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The bending of light as it passes from one medium to another is called refraction. The angle and wavelength at which the light enters a substance and the density of that substance determine how much the light is refracted. The bending occurs because light travels more slowly in a denser medium.

Deviation of Light by a Glass Prism and a Rectangular Glass Slab

Introduction:
When a ray of light passes from one medium to another, it undergoes a change in its direction. This phenomenon is known as refraction. The amount of deviation in the path of light depends on the refractive index of the medium through which it is passing. In this context, let's understand how a glass prism and a rectangular glass slab can produce a deviation in the path of a ray of light.

Refraction and Deviation of Light:
- Refraction occurs when light passes from one medium to another, and the speed of light changes. This change in speed causes the ray of light to bend or deviate from its original path.
- The deviation of light is determined by the refractive index of the medium. The refractive index is a measure of how much a material can change the direction of light as it passes through it.
- The refractive index of a medium is defined as the ratio of the speed of light in a vacuum to the speed of light in that medium. It is denoted by the symbol 'n'.
- When a ray of light passes from a medium with a lower refractive index to a medium with a higher refractive index, it bends towards the normal. Conversely, when it passes from a medium with a higher refractive index to a medium with a lower refractive index, it bends away from the normal.

Deviation by a Glass Prism:
- A glass prism is a transparent optical element with two triangular ends and three rectangular faces. It is made of a material that has a higher refractive index than air.
- When a ray of light enters a glass prism, it undergoes refraction at each of the two surfaces it encounters. The refraction at the first surface causes the ray to bend towards the base of the prism, and the refraction at the second surface causes it to bend away from the base.
- Due to the combined effect of these two refractions, the ray of light deviates from its original path and emerges in a different direction.

Deviation by a Rectangular Glass Slab:
- A rectangular glass slab is a transparent medium with parallel flat surfaces. It is also made of a material with a higher refractive index than air.
- When a ray of light enters a rectangular glass slab, it undergoes refraction at each of the two surfaces it encounters. The refraction at the first surface causes the ray to bend towards the normal, and the refraction at the second surface causes it to bend away from the normal.
- However, the deviation caused by the refractions at the two surfaces is equal in magnitude but opposite in direction. As a result, the ray of light emerges parallel to its original path, without any deviation.

Conclusion:
- A glass prism can produce a deviation in the path of a ray of light due to the combined effect of refractions at its surfaces.
- On the other hand, a rectangular glass slab does not produce any deviation in the path of a ray of light as the opposite deviations caused by refractions at its surfaces cancel each other out.
- Therefore, the correct answer is option 'A', which states that both a glass prism and a rectangular glass slab can produce a deviation in the path of a ray of light.