IB Physics HL C.3.10 Thin-Film Interference Question Bank

Practise IB Physics HL C.3.10 by solving phase-change, thin-film thickness, reflected-wavelength and anti-reflection problems.

[Maximum number: 4]

Monochromatic light enters the base of a plastic beaker that contains water with an oil layer floating on it. A student draws a diagram to show the directions the light takes as it passes through the layers. The student's diagram has one error at position A and one error at position B. The refractive indices of the materials are shown on the diagram.

Figure for Question C.3.10—Thin-film interference question 1 — IB Physics HL

The light is refracted at an angle of $32^{\circ}$ when it enters the plastic layer as shown.

(a)

Monochromatic light of wavelength $6.3 \times 10^{-7} \mathrm{~m}$ in air is incident from above at a normal to the oil layer. Rays on the diagram are shown at near-normal incidence for clarity. Three positions X, Y and Z are shown on the diagram.

[ 4 ]

(i)

Identify, with a reason, a position at which there is a phase change of $180^{\circ}$ .

[ 1 ]

(ii)

Determine the minimum thickness of the oil layer for which light is not reflected. State your answer to an appropriate number of significant figures.

[ 3 ]

Use of $2 d \mathrm{n}=m \lambda$ $2.1 \times 10^{-7}$ «m»

any answer to 2 s.f.

'Use of' requires a substitution
NOT just a statement of a formula

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C.3.10—Thin-film interference question 1

Question (a)

Question (i)

Question (ii)