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### Course: UP Class 12 Physics>Unit 2

Lesson 5: Refraction through a prism

# Minimum deviation in prism

What causes the famous 22-degree halo around the sun? In this video let's explore the concept of minimum deviation in a prism and how that results in beautiful halo formations. Created by Mahesh Shenoy.

## Want to join the conversation?

• What does 22-degree halo mean?
• A 22° halo is an optical phenomenon that belongs to the family of ice-crystal halos. Its form is a ring with an apparent radius of approximately 22° around the Sun or Moon. When visible around the Moon, it is called a moon ring or winter halo. May be this helps you :)
• if blue light is incident at 30degree to a prism is deviated by 28degree, then choose the correct option for deviation for green light and red light at the same angle of incidence of 30degree

green red

1) 20 23

2) 25 20

3) 25 28

4) 23 28
• Option 2) 25, 20 is correct. Green light will deviate by 25 degrees and red light by 20 degrees. Violet light deviates the most and red light the least. Deviation of light decreases while going from violet to red following VIBGYOR.So, green light will deviate lesser than blue light and red light will deviate the least. Only option 2 satisfies this condition.
• is there any relation between the Minimum deviation in prism and the radius of the sun aura?
is there any ready to apply site that we can use to apply the equation and find out the Minimum deviation in prism?
dshqairat@gmail.com
• I think the possible relation bw angle of min. deviation(d) and radius of sun halo(r) is that:
tan(d)=r/s
where s=perpendicular distance from your eye to the sky.

I thought about it myself, so, please pardon if you find that it's wrong.