Reflation and Refraction of Light

Purpose/objective:

In this activity you can investigate laws of reflection and refraction.

Equipment needed:

1. Computer 2. Paper, Pencil

Theory:

Reflection:

The law of reflection of light states that when light bounces off from a surface, the angle of reflection is always equal to angle of incidence. Additionally, incident ray, reflected ray and normal all lie in the same plane.

Refraction:

The law of refraction of light states that, when a ray of light passes from one medium to another medium, light bends towards or away from the normal. When a light ray passes from a rarer medium to the denser medium, light ray bends towards the normal. When light ray passes from denser to rare medium, it bends away from the normal.

The Snell's law for refraction is given by :

Where, is the refractive index of one medium and is the angle of incidence. Similarly, is the refractive index of another medium and is the angle of refraction.

Total Internal Reflection:

If light passes into a medium with a smaller index of refraction, the angle of refraction is larger. There is an angle of incidence for which the angle of refraction will be 90; this is called the critical angle:

If the angle of incidence is larger than this, no transmission occurs. This is called total internal reflection

Procedure

1. Go to the following website:

https://phet.colorado.edu/en/simulation/bending-light

(You can also google for "Bending of Light".)

You will see first page as shown here.

1. Click to run the program (There is a download option too, you can download it in your computer and open there too.)
2. Click on Intro. Try to understand how each icon represents. Move around and be familiar with the simulations.

1. Press the red button to turn on laser which passes from one medium to another and learn how you can move the protractor and how to measure incident angles, reflected angles and refracted angles.

REFLECTION OF LIGHT:

Top Material: Air Top Index of Refraction (n): _____________

Bottom Material: Water Bottom Index of Refraction (n): _____________

1. Flash the light at certain angle (with certain angle of incidence) so that light gets reflected and bounce back to the same medium with certain angle of reflection.
2. After you complete the predictions, you can observe using the protractor and provide the observed refracted angle.Make prediction based on law of reflection (_i= _r)

Trials	Incident Angle (	Predicted Reflected Angle (	Observed Reflected Angle(	Comments
1
2
3
4
5

1. Draw the ray diagram here for at least two different incident angles. Just focus on the incident ray and reflected ray NOT the refracted ray, we will study law of refraction later on.

REFRACTION OF LIGHT: Part 1

Top Material: Air Top Index of Refraction (n): _____________

Bottom Material: Water Bottom Index of Refraction (n): _____________

1. Flash the light at certain angle so that light gets refracted and passes from one medium to another medium. Do it for 5 different incident angles.

Use the equations

Use the equation to predict for

1. After you complete the predictions, you can observe using the protractor and provide the observed refracted angle.

Trials	Incident Angle (	Predicted Reflected Angle (	Observed Refracted Angle(	Comments
1
2
3
4
5

1. Draw the ray diagram here for at least two different incident angles.

REFRACTION OF LIGHT: Part 2

Top Material: Water Top Index of Refraction (n): _____________

Bottom Material: Glass Bottom Index of Refraction (n): _____________

1. Flash the light at certain angle so that light gets refracted and passes from one medium to another medium. Do it for 5 different incident angles.

Use the equations

Use the equation to predict for

1. After you complete the predictions, you can observe using the protractor and provide the observed refracted angle.

Trials	Incident Angle (	Predicted Reflected Angle (	Observed Refracted Angle(	Comments
1
2
3
4
5

1. Draw the ray diagram here for at least two different incident angles.

TOTAL INTERNAL REFLECTION:

Flash the light at certain angle so that light gets refracted and passes from one medium to another medium with refracted angle is90⁰.

Use the equations

Use the equation to predict for

When you plug = 90⁰, corresponding value for is called critical angle. When you increase the incident angle, the ray undergoes total internal reflection.

Predict the critical angle for the following condition and check the predicted angle using the simulation. Make sure to provide necessary screen shot here.

1. Glass - water interface ( rays pass from Glass to Water)

Predicted for critical angle = =_____________

1. Glass - air interface (rays pass from Glass to air)

Predicted for critical angle = =_____________

1. Water to air interface ( rays pass from Water to air)

Predicted for critical angle = =_____________

After you complete the predictions, you can observe using the protractor and provide the observed refracted angle.

Trials	Predicted Angle (	Observed Angle (	Comments
Glass - water interface
Glass - air interface
Water to air interface

Discussion questions: Is it possible for total internal reflection if light passes from air to Glass, why or why not? Provide answer with reasons:

Conclusions:

Write what you learned from this experiment?