The index of refraction, also called the refractive index, is a measurement of how much a ray of light bends as it passes through one medium and into another. If ’i’ is the angle of incidence for a ray in the vacuum (the normal is the angle formed by the incoming ray and the perpendicular to the medium’s surface), and ‘r’ is the angle of refraction(the angle between the ray in the medium and the normal).
The refractive index n is defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction ; n = sin i / sin r. The velocity of light c of a particular wavelength in empty space divided by its velocity v in a substance, or n = c/v, is the refractive index.
A vertically mounted compound microscope is known as a travelling microscope. It has a vernier scale that may be moved up and down along with the main scale. A glass slab is a substance or sheet formed of glass that is cuboidal in shape and has three dimensions: length, width, and height. It doesn’t divert or scatter the light beams that travel through it.
The incident and emergent rays originating from the glass slab are therefore parallel. Only a lateral or (sideways) shift or displacement in the direction of light is produced by the glass slab.
Required materials for the same:
The idea behind a glass slab
Due to the phenomenon of refraction, when a glass slab is placed in the air on a horizontal surface, and its bottom side is viewed from above, it appears to be elevated. The gap between this seeming bottom and the actual bottom, the apparent thickness of the slab, is determined by the top surface of the slab.
When a glass slab is put on a horizontal surface, and the bottom surface is viewed from above, it seems to be elevated owing to refraction. The distance between the apparent bottom and top of the glass slab determines the apparent thickness of the slab. The refractive index of the medium and air is calculated as follows:
n = real thickness of the slab/apparent thickness of the slab
Series of steps:
Real thickness = R3-R1
Apparent thickness = R3-R2
Refractive index n = R3 – R1/R3 – R2
The ratio R3- R1/R3- R2 determines the refractive index of the glass slab.
Major precautions to be taken
Error-Producing Sources
A normal shift is an apparent shift in the position of an object placed in one medium and observed along the normal from the other medium. A normal shift occurs when an object and an observer are in distinct media, and the object’s image appears to have been displaced from its original position.
The normal shift is determined by the thickness and refractive index of the refracting material.
The apparent shift of a ray is the perpendicular distance between the incident and emerging rays as measured by light refraction through a glass slab. When different torques exist and are balanced by the box being level on the ground, the normal force shifts.
Consider the case of a box on a frictionless surface. To balance gravity, the normal force must act through the centre of mass when it is stationary. Now, from one of the top sides, push the box sideways. Because the push is above the centre of mass, torque is created. Gravity is incapable of restoring torque. Instead, we analyse the normal force operating at a place that generates enough torque to result in zero total torque.
Metre is the SI unit for normal shift. The emergent ray changes laterally when a ray of light strikes a parallel-sided glass slab obliquely. “Lateral shift” refers to the perpendicular distance between the incident and emerging ray directions.
When an object is placed in one medium and observed through another, the observer’s image and the object are in distinct places. Note that when an object is in a denser medium, the picture shifts towards the boundary, and when the object is in a less dense medium, the image moves away from the boundary.
The following are the factors that influence apparent depth:
The refractive index of a medium is measured with a refractometer. Refractometers come in a variety of shapes and sizes, including the Abbe refractometer. The theory behind a refractometer is that light bends when it enters a different medium. The angle of refraction of light rays travelling through an unknown substance is measured with this equipment. By applying Snell’s law, this measurement, along with knowledge of the refractive index of the medium directly in contact with the unknown sample, is used to determine the refractive index of the unknown sample.
Refractive indices serve a variety of applications, but they are most commonly employed to distinguish between liquid samples. As a result, in the same way, as melting points are used to characterise solids, this physical quantity is utilised to characterise liquids. By comparing a substance’s refractive index to known literature values, this measurement can be used to identify it. Furthermore, by comparing the refractive index of a substance to that of a pure compound, refractive indices can be used to assess the purity of a chemical.
By comparing the solution’s refractive index to a standard curve, refractive indices can also be used to determine the concentration of a solute in a solution. Finally, the polarizability of a material affects refractive indices. The higher a substance’s refractive index, the more polarizable it is. As a result, knowing a substance’s refractive index is also required to compute its dipole moments.
The refractive index is affected by the following factors:
Temperature
Light’s wavelength
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