Physics Problem: (POST HERE)

[UXm@N]

This question 5 of CIE A-LEVELS of 9702/02/O/N/07 (PHYSICS ouc/nov. 2007)

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_w07_qp_2.pdf

"(c) State the effect, if any, on the appearance of the fringes observed on the screen when the following changes are made, separately, to the double-slit arrangement in (b).
(i) The width of each slit is increased but the separation remains constant.
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My response:
As the INTENSITY is inversely proportional to the AREA , so on increasing width of the slit(AREA) the INTENSITY decreases. As INTENSITY is directly proportional to the (AMPLITUDE)^2 so Amplitude also decreases.
Thus bright fringe becomes less bright, dark remain the same and off course there is no effect on fringe width as fringe separation remains same.

Answer in Marking Scheme:

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_w07_ms_2.pdf

(c) (i) same separation B1
bright areas brighter (1) dark areas, no change (1)
(allow ‘contrast greater’ for 1 mark if dark/light areas not discussed)
fewer fringes observed (1) any two, 1 each


What I dont understand is how bright fringe get brighter and how come there are fewer fringes observed, according to answer???

Please explain...