| Aim | To determine the refractive index of a glass slab using a traveling microscope. |
| Apparatus Required | Glass slab Traveling microscope Light source (such as a lamp or laser) A ruler or measuring tape A protractor or an angle measuring device A white paper or screen |
| Theory | The refractive index of a medium is defined as the ratio of the speed of light in vacuum to the speed of light in the medium. The refractive index of a glass slab can be determined by measuring the thickness of the slab and the displacement of the image of an object viewed through the slab. The displacement is caused due to the refraction of light as it passes through the glass slab. |
| Procedure | Place the glass slab on a white paper or screen. Place the traveling microscope on the opposite side of the glass slab. Adjust the height of the microscope so that the crosshairs of the microscope are at the same height as the center of the glass slab. Place a light source (such as a lamp or laser) behind the glass slab so that the light passes through the slab and illuminates the object on the other side of the glass slab. Adjust the position of the object until it is visible through the glass slab. Focus the microscope on the object and measure the distance between the crosshairs and the object on the opposite side of the glass slab. This is the apparent distance. Remove the glass slab and measure the distance between the crosshairs and the object without the glass slab. This is the actual distance. Calculate the thickness of the glass slab by subtracting the actual distance from the apparent distance. Measure the angle of incidence and angle of refraction of the light passing through the glass slab using the protractor or angle measuring device. Calculate the refractive index of the glass slab using the formula: n = sin(i) / sin(r), where n is the refractive index, i is the angle of incidence, and r is the angle of refraction. |
| Observation and Result | Observation: The image viewed through the glass slab appears to be displaced from its actual position. The amount of displacement depends on the thickness of the glass slab and the angle of incidence. The thickness of the glass slab can be measured accurately using a traveling microscope. The angle of incidence and angle of refraction can be measured using a protractor or an angle measuring device. The refractive index can be calculated using the measured values of the thickness, angle of incidence, and angle of refraction. Result: The refractive index of the glass slab can be determined accurately using the traveling microscope method. The accuracy of the measurement can be improved by taking multiple measurements and calculating the mean and standard deviation. The refractive index of the glass slab can be used to determine other optical properties of the material, such as the critical angle, total internal reflection, and the speed of light in the medium. |
