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Question 19M.2.HL.TZ2.b

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.HL.TZ2.b
Level HL Paper 2 Time zone TZ2
Command term Calculate Question number b Adapted from N/A
b.
[Maximum mark: 2]
19M.2.HL.TZ2.b

Monochromatic coherent light is incident on two parallel slits of negligible width a distance d apart. A screen is placed a distance D from the slits. Point M is directly opposite the midpoint of the slits.

Initially the lower slit is covered and the intensity of light at M due to the upper slit alone is 22 W m-2. The lower slit is now uncovered.

P is the first maximum of intensity on one side of M. The following data are available.

d = 0.12 mm

D = 1.5 m

Distance MP = 7.0 mm

Calculate, in nm, the wavelength λ of the light.

[2]

Markscheme

« s = λ D d ⇒ » λ = s d D / 0.12 × 10 − 3 × 7.0 × 10 − 3 1.5    ✔

λ = 560 « nm »  ✔

 

Examiners report

This was very well answered. As the question asks for the answer to be given in nm a bald answer of 560 was acceptable. Candidates could also gain credit for an answer of e.g. 5.6 x 10-7 m provided that the m was included.

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