Optics Problems - Applied Physics - Lecture Slides, Slides of Applied Chemistry

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LECTURE ON NUMERICAL

PROBLEMS IN OPTICS

Light :-

i) Light is a form of energy which helps us to see objects. ii) When light falls on objects, it reflects the light and when the reflected light reaches our eyes then we see the objects. iii) Light travels in straight line. iv) The common phenomena of light are formation of shadows, formation of images by mirrors and lenses, bending of light by a medium, twinkling of stars, formation of rainbow etc.

• The overall study of how light behaves is called optics.
• The branch of optics that focuses on the creation of images is called geometric optics, because it is based on relationships between angles and lines that describe light rays.

Some Definitions

• Absorption
  • When light passes through an object the intensity is reduced depending upon the color absorbed. Thus the selective absorption of white light produces colored light.
• Refraction
  • Direction change of a ray of light passing from one transparent medium to another with different optical density. A ray from less to more dense medium is bent perpendicular to the surface, with greater deviation for shorter wavelengths
• Diffraction
  • Light rays bend around edges - new wavefronts are generated at sharp edges - the smaller the aperture the lower the definition
• Dispersion
  • Separation of light into its constituent wavelengths when entering a transparent medium - the change of refractive index with wavelength, such as the spectrum produced by a prism or a rainbow

• A lens is an optical device that is used to bend light in a specific way.
• A converging lens bends light so that the light rays come together to a point.
• A diverging lens bends light so it spreads light apart instead of coming together.

• Mirrors reflect light and allow us to see ourselves.
• A prism is another optical device that can cause light to change directions.
• A prism is a solid piece of glass with flat polished surfaces.

Reflection

• Images appear in mirrors because of how light is reflected by mirrors.
• The incident ray follows the light falling onto the mirror.
• The reflected ray follows the light bouncing off the mirror.

Reflection

• In specular reflection each incident ray bounces off in a single direction.
• A surface that is not shiny creates diffuse reflection.
• In diffuse reflection, a single ray of light scatters into many directions.

Law of reflection

• A light ray is incident on a plane mirror with a 30 degree angle of incidence.
• Sketch the incident and reflected rays and determine the angle of reflection.

30 o^30 o

Mirror

A dentist uses a mirror to

look at the back of a second

molar ( A ). Next, she wishes

to look at the back of a

lateral incisor ( B ), which is

90° away. By what angle

should she rotate her mirror?

A. 90°

B. 45°

C. 180°

A

B

Specular vs. Diffuse Reflection

Diffuse Reflection

• The surface is rough at distance scales

near or above the wavelength of light

• Almost all surfaces reflect in this way!

Two plane mirrors form a right angle. How many images of the ball can you see in the mirrors?

A. 1

B. 2

C. 3

D. 4

Refraction

When a ray of light crosses from one material to another, the amount it bends depends on the difference in index of refraction between the two materials.

Refraction

Water

Refraction is the Air bending of light as it passes from one medium into another.

refraction

N

θw

θA

Note: the angle of incidence θA in air and the angle of refraction θA in water are each measured with the normal N.

The incident and refracted rays lie in the same plane and are reversible.