Introduction to minimum deviation of a prism:
A prism is a transparent medium bounded by two plane surfaces inclined to each other at a suitable angle. The angle between two surfaces is known as refracting angle or angle of prism. In a prism, a ray of light suffers two refraction and the result is deviation. In other words, we say that after passing through prism the ray of light deviates through a certain angle from its original path.
Minimum Deviation of a Prism:
Look at the given diagram, here ABC is the principal section of the prism and the angle of prism is A.
A ray of light KL is incident on face AB of the prism at Ði1. It bends towards the normal NO and refracted along LM at Ðr1. The refracted ray LM is incident at Ðr2 on face AC of the prism. It bends away from the normal PO and emerges MS at angle Ði2. In passing through the prism, the ray KL suffers two refraction and finally turned through an ÐQTM = d, this is the angle of deviation.
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Calculation for the Minimum Deviation of a Prism:
In TLM, `delta` = TLM + ÐTML
`delta` = (i1 – r1) + (i2 – r2)
`delta` = (i1 + i2) - (r1 + r2) ….(1)
In D OLM, ÐO + r1 + r2 = 180° ….(2)
In quadrilateral ALOM,
ÐL + ÐM = 180°
ÐA + ÐO = 180°
Put this value in equation (2), we get
ÐO + r1 + r2 = ÐA + ÐO
r1 + r2 = ÐA ….(3)
Put this value in equation (1)
`delta` = (i1 + i2) – A ….(4)
Let n be the refractive index of the medium of prism with respect to air
n = Sin i1 / Sin r1 = i1 /r1 (when angles are small)
i1 = n r1 , Similarly i2 = n r2
Put this value in equation (4), we get
d = n(r1 + r2) – A
d = n A – A
`delta` = (n – 1)A
In case of minimum deviation of a prism, i1 = i2 = i so that r1 = r2 = r, so put these values in equation (3) and in equation (4), we get
r + r = A
r = A/2
`delta`m = (i + i) – A = 2i – A where dm is the minimum deviation angle
i = ( `delta`m + A)/2
n =
A prism is a transparent medium bounded by two plane surfaces inclined to each other at a suitable angle. The angle between two surfaces is known as refracting angle or angle of prism. In a prism, a ray of light suffers two refraction and the result is deviation. In other words, we say that after passing through prism the ray of light deviates through a certain angle from its original path.
Minimum Deviation of a Prism:
Look at the given diagram, here ABC is the principal section of the prism and the angle of prism is A.
A ray of light KL is incident on face AB of the prism at Ði1. It bends towards the normal NO and refracted along LM at Ðr1. The refracted ray LM is incident at Ðr2 on face AC of the prism. It bends away from the normal PO and emerges MS at angle Ði2. In passing through the prism, the ray KL suffers two refraction and finally turned through an ÐQTM = d, this is the angle of deviation.
Between, if you have problem on these topics college algebra problem solver, please browse expert math related websites for more help on how do you convert fractions to decimals.
Calculation for the Minimum Deviation of a Prism:
In TLM, `delta` = TLM + ÐTML
`delta` = (i1 – r1) + (i2 – r2)
`delta` = (i1 + i2) - (r1 + r2) ….(1)
In D OLM, ÐO + r1 + r2 = 180° ….(2)
In quadrilateral ALOM,
ÐL + ÐM = 180°
ÐA + ÐO = 180°
Put this value in equation (2), we get
ÐO + r1 + r2 = ÐA + ÐO
r1 + r2 = ÐA ….(3)
Put this value in equation (1)
`delta` = (i1 + i2) – A ….(4)
Let n be the refractive index of the medium of prism with respect to air
n = Sin i1 / Sin r1 = i1 /r1 (when angles are small)
i1 = n r1 , Similarly i2 = n r2
Put this value in equation (4), we get
d = n(r1 + r2) – A
d = n A – A
`delta` = (n – 1)A
In case of minimum deviation of a prism, i1 = i2 = i so that r1 = r2 = r, so put these values in equation (3) and in equation (4), we get
r + r = A
r = A/2
`delta`m = (i + i) – A = 2i – A where dm is the minimum deviation angle
i = ( `delta`m + A)/2
n =

