GPO - Propagation and Velocity of Light - Topic 1

Question 1

What is geometrical optics?

Answer 1

-This help us to understand the basics of light, reflection and refraction and the use of simple optical elements such as mirrors, prisms, lenses

•Also known as ray optics

Question 2

What is Physical Optics?

Answer 2

• This help us to understand the phenomena of light wave, interference, diffraction, and polarization; the use of thin film coatings on mirrors to enhance or suppress reflection
• Also known as wave optics

Question 3

what is the rectilinear propagation of light?

Answer 3

• Rectilinear propagation describes the tendency of electromagnetic waves to travel in a straight line.
• Light does not deviate when travelling through a homogeneous medium

Question 4

What is Huygens’ Principle?

Answer 4

Christian Huygens, believed that light was made up of waves vibrating up and down perpendicular to the direction of the light travels, and therefore formulated a way of visualising wave propagation.

Question 5

What is an optical medium?

Answer 5

Any space through which light travels

Question 6

What are isotropic optical media?

Answer 6

Any optical media which has the same properties in all directions

Question 7

What are homogeneous optical media?

Answer 7

Most optical media have these same properties throughout their mass

Question 8

What are wave fronts?

Answer 8

When light starts out from a point source in an isotropic homogeneous medium, it spreads out uniformly at the same speed in all directions,

-Forming such imaginary spherical surfaces.

Question 9

What is wavelength (λ)?

Answer 9

• Is the distance between successive points of similar phase
• For eg distance between two successive wave crests in the picture or between two successive troughs
• nm

Question 10

What is frequency (ν)?

Answer 10

• Is the number of complete waves produced in one second

* Is expressed in cycle per second called hertz (Hz)

Question 11

What is Amplitutde (A)?

Answer 11

• Is the peak valve of the wave

* Is a measure of height of the wave crest or depth of the wave trough

Question 12

What is Velocity (v) ?

Answer 12

• It’s the rate at which the wave travels

- ms-1

Question 13

What is the velocity of light in a vaccum and for all colours of light?

Answer 13

3 x 10^8 ms-1

Question 14

What is the equation for velocity of light?

Answer 14

velocity of light = frequency x wavelength

v = ν λ

Question 15

A group of light rays is called?

Answer 15

A pencil of rays

Question 16

• The central ray in each pencil is called the

Answer 16

chief ray

Question 17

• A pencil of rays can be…

Answer 17

• divergent (go outwards)
• convergent (go inwards)
• parallel

Question 18

The vergence at a particular point in a pencil of rays is?

Answer 18

is the reciprocal
of the distance from the point to the source or focus
A = 1/a

Question 19

how do we distinguish between diverging and converging rays?

Answer 19

a sign convention is applied (+/-)

Question 20

When is the numerical value of the distance given a positive sign?

Answer 20

If the distance from the point in question to the source or focus is measured in the SAME direction as that in which light rays are directed

Question 21

When is the numerical value of the distance given a negative sign?

Answer 21

If the distance from the point in question to the source or focus is measured in the OPPOSITE direction to that in which light rays are directed

Question 22

What is a dioptre ( 1D) ?

Answer 22

One dioptre (1 D) is defined as the vergence in a pencil of rays at a point one metre to the source or focus

Question 23

What are the symbols given to the vergences?

Answer 23

Diverging = L
Converging= L'

Question 24

What is the distance from A to the object represented by in converging and diverging light rays?

Answer 24

diverging= l
converging= l'

Question 25

When is vergence positive?

Answer 25

At any point in a converging pencil of rays

Question 26

When is vergence negative?

Answer 26

in a diverging pencil