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Question 19M.2.HL.TZ2.8a

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.2.HL.TZ2.8a
Level HL Paper 2 Time zone TZ2
Command term Deduce Question number a Adapted from N/A
a.
[Maximum mark: 3]
19M.2.HL.TZ2.8a

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.

(a)

Deduce, in W m-2, the intensity at M.

[3]

Markscheme

there is constructive interference at M

OR

the amplitude doubles at M ✔

intensity is «proportional to» amplitude2 ✔

88 «W m−2» ✔

Examiners report

This was generally well answered by those who attempted it but was the question that was most left blank. The most common mistake was the expected one of simply doubling the intensity.

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