Optics 1

Applied Physics
BS CS/Software Engineering/Information Technology

1st Semester
Optics
Presented By
Dr. Arifa Mirza
Punjab University College of Information Technology
What Is Light?
1) Properties of light
2) Reflection - Mirrors
3) Refraction - Lenses
Properties of Light
Light travels in waves: A wave is a
disturbance that transfers energy from
place to place.
Light travels in straight lines
Laser
Light travels much faster than sound. For example:
1) Thunder and lightning

start at the same time,
but we will see the
lightning first.
2) When a starting pistol

is fired we see the
smoke first and then
hear the bang.
Light travels VERY FAST – about 300,000 kilometers
per second or 186,000 miles per second.
At this speed light

could travel the
equivalent of 8 times
around the world in
one second!
We see things because they reflect light
into our eyes! ALL objects we see either
create light or reflect light!!
Homework
Properties of Light summary
1) Light travels in straight lines and is a form of energy

2) Light travels much faster (a million times faster!) than sound
3) We see things because they reflect light into our eyes
4) Light is a form of energy called Electromagnetic Radiation
5) Visible light is only a small part of the electromagnetic
spectrum; the other parts are invisible to the human eye but
not necessarily the eyes of other animals.
Reflection and Refraction of light
waves
Reflection of light waves
Reflection
For light,
angle of incidence i = angle of reflection r
angles measured with respect to a ‘normal’
Waves and particles are reflected in

exactly the same way.
Reflection and Mirrors
The Law of Reflection
Angle of incidence = Angle of reflection
Regular vs. Diffuse Reflection
Smooth, shiny surfaces
have a regular reflection
Rough, dull surfaces have

a diffuse reflection.
Diffuse reflection is when

light is scattered in
different directions
Refraction
Refraction is the bending of light (it also happens with sound, water and other
waves) as it passes from one transparent substance into another.
Refraction of light waves
•Refraction is when waves speed up or slow down
due to travelling in a different medium
•A medium is something that light waves will travel
through
•Light rays are slowed down by the water
•Causes the ruler to look bent at the surface
• The mediums in this example are water and air
Light hitting
Light hitting at an
straight on is
angle is bent
not bent
The Law of Refraction
Total internal reflection
Light interference
Light interference
• It is the phenomenon in which two waves superpose to form
the resultant wave of the lower, higher or same amplitude. The
most commonly seen interference is the optical interference or light
interference. This is because light waves are randomly generated
every which way by most sources. This means that light waves
coming out of a source do not have a constant amplitude,
frequency or phase.
• The most common example of interference of light is the soap
bubble which reflects wide colours when illuminated by a light
source.
• Example, incandescent bulbs generate a wide range of frequencies
of light, including all colours of the rainbow. Moreover, the light
coming out of the bulb is randomly generated every moment in all
directions. This means that the starting point of the wave generated
may be a maximum, a minimum or any point in between. There is
no way of predicting which phase the wave will start. Such a source
is said to be incoherent.
Two source interference
Double Slit interference
Interference from thin films
Diffraction and the wave theory
Diffraction refers to various phenomena that occur when
a wave encounters an obstacle or opening. It is defined as the bending of
waves around the corners of an obstacle or through an aperture into the
region of geometrical shadow of the obstacle/aperture. The diffracting
object or aperture effectively becomes a secondary source of
the propagating wave.
Single-Slit Diffraction
Diffraction of light is defined as the bending of light
around corners such that it spreads out and illuminates
areas where a shadow is expected.
In the single-slit diffraction experiment, we can observe the bending

phenomenon of light or diffraction that causes light from a coherent source to
interfere with itself and produce a distinctive pattern on the screen called the
diffraction pattern. Diffraction is evident when the sources are small enough
that they are relatively the size of the wavelength of light.
Single Slit Diffraction Formula
We shall assume the slit width a << D. D is the separation between slit and source.
We shall identify the angular position of any point on the screen by θ measured from
the slit centre which divides the slit by a / 2 lengths.
To describe the pattern, we shall first see the condition for dark fringes. Also, let us
divide the slit into zones of equal widths a / 2
Let us consider a pair of rays that emanate from distances a / 2 from each other as
shown below.
What is phase difference?
Phase difference is defined as the difference between any two waves or the
particles having the same frequency and starting from the same point. It is
expressed in degrees or radians.
What is the condition for constructive interference?

The condition for constructive interference is that the path difference should be
equal to an integral multiple of the wavelength.
What is the condition for destructive interference?

The condition for destructive interference is that the path difference should be
equal to odd integral multiple of half wavelength.
Polarization of electromagnetic waves
An electromagnetic wave such as light consists of a coupled oscillating electric
field and magnetic field which are always perpendicular to each other; by convention,
the "polarization" of electromagnetic waves refers to the direction of the electric field.
In linear polarization, the fields oscillate in a single direction. In circular or elliptical
polarization, the fields rotate at a constant rate in a plane as the wave travels.
Polarization is a property applying to transverse waves that specifies the geometrical
orientation of the oscillations. In a transverse wave, the direction of the oscillation is
perpendicular to the direction of motion of the wave.
In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the
displacement of the particles in the oscillation is always in the direction of propagation,
so these waves do not exhibit polarization. Transverse waves that exhibit polarization
include electromagnetic waves such as light and radio waves, gravitational waves, and
transverse sound waves in solids.
Polarizing sheets
A polarizer is an optical filter that lets light waves of a specific polarization pass
through while blocking light waves of other polarizations.

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Applied Physics

BS CS/Software Engineering/Information Technology

1) Thunder and lightning

2) When a starting pistol

At this speed light

1) Light travels in straight lines and is a form of energy

Waves and particles are reflected in

Rough, dull surfaces have

Diffuse reflection is when

In the single-slit diffraction experiment, we can observe the bending

What is the condition for constructive interference?

What is the condition for destructive interference?

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