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When a ray of monochromatic light is made incident on an equilateral prism at an angle of 48° 52', the angle of emergence is 50° 53'. Calculate the value of the angle of deviation.

Asked in GSEB Board March 2020 (old course) · Deviation and minimum deviation

• (1) 39° 45'
• (2) 39° 52'
• (3) 39° 25'
• (4) 39° 10'

Step-by-step solution

Why the other options are wrong

• (2) comes from keeps the 52' of the angle of incidence instead of combining the two minute parts. It is 52'+53'=105'=1° 45' that produces the 45'.
• (3) No sum of 52' and 53' gives 25'. Sanity check: 48° 52'+50° 53'=99° 45', and 99° 45'-60°=39° 45'.
• (4) No route gives 10'. Subtracting the minute parts, 53'-52'=1', would give 39° 01'; the two must be added, not differenced.

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