Refraction of Light 3

By : Sariyati,S.T

Refraction is the bending of the path of a light wave as it passes from one material to another material. Refraction occurs at the boundary between the medium and is caused by a change in the speed of the light wave upon crossing the boundary.

The speed of the light in a material/medium depends on its index of refractionThe bigger the index of refraction of a medium, the slower a ray of light will move through the material.

Light Traveling from material with lower refractive index towards higher refractive index, then the light ray will bend towards the normal line.Light Traveling from material with higher refractive index towards lower refractive index, then the light ray will bend away the normal line.

i= 1= angle of incidencer= 2 = angle of refractionni = n1 = index of refraction of the incident mediumnr = n2 = index of refraction of the refractive medium

When light strikes on the border of two medium, its frequency is constant, but its speed and wavelength changesV1 : V2 = n2:n11.f : 2. f = n2:n11 : 2. = n2:n11. n1 = 2 . n2

When the observer is in the air

When the observer is in the water

h=real depthh = apparent depthnw = water refractive indexna = air refractive index =1

1. Light velocity in the air is 3x108m/s. What is the light velocity in the water if its refractive index is 4/32. A ray of light passes through medium A to B with incident angle of 45 and refracted with the angle of 60 .Determine the relative refractive index ofA. medium A to BB. medium B toA3. A ray of light has frequency of 7.5 x 1014 Hz and speed of 3x108m/s in the air.Calculate: a. the wavelength of the light in the air

B. light velocity in the waterC. wavelength in the waterD. its frequency in the water (nwater = 4/3)4.Look at the following picture!

If nglass= 1.5 and nwater=4/3,nair=1 calculate the angle of refraction when light emerged from glass to water () if sin=3/85. The deep of a pond is 2.0 mIf it is fulfilled with water (nwater = 4/3), what is the apparent depth of the pond by an observer above the water surface?6. A fish look at a child located 1m (nwater = 4/3), above a lake surface. What is the apparent height of the child seen by the fish?WaterGlass

Is the incidence angle that make the refracted angle equals to 90 n1 sin ic = n2 sin 90n1 sin ic = n2 sin ic = n2: n1

Total internal reflection (TIR) is the phenomenon of the reflection of all the incident light off the boundary.

TIR only takes place when :a light ray strikes from more dense medium towards less dense medium.the angle of incidence is greater than the critical angle.

Diamond sparklingPeriscopeOptical fiber, used in :medical technology/endoscopycommunication

Is the separation of visible light into its different colors (ROYGBIV)Caused by the different frequency of the light in the prismExample : rainbow, when white light passes through a prismhigher frequency (lower wavelength) violet light to travel slower through crown glass than the lower frequency (higher wavelength) red light

Three Convenient ray in convex lensAny incident ray parallel to the principal axis will refract through the lens and travel through the focal point on the opposite side of the lens.Any incident ray through the focal point will refract through the lens and travel parallel to the principal axis.An incident ray which passes through the center of the lens will in affect continue in the same direction that it had when it entered the lens.

NoObject LocationPictureImage Character1

2

3

4

5The object is located in front of F

The object is located at F

The object is located between 2F and F

The object is located at 2F

The object is located beyond 2F

Virtual, upright,bigger

No image

Real,inverted, bigger

Real, inverted, same size

Real, inverted, smaller

Three Convenient ray in concave Lens

Any incident ray traveling parallel to the principal axis of a diverging lens will refract through the lens and travel in line with the focal point (i.e., in a direction such that its extension will pass through the focal point).Any incident ray traveling towards the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.An incident ray which passes through the center of the lens will in affect continue in the same direction that it had when it entered the lens.

located on the object' side of the lensa virtual imagean upright imagereduced in size (i.e., smaller than the object)

1/f = (n-1)(1/r1+1/r2)

f = the focal length of the lensn= refractive index of lens materialr1= radius of the first lensr2= radius of the second lensr1 and r2 positive for convex surfacer1 and r2 negative for concave surfacer1 and r2 for plane surface

Check your understanding1. Determine the image distance and image height for a 5-cm tall object placed 20.0 cm from a double convex lens having a focal length of 15.0 cm2. A lens (its refractive index =1.5) has convex surface its radius of 20 cm, and concave surface with radius of 40 cm. Calculate its focal length and determine whether it is convex or concave lens3. The focal length of a lens(refractive index =1.5) when it is in the air is 12 cm. What is its focal length when it is put in the water (refractive index=4/3)

Lens PowerP = 1/f (m) or P =100/f (cm)

P =power of lens (diopter)f = focal length of the lens (m)