Angle of refraction snells law

In summary, when light hits a prism with an index of 1.4, the angle of refraction is 1.4*cos(theta) and the angle of incidence is 0 degrees.
  • #1
kthejohnster
23
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im having difficulty understanding how light leaves a prism mainly because I am not sure about what angles we are talking about when we say angle of refraction/incidence.
Lets say for example light hits a triangular prism leg at a 90 degree angle (incidence = 90 deg?) and the prism has index of 1.4 compared to surrounding air's 1.0 using snells law would get an angle of refraction. Now I am getting lost trying to find the angle that it strikes the hypotenuse and the angle that it leaves the prism. how would i use snells law again?
 
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  • #2
kthejohnster said:
im having difficulty understanding how light leaves a prism mainly because I am not sure about what angles we are talking about when we say angle of refraction/incidence.
Lets say for example light hits a triangular prism leg at a 90 degree angle (incidence = 90 deg?) and the prism has index of 1.4 compared to surrounding air's 1.0 using snells law would get an angle of refraction. Now I am getting lost trying to find the angle that it strikes the hypotenuse and the angle that it leaves the prism. how would i use snells law again?

All I know is that when a monochromatic ray of light (let's say) enters from medium 1 to medium 2 then ,
Refractive index of medium 2 or 1μ2 = angle of incidence in medium 1 / angle of incidence in medium 2

Representation : 1μ2= μ21
Yes , we represent refractive index of medium 2 with respect to medium 1 as 1μ2

Always remember this to avoid confusion.

angle of refraction/incidence becomes inverse refractive index.

In your case
1.4 = sin 90o/sin r

And please I cannot understand what you mean by leg angle or etc etc ? Are you taking a right angled prism ? Please give me a diagram of your question.
 
  • #3
kthejohnster said:
Lets say for example light hits a triangular prism leg at a 90 degree angle (incidence = 90 deg?) and the prism has index of 1.4 compared to surrounding air's 1.0 using snells law would get an angle of refraction. Now I am getting lost trying to find the angle that it strikes the hypotenuse and the angle that it leaves the prism. how would i use snells law again?
I assume you mean that the light hits perpendicular to the first surface. Since angles (in Snell's law) are measured from the normal, that would mean that the angle of incidence is 0°, not 90. To find the angle that the light hits the other side of the prism, you'll need to use a bit of geometry. Figure out the new angle of incidence and apply Snell's law to find the angle the light makes upon leaving the prism.
 
  • #4
Angle of incidences and refraction(and even reflection) are always measured from the normal of refracting surface(or reflecting surface)

Remember, angle of incidence, refraction and normal always lie in the same plane.

As Doc Al pointed, since the ray is perpendicular to surface, it is actually parallel to normal and therefore angle of incidence is 0 degrees.


For further calculation you will need the angle of prism and some simple applications of geometry trigonometry
 
  • #5


First of all, it's important to understand that when we talk about angles in the context of refraction, we are referring to the angle between the incident ray (incoming light) and the normal line (a line perpendicular to the surface where the light is entering). So for your example, if the light is hitting the prism leg at a 90 degree angle, the angle of incidence would also be 90 degrees.

Now, let's say the light enters the prism and travels through it, hitting the hypotenuse at a certain angle. This angle is called the angle of deviation. In order to find this angle, we can use Snell's law, which states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the indices of refraction (n1/n2). In your example, n1 would be the index of the surrounding air (1.0) and n2 would be the index of the prism (1.4).

To find the angle of refraction, we can rearrange the equation to solve for it. So if we know the angle of incidence (which is 90 degrees in your example), we can plug in the values for n1 and n2 and solve for the angle of refraction. This will give us the angle at which the light leaves the prism.

Now, if we want to find the angle at which the light strikes the hypotenuse, we can use the law of reflection, which states that the angle of incidence is equal to the angle of reflection. So the angle at which the light strikes the hypotenuse would be the same as the angle of deviation, which we already calculated using Snell's law.

I hope this explanation helps clarify the concept of angles in refraction and how to use Snell's law to find them. Keep in mind that these calculations can become more complex when dealing with different angles and indices of refraction, but the principles remain the same. It's always important to draw a diagram and label all the angles and indices of refraction to help visualize the problem and make the calculations easier.
 

Related to Angle of refraction snells law

1. What is the angle of refraction?

The angle of refraction is the angle between the refracted ray and the normal line drawn at the point of incidence on the surface of a medium.

2. What is Snell's Law?

Snell's Law, also known as the law of refraction, states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media.

3. How is Snell's Law used to calculate the angle of refraction?

To calculate the angle of refraction, we use Snell's Law formula: n1sinθ1 = n2sinθ2, where n1 and n2 are the refractive indices of the two media and θ1 and θ2 are the angles of incidence and refraction, respectively.

4. What is the relationship between the angle of incidence and the angle of refraction?

The angle of incidence and the angle of refraction are related through Snell's Law. As the angle of incidence increases, the angle of refraction also increases, but at a slower rate. This is known as the refractive index, which is a measure of how much light bends when passing through a medium.

5. How does the speed of light change when it passes through different media?

The speed of light changes when it passes through different media due to the change in the refractive index of the medium. The higher the refractive index, the slower the speed of light will be. This is what causes light to bend and create the angle of refraction according to Snell's Law.

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