Optics

Question 1

In the Young’s slit experiment, light behaves as a wave.

EXPLAIN HOW BRIGHT FRINGES ARE FORMED.

Answer 1

• Superposition of waves from two slits
• Diffraction patterns from both slits overlap and interfere constructively
• Constructive interference/reinforcement takes place at the bright fringes. Peaks meet peaks, troughs meet troughs
• Waves from each slit meet in phase, path difference=nλ

Question 2

WHAT IS MEANT BY COHERENT SOURCES

Answer 2

Constant phase relationship/difference, and same frequency/wavelength

Question 3

EXPAIN HOW THE USE OF SINGLE SLIT IN THE ARANGEMENT MAKES THE LIGHT FROM THE TWO SLITS SUFFICIENTLY COHERENT FOR FRINGES TO BE OBSERVED

Answer 3

The single slit acts as a single source diffracting light to both slits

Question 4

A scientist carries out the Young’s double slit experiment using a laser which emits violet light of wavelength 405nm. The separation of the slits is 5.00x10^-5.
Using a metre ruler, the scientist measures the separation of 2 adjacent bright fringes in the central region of the pattern to be 4mm.
Calculate the distance between the double slits and the screen using w=λD/s

Answer 4

w=λD/s

4x10^-3=(405x10^-9)xD/(405x10^-9)
(4x10^-3)(5x10^-5)/(405x10^-9) = D
0.49m=D

Question 5

Describe the change to the pattern on the screen when the violet laser is replaced with a green laser.
Assume that the brightness of the central maximum is the same for both

Answer 5

Fringes further apart, fringe pattern is wider