Optics and Diffraction

Question 1

What is the electromagnetic spectrum?

Answer 1

A continuous sequence of all possible wavelengths of EM radiation that may be emitted as photons

Question 2

How do all wavelengths of electromagnetic radiation travel?

Answer 2

At the speed of light and transfer energy as transverse waves

Question 3

What is the relationship between wavelength and frequency in electromagnetic radiation?

Answer 3

They are inversely proportional

Question 4

What is frequency directly proportional to in relation to photons?

Answer 4

Photon energy

Question 5

What defines coherent waves?

Answer 5

Two or more waves with a constant phase difference

Question 6

What type of light source produces coherent light?

Answer 6

Monochromatic (lasers)

Question 7

What is refraction?

Answer 7

A change in the speed and direction of a wave when it moves from one medium to another

Question 8

What causes refraction in visible light?

Answer 8

The difference in optical density (refractive index) between two media

Question 9

How is the refractive index defined?

Answer 9

The ratio between the speeds of light before and after it enters a different medium

Question 10

What is the refractive index of air?

Answer 10

1

Question 11

What happens to light when it enters a more optically dense material?

Answer 11

It slows down and bends toward the normal

Question 12

What is total internal reflection?

Answer 12

When light cannot refract through to another medium and is reflected back into the initial, denser medium

Question 13

What is the critical angle?

Answer 13

The angle of incidence that corresponds to a refraction angle of 90 degrees

Question 14

What is an optical fibre?

Answer 14

A filament made from a material that can transmit light, such as silica

Question 15

What surrounds the core of an optical fibre?

Answer 15

A cladding, which must have a lower refractive index than the core

Question 16

What is multimodal dispersion?

Answer 16

The phenomenon where can light travels through an optical fibre in multiple paths, leading to pulse broadening

Question 17

What does endoscopy refer to?

Answer 17

Looking inside the body for medical reasons using an endoscope

Question 18

What is diffraction?

Answer 18

The tendency of a wave to spread out as it goes around an obstacle

This property is common to all waves, similar to reflection and refraction.

Question 19

Does diffraction affect the properties of a wave?

Answer 19

No, the wavelength, frequency, period, and speed remain the same; only the direction changes.

Question 20

What happens when light passes through a very narrow slit?

Answer 20

The image appears streaky due to diffraction by both edges of the slit.

Question 21

What initial condition leads to the greatest diffraction effect when using a single slit?

Answer 21

Slit width must be approx. equal to wavelength

Question 22

What is observed on a screen when a laser passes through a single slit?

Answer 22

A large, bright central smudge and dimmer smudges on either side, known as higher orders of diffraction.

Question 23

How does the width of the bright central maximum compare to the subsidiary maxima in single-slit diffraction?

Answer 23

The bright central maximum is twice the width of the subsidiary maxima.

Question 24

What is produced in a double-slit diffraction experiment?

Answer 24

A pattern of bright and dark fringes appear, in addition to the usual diffraction pattern

Question 25

What initial condition causes the formation a bright fringe in the double-slit diffraction pattern?

Answer 25

The path length difference between the slits and the screen is equal to a whole number of wavelengths.

Question 26

What produces a dark fringe in a double-slit diffraction pattern?

Answer 26

The light from the two slits is out of phase, occurring at a half-integer number of wavelengths.

Question 27

What is fringe spacing?

Answer 27

The distance between bright fringes.

Question 28

When is the fringe spacing formula valid?

Answer 28

When the screen distance is much greater than the slit separation.

Question 29

What is a diffraction grating?

Answer 29

A tile containing many narrow slits, through which light may be shone, causing significant diffraction and interference.

Question 30

What happens to light when it passes through a diffraction grating?

Answer 30

Light from the source is almost entirely cancelled out, except in a few very specific directions where it remains visible.

Question 31

What are the locations where light can be seen known as (in experiments with diffraction gratings)?

Answer 31

These locations are known as 'orders of diffraction' and are given the symbol n.

Question 32

Why is light visible at the n=1 location?

Answer 32

The path length difference between adjacent slits and the screen is one wavelength

Question 33

How does wavelength affect diffraction?

Answer 33

Waves with a longer wavelength diffract at larger angles.

Question 34

How can the wavelength of light be calculated using diffraction gratings?

Answer 34

By measuring the angle between the central maximum and a given order of diffraction.

Question 35

What happens when white light passes through a diffraction grating?

Answer 35

Red light, with the longest wavelength, is diffracted at the largest angle, while blue light is diffracted the least. The central maximum (undiffracted light) remains white.