To Verify The Laws Of Refraction And Determine The Refractive Index Of The Glass Slab. | Grade Xi

APPARATUS REQUIRED:

• Glass slab
• Protractor
• Drawing pins or thumbtacks
• White card or sheet of paper
• Pencil or pen
• Ruler
• Light source (e.g., LED lamp or laser pointer)
• 
  

CHEMICALS REQUIRED (if necessary):

None

THEORY:

When light travels from one medium to another, it changes direction due to refraction. The angle of refraction depends on the refractive index of the medium, which is a measure of how much light is bent when passing from one medium to another. The refractive index of a material is calculated using Snell's law:

n = sin(i) / sin(r)

where:

• n is the refractive index
• i is the angle of incidence (the angle between the incident ray and the normal to the surface)
• r is the angle of refraction (the angle between the refracted ray and the normal to the surface)

In this experiment, we will verify the laws of refraction and determine the refractive index of a glass slab using a simple setup. We will measure the angles of incidence and refraction of light passing through the glass slab and use Snell's law to calculate the refractive index.

PROCESS

1. Place the glass slab on a white card or sheet of paper.
2. Mark the center of the glass slab with a pencil or pen.
3. Draw a normal line perpendicular to the surface of the glass slab at the marked center.
4. Place a light source (e.g., LED lamp or laser pointer) on one side of the glass slab, ensuring the light beam is perpendicular to the normal line.
5. Mark the point where the incident ray strikes the glass slab.
6. Place a drawing pin or thumbtack at the point where the incident ray strikes the glass slab.
7. Mark the point where the refracted ray exits the glass slab.
8. Place a drawing pin or thumbtack at the point where the refracted ray exits the glass slab.
9. Use a protractor to measure the angle of incidence (i) and the angle of refraction (r).
10. Record your measurements in an observation table.
11. Repeat steps 5 to 10 for different angles of incidence.

OBSERVATIONS:

Trial	Angle of Incidence (i)	Angle of Refraction (r)
1	30°	20°
2	45°	28°
3	60°	36°
4	75°	43°

OBSERVATION TABLE:

Trial	Angle of Incidence (i)	Angle of Refraction (r)	sin(i)	sin(r)	n = sin(i) / sin(r)
1	30°	20°	0.5	0.342	1.46
2	45°	28°	0.707	0.469	1.5
3	60°	36°	0.866	0.588	1.47
4	75°	43°	0.966	0.682	1.42

CALCULATION:

Use Snell's law to calculate the refractive index (n) of the glass slab for each trial:

n = sin(i) / sin(r)

For example, for trial 1:

n = sin(30°) / sin(20°) = 1.46

RESULTS:

• The refractive index of the glass slab was found to be approximately 1.46, which is consistent with typical values for glass.
• The laws of refraction were verified, as the ratio of sin(i) to sin(r) remained constant for different angles of incidence.

PRECAUTIONS:

• Handle the glass slab carefully to avoid breaking it.
• Ensure that the light beam is perpendicular to the surface of the glass slab.
• Mark the points of incidence and refraction accurately using drawing pins or thumbtacks.
• Use a protractor to measure the angles of incidence and refraction accurately.