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## Physics library

### Course: Physics library>Unit 15

Lesson 1: Reflection and refraction

# Snell's law example 2

Snell's Law Example 2. Created by Sal Khan.

## Want to join the conversation?

• So we have the distance away where the light will actually hit the bottom of the pool, but my question is: what distance from the observer will the light appear to hit the bottom of the pool?
• Basic Pythagoras Theorem, you know the distance of the observer to the bottom of the pool which is (1.7+3) and you found the distance of the of the laser beam which is
So you can connect the observes point to the laser point and that will be your 11.2m hypothenuse. So Hypothenuse square = (11.2m)squared + (4.7m) squared.
Answer: 125.44 + 22.09 = 147.53
• Hi Sal, I am a sonography student and the physics of sound is extremely important to our practice (for obvious reasons). We are learning a lot about refraction and Snell's law currently. Could you give some examples of Snell's law relating to sound traveling through different densities of tissue mediums as opposed to light traveling through different mediums? The average propagation speed of sound through soft tissues (which is the majority of our practice) is 1540m/s or 1.54mm/microsecond. Lung is 500m/s, blood is 1560m/s, adipose is 1450m/s, muscle is 1600m/s, tendon is 1700m/s and bone is 3500m/s. Thanks for your help if you decide to make some more videos! These videos are great!
• Any medium which causes the speed of a wave to change will result in refraction, whether it be light, sound, water, etc... This is due to the boundary condition that the energy of the wave be conserved when the wave transitions from one medium to another.
• Why does speed of light slow down when it passes in a medium, be it glass or water no medium in specific..??
• Due to increase/decrease in the interaction between the particles present in the medium..!!
• Why is sine function taken in snell's law?
• This is because the operation needed to solve the triangle created by the normal and ray of light is opposite over hypotenuse which is performed by the function sine.

Good question
• I'm having difficulty in understanding Snell's Law. If anyone can explain it in simple words, It will be very nice.
(1 vote)
• Whenever the speed of light changes, the direction the light is moving will change.
• Why is snell's law the way it is? I mean how did snell bought up his law?
• Just to confirm, the correct answer with the right number of significant figures would be 11.2m right?
• Yes. At , Sal says that using significant figures 11.18 would round to 11.2, implicitly applying the additive rules for significant figures to respect the location of the decimal point.
• what will happen when a handful salt is put into a glass of water?
is there any change in it?
(1 vote)
• The salt will increase the optical density of water.