AH 3.3.6 Interference by division of wavefront

Question 1

Look the diagram below which shows a point source of light (top) and an extended source of light (bottom). Copy and complete this sentence.

From an ………………………………….. source of light (a collection of many ……………… sources) we can produce a single ………………………… source by using a slit of width < or = ………… Describe and explain Young’s double-slit interference experiment

Answer 1

From an extended source (a collection of many point sources) we can produce a single point source by using a slit of width < or = λ

Question 2

a) Draw a labelled diagram showing the experimental arrangement used by Young in his famous double-slit experiment.

b) Was Young combining two separate waves or recombining a divided
single wave?

c) What name is given to this type of interference?

Answer 2

a) See the diagram below.
b) He was combining two separate waves.
c) Interfrence by division of wavefront.

Question 3

The equation Δx = λD/d is used to describe the interference pattern observed when using Young’s double-slit arrangement.

a) Define each term in this equation.
b) Find the fringe separation if monochromatic light of wavelength 600 nm is used with a grating which has 200 lines per mm. The slit-screen distance is 4.00 m.

Answer 3

a) Δx = fringe separation (on the screen)

λ = wavelength of light used

d = slit separation in grating

D = grating to screen distance

b) Δx = ?

λ = 600 x 10^-9 m

d = 1 / 200 000 = 5.00 x 10^-6 m

D = 4.00 m

Δx = λD/d

= [600 x 10^-9 x 4.00] / 5.00 x 10^-6

Δx = 0.480 m