at 90 degrees