2.5 wave properties

Question 1

why is a laser useful in showing interference and diffraction

Answer 1

it produces monochromatic light meaning diffraction and interference can be more defined

Question 2

youngs double slit experiment

Answer 2

a single light source is directed towards two slits, which each act as a coherent light source. the light interferes constructively and destructively to create an interference pattern

Question 3

describe the interference pattern created using white light

Answer 3

a bright white central maximum with alternating spectral fringes of decreasing intensity with violet closest to the zero order and red furthest

Question 4

why does an interference pattern form when light is passed through a single slit

Answer 4

the light diffracts as it passes through the slit. where the waves are in phase, constructive interference occurs making bright fringes. where the waves are completely out of phase, destructive interference occurs making a dark fringe

Question 5

stationary waves

Answer 5

a wave which transfers no energy and whose positions of maximum ad minimum amplitude are constant

Question 6

node

Answer 6

a point on a stationary wave with 0 displacement

Question 7

antinode

Answer 7

a point on a stationary wave with maximum displacement

Question 8

conditions for stationary waves

Answer 8

same frequency, wavelength and amplitude
travelling opposite directions

Question 9

how are stationary waves produced

Answer 9

from the superposition of 2 progressive waves, travelling in opposite directions in the same plane, with the same frequency, wavelength and amplitude:
• Where the waves meet in phase, constructive interference occurs so antinodes (regions of maximum amplitude) form.
• Where the waves meet completely out of phase, destructive interference occurs and nodes (regions of no displacement) form.

Question 10

first harmonic of a stationary wave with two closed ends

Answer 10

1 node at each end and an anti node in the middle

Question 11

define coherent

Answer 11

have a fixed phase difference and the same frequency and wavelength

Question 12

Derive the formula dsin0=n2

Answer 12

1. For the first order maximum, the path difference between two adjacent rays of light is 1 wavelength. The angle between the normal to the grating and the light ray is theta.
2. A right angled triangle is formed, with side lengths d and wavelength. The upper angle is theta (the lower angle is 90-theta°).
3. For the first maximum sin theta =wavelength/d, (sin 0 = Opp/Hyp)
   rearrange to dsin =wavelength
4. Other maxima occur when the path difference between the two rays of light is n wavelength , where n is an integer, replace wavelength with n wavelength to get: d sin =n wavelength

Question 13

diffraction

Answer 13

the spreading of waves when the pass through a gap

Question 14

how did youngs double slit experiment provide evidence for the wave nature of light

Answer 14

diffraction and interference are wave properties hence the interference pattern of light has wave properties