wu1c3 by Adel Khamis

8/14/2019 wu1c3 by Adel Khamis

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Unit one-1-Chapter Three

Light as wave motion

Light:

Light is a branch of

waves.

It consists of .. field and

field perpendicular to each other and

. to the direction of

propagation, therefore it

considers as (longitudinal

transverse) waves, and it

(required / not required)

medium to propagate.

Propagation of light:

Light propagates in

..

Reflection of light:

Definition. :

The laws of reflection:

..

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Refraction of light:

D

efiniti

on:

If the angle of incident is zero, the ray fall (normal /

perpendicular) to the surface, it

..

G.R:.

When the ray incident with angle equal zero it

suffers no refraction.

..

..

The optical piece used in the experiment is semi

circular prism, and the light beam fall on the plane

surface.

..

..

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The laws of refraction:

First Law states:

Second law states:

Refractive index (n:)

Definition :

.

G.R:

The value of refractive index is greater than one.

.

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v

cn =

V

C

sin

sin(n)indexrefractive ==


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...........

..........21=n

..........

..........=

............

...........=

..........

..........21=n


Relative refractive index (1n2:)

Definition.. :

F

actors affected on relative refractive index

.. ,..

Factor affected on absolute refractive index

..

Relation between relative and absolute index:

* The first medium(1) has velocity of

light = V1

* The secondmedium (2) hasvelocity of light =

V2

* The first medium(air) has velocity

of light = C

* The second

medium (1) hasvelocity of light =V1

* The first medium(air) has velocity

of light = C

* The second

medium (2) hasvelocity of light =V2

C = x.. C = . x.

n V = n V

.......

.......

.......

.......

.......

.......21 ===n

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==sin

sin

2v

1vn

21

..........

..........

2

1 =V

V


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The angle of incidence in a medium is 60 and the

angle of refraction in the other medium is 30, the

relative refractive index from the first to the second

medium is .. and that from the

second to the first is..

Refractive index of air =

.

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Snells law:

*

)1(.........

........21 =n

(related to absolute refractive index).

*

)2(...........

.........21 =n

(related to velocity)

From (1) and (2)

*

)3(.............

............

1

2 =n

n

*

)4(sin

sin

2

1

V

Vbut =

From (3) and (4)

Prove that:

12

21n

1n =

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.......sin........sin21nn =


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N.B:

The medium, which has less velocity, considered

optically (denser/ less dense) than the medium,which has great velocity.

What is meant by:

The absolute refractive index of glass = 1.5

..

Give reason for:

Light passing into a denser medium is bent toward

the normal.

..

Light passing into less denser medium is bent away

from the normal.

..

You can see your image at window glass nightly,

while you cant see it at day time.

..

Examples:

Given that the velocity of light in air = 3x108 m/s

and that in water equal 2x108 m/s, if a light ray fall

with angle of 30 with water surface, find the angle

between refracted ray and reflected ray.

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[8445]

A light ray falls on the surface of glass of absolute

refractive index 1.5 with angle of incidence that is

equal to 30. Find the angle of refraction.

[19.47]

Given that the absolute refractive index for water is

4/3 and that for glass is 3/2 find:

a) The relative refractive index from water to glass.

b) The relative refractive index from glass to water.

[9/8,8/9]

An incident ray by an angle 48.5 on one face of a

glass rectangular block (n = 1.5) the angle of

refraction is and the angle of

emerge is

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Give reason:

When white light refract, it

separated into seven colors.

Interference of light (young experiment:)

Explain an experiment to illustrate the interference of

light by using of double slit:

.

..

..

.

Where:

y.. =

d =

R =

=

N.B:.

1meter (m) = Angstrom (.)

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d

Ry =


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Give reason for:

Monochromatic light is used in Youngs experiment.

The fringes become clear when the distance

between two slits become small.

.

Red light is preferred to violet in young experiment.

.

In youngs experiment when a red light of

frequency 1x1015 Hz is used the distance between

the fringes was 2 mm. Calculate the distance when

violet light of frequency 0.6x1015 Hz is used.

.

.

.

[3.3x10-3m]

What is the benefit of double slit in young

experiment.

Diffraction of light:

Definition :

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The aperture or the slit must be (equal or

less than / larger than) the wavelength of the

light.

If the aperture has circular shape

the diffraction appear at the screen

as airys disk, where it consists of

. at the middle followed

by rings.

If the aperture has rectangular

shape the diffraction appear as

Give reason:

Sound waves diffract at edges of the doors and windows but light

not.

.

Question:

What do you know about Airys disk

.

.Light as wave motion:

Light considers as wave motion because:

.

.

.

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.

.

Critical angle and total reflection:

When a ray of light passes

from a denser optical medium

to a less dense medium, it

refracts . the

normal.

By increasing of the incident angle, the refracted

angle will (increase/ decrease) to reach ..

By increasing of the incident angle, the emerge ray

will return at the same medium forming

...

Critical angle:

Definition. :

If the incident angle is smaller than the critical

angle the ray will .; while it will

if the angle of incident is greater than the

critical angle.

Find the relation between the critical angleand the absolute reflective index:

Prove that:

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csin

1n

=


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If the critical angle for a medium to air is 45 then

the absolute refractive index is..

[1.4]

N.B:

anm=

csin

1n

=

mna=

c21 sinn =

Totally reflection:

Definition

G.R:.

The totally reflection is preferred than the normalreflection.

Factors required for total reflection:

If the critical angle of water is 45 and for glass =

40. Find the relative refracted index between glass

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and water. And find the critical angle of light from

glass to water.

[0.90903,6522]

Calculate the critical angle between glass and

water given that their refractive indexes are 1.6

and 1.33 respectively.

[5613]

N.b:.

From less dens medium to dens medium:

If = 0 then

(G.R)

.

If > 0 then

From dens medium to less dens medium:

If = 0 then

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Ifc > > 0 then

If = c then ...,=

If > c then

Application of totally reflection:

Fiber optics (Optical fibers:)

It is a fine hollow fiber of a

transparent material has (small/

high) critical angle.

When the incident ray enters, it falls at the surface

with an angle greater than the critical angle,

therefore the ray will..

Then the ray will emerge from the other end of the

fiber.

It is widely used as . in medicine and

.. in communications.

Mirage:

Definition. :

..

..

The layer of air with contact to the

earth surface (high / low) in temperature and

became (dens / less dens)

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The upper layer will be (denser / less dens) than

the lower layer.

The ray falls from the object will refract many timethrough the layer of hot air (increasing/ decreasing)

of its angle.

When the angle of incident becomes (greater/

smaller) than the critical angle the ray will

. forming.

Totally reflected prism:

It is used to change the path of light rays either by 90 or 180.

Draw a diagram to change the path of light ray by

180. Which used in..

Draw a diagram for binoculars.

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Draw a diagram to change the path of light ray by

90. Which used in..

Give reason:

The reflected prism is preferred to metallic mirrors.

..

..

Reflected prism is painted with cryolite (reflected

layer.)

..

..

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1A212123


Deviat

ion

with a

triang

ular

prism:

From the

previous

diagram:

A + 3=

..

1 + 2

+ 3 =

.

A =

.. + .(1)

= + .(2)

1 - =(3)

2 - =(4)

From (2) and (3) & (4)

- + . - =

) + .( - . + =

From equation (1)

.. - . + . =

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.

[1.225,15]

Angle of deviation ()

Definition.. :

Factors affected on the angle of deviation:

.

.

.

Tracing the path of the ray through the prism:

The deviation angle decrease by increasing of the

incident angle to a certain value then it increases

by increasing of the incident angle.

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1


The ray will

..

1 =

2 =

.

1. =

1.. =

. =

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2. =

The immerge ray

Reflected ray

Notes:

From the graph of minimum deviation, when the

angle of incident increases then the angle of

deviation .. until it reaches then

by increasing the angle of incident, the angle of

deviation will.

If the angle of incident is less than the value in

which the graph starts therefore the prism acts as

..

The minimum angle of incident is corresponding to

angle of incident at the second face equal and the emigrant ray will be .. to the

second surface of the prism, and the emerge angle

=

In the case of minimum deviation:

The refracted ray will be .. to the base of prism.

1 = 2 =

A.. =

..........

........ =

And

1 = 2 =

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.. - .. =

..........

.................. +=

*

sin

sin=n

+

=

.....

.....sin

.....

..........sin

n

Examples:

In an experiment it was found that the angle of

minimum deviation is 48.2, given that the angle of

the prism is 58.8. find the refractive index of the

material of the prism.

[1.64]

A triangular prism of refractive angle 60 adjusted

to the minimum deviation position; when the angleof min. dev. is 37.2 find its refractive index.

[1.5]

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Experiment to determine the ray path through a

glass prism and its refractive index:

The dispersion of light by a triangular prism:

The angle of deviation depends on

.., which depends on ... Therefore,

each color of light going to deviate by a certain angle,

deference than the other color.

Give reason for:

When beam of white light falls on a triangular

prism adjusted in min. deviation, the emergent ray

deviated into different colored rays (spectrum.)

..

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The violet ray has the biggest deviation (max. ).

but the red ray has the least deviation (min. .)

..

Question:

The relation between the angle of deviation and

the wavelength of light is (directly / inversely)

proportional.

The relation between angle of refraction at the first

face and angle of incident at the second face is

(directly / inversely) proportional.

Draw a graphical relation between angle of

refraction at the first face 1 and angle of incident

at the second face 2

The mathematical relation is

..

The intersected point with Y axis indicates

The intersected point with X axis indicates

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A


Trace the light ray in the opposite figure where n =1.5

The thin prism:

It is a triangular prism, with an angle not more than10. It is always in a position of minimum deviation.

In case of the small angles the angle in radian unit

is equal to its sin.

2

.......2

................ +

=n

...........

................. +=n

n.. + =

.. - . =

= A) - ..(The relation between and A can be drawn as:

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n


Mathematical relation :

Slope

The point of intersection with Y-axes=

The point of intersection with X axes =

The relation between and n can be drawn as:

Mathematical relation :

Slope

Factors affects :...

N.B:.

Rule Case of application

......................

All cases Min

deviation

Thin

prism

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..

X Min

deviation

Thin

prism

X X Thin

prism

In case of thin prism for the red color:

r =In case of thin prism for the blue color:

b=..

(b - r) known as the angular size; it is also known

as or . or .

.. or..

Define angular size :

..

Give reasons:

Thin prism is always in minimum deviation.

.

Prove that the angular size equals A (nb - nr)

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Factors affect angular size:

.

.

A thin prism has an angle of 5 its refractive index

1.6 produces angle of deviation that is equal to

..

[3]

A ray of light falls on a thin prism with an angle of

deviation 4 and its refractive angle 8 its refractive

index is

[1.5]

Depressive power (:)Definition. :

Rule.. :

Prove that:

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1

=

=

n

nrnbrb


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Factor affects Depressive Power (:)

.

N.B:.

= y = .. (Relation between for the blue

color and for the red color)

n = ny = .. (Relation between n for the blue

color and n for the red color)

(total = )

b - r (total.. = )

(total = )

b - r (total.. = )

wu1c3 by Adel Khamis

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