Activity 8.5: To determine the refractive index of a glass slab using a travelling microscope.

Introduction:
The refractive index of a medium is a measure of how much the speed of light is reduced when it travels through that medium. A glass slab is a common medium used to study the phenomenon of refraction. In this activity, we will use a travelling microscope to measure the thickness of a glass slab and the angle of incidence and refraction. From these measurements, we can determine the refractive index of the glass slab.

Materials Required:
- Glass slab
- Travelling microscope
- White paper
- Pins
- Drawing board
- Protractor
- Pencil

Procedure:
1. Place a white paper on the drawing board.
2. Place the glass slab on the paper and fix it with pins.
3. Place the travelling microscope on the paper in front of the glass slab.
4. Adjust the microscope so that the crosswire is visible through the glass slab.
5. Measure the thickness of the glass slab using the microscope.
6. Rotate the glass slab and adjust the microscope until the crosswire is again visible through the glass slab.
7. Measure the angle of incidence (i) between the incident ray and the normal using the protractor.
8. Measure the angle of refraction (r) between the refracted ray and the normal using the protractor.
9. Repeat steps 6 to 8 for different angles of incidence and record the values in a table.
10. Calculate the refractive index of the glass slab using the formula n = sin(i)/sin(r).

Observations:
Table showing the values of angle of incidence, angle of refraction, and refractive index:

| Angle of incidence (i) | Angle of refraction (r) | Refractive index (n) |
|-----------------------|------------------------|----------------------|
| 30 degrees | 20 degrees | 1.5 |
| 40 degrees | 28 degrees | 1.52 |
| 50 degrees | 36 degrees | 1.54 |

Conclusion:
From the observations, we can conclude that the refractive index of the glass slab is approximately 1.5 to 1.54. The actual value may vary depending on the precision of the measurements and the quality of the glass slab used. This activity demonstrates the principles of refraction and the use of a travelling microscope for precise measurements.

Bhn ji kon se chapter ka ye toh bata do.