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Question 19N.2.HL.TZ0.b(iii)

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Date November 2019 Marks available [Maximum mark: 2] Reference code 19N.2.HL.TZ0.b(iii)
Level HL Paper 2 Time zone TZ0
Command term Discuss Question number b(iii) Adapted from N/A
b(iii).
[Maximum mark: 2]
19N.2.HL.TZ0.b(iii)

The lens of an optical system is coated with a thin film of magnesium fluoride of thickness d. Monochromatic light of wavelength 656 nm in air is incident on the lens. The angle of incidence is θ. Two reflected rays, X and Y, are shown.

The following refractive indices are available.

Air                            = 1.00
Magnesium fluoride = 1.38
Lens                         = 1.58

The thickness of the magnesium fluoride film is d. For the case of normal incidence (θ = 0),

discuss a practical advantage of this arrangement.

[2]

Markscheme

reflection from «front surface of» lens eliminated/reduced
OR
energy reaching sensor increased ✔

at one wavelength ✔

NOTE: Accept reference to reduction of glare for MP1

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