physics refraction final

$: Physics Refraction Final$
Refraction of Light

Duran CastelinoRoll No: 6

LightLight is a form of energy.

We see an object when the light energy leaving it enters our eye.

Objects which give out their own light are called luminous.

Objects that do not give out light but scatter the light that falls on them are called non-luminous.

Light travels in straight lines in the form of a transverse wave

RefractionRefraction is the bending of light when it enters from one transparent medium into another transparent medium of different density.

Caused by different speeds of light in different media.

When a ray of light passes from a rare medium to a dense medium, it bends towards the normal, as its velocity decreases.

When a ray of light passes from a dense medium to a rare medium, it bends away from the normal, as its velocity increases.

Refraction in Everyday LifeWe see refraction in everyday life:

Water mirage on the road.

Distortion of images viewed through a glass prism.

Distortion of objects viewed in water.

Laws of Refraction

Incident ray

Refracted ray

Emergent ray

Angle of incidence

Angle of refraction

normal

Angle of emergence

The incident ray, the normal and the refracted ray lie in the same plane.Snell’s Law: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant quantity which is called the refractive index of the second medium w.r.t the first.

riμ

sinsin=

Refraction through Rectangular Glass Slab


When light passes through a rectangular glass block it proceeds from:

air (a rarer medium) to

glass (a denser medium) to

air (a rarer medium)

Speed of light in air:3*108 ms-1

Speed of light in glass:2*108 ms-1

Refractive Index of glass w.r.t air

aμ g = 3*108/2*10 = 1.5


Path of Light Ray

In the figure:

AB Incident Ray

BC Refracted Ray

CD Emergent Ray

i angle of incidence

r angle of refraction

e angle of emergence

l lateral displacement

iA

B

r

eC

D

l

M

N

P

When ray AB enters the glass slab at point B, it bends towards the normal BN and proceeds to point C as i > e.

At point C, it bends away from the normal CP along path CD.


CD is parallel to AB as i = e

Incidence, Refraction & Emergence

iA

B

r

eC

D

l

M

N

P


iA

B

r

eC

D

l

M

N

P

The perpendicular distance between the directions of incident and emergent rays is lateral displacement l.

Factors affecting lateral displacement:

The angle of incidence

Thickness of the rectangular slab

Material of the slab

Lateral Displacement


If the incident ray enters the slab at an angle to the normal, then the direction of the ray changes on entry and exit.

If the light ray enters the glass slab parallel to the normal (angle of incidence i = 0), then it travels without deviation through the slab.

Condition for Zero Deviation

Refraction through a Prism

Refraction through a PrismA prism is a

transparent refracting medium

bounded by two plane surfaces

inclined at some angle

Thus it has 2 triangular faces and three rectangular faces.

When conducting experiments, the prism is made to rest on its triangular face.

Refraction through a PrismPath of Light Ray

Incident ray TP forms angle of incidence i

It bends towards the normal PN making an angle of refraction r

The refracted ray PO strikes AC at an angle of incidence r1


Emergent ray OQ bends away from normal forming an angle of emergence r1.

r + r1 = A and i + i1 = A + δ

Incidence, Refraction & Emergence

Angle of deviation is the angle between the directions of the emergent ray and the incident ray.

δ = i + i1 - A

Angle of deviation depends on:


The angle of incidence (i)

The angle of the prism (A)

The material of the prism

The colour or wavelength of light used

Angle of Deviation

As the value of the angle of incidence increases the value of the angle of deviation decreases to a minimum value before increasing again.

This minimum value is the angle of minimum deviation.

At the position of minimum deviation, the angle of incidence is equal to the angle of deviation

i = i1 and r + r1

Refraction through a PrismMinimum Deviation

Critical angle of a medium is the angle of incidence in the medium for which the angle of refraction in air is 90o

Critical angle for glass is 42o

If the angle of incidence become more than the critical angle, more refraction cannot take place and the ray is totally internally reflected i.e. the surface behaves like a mirror.

Refraction through a PrismCritical Angle

A total refracting prism has an angle of 90o between its two refracting surfaces and its other two angles of 45o each.

The light incident normally on any of its surfaces, suffers total internal reflection inside the prism.

Refraction through a PrismTotal Internal Reflection

Total Reflecting prisms are used to:

Deviate a ray of light through 90O or through 180O

Erect an inverted image without producing deviation in its path

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