Ray Optics and Optical Instruments

Geometric Optics

Geometric optics, or ray optics, refers to a model of optics that in terms of rays describes light propagation. Furthermore, the ray in geometric optics is an abstraction useful for approximating the paths along which the propagation of light takes place under certain circumstances. The concept of geometric optics should not be confused with the concept of physical optics, which studies the phenomena for which geometric optics is not valid.

Introduction to Geometric Optics

When it comes to geometric optics, there is no account for some optical effects like interference and diffraction. Furthermore, this simplification will turn out to be useful in practice. Moreover, it is a very good approximation when the wavelength is small in comparison to the size of structures with which the interaction of the light takes place.

Two important geometric optics examples are a reflection of light and refraction of light. Furthermore, when the reflection of a ray of light takes place by some angle by a barrier in its pathway, the rebounding of the light beam takes place and this procedure is called the reflection of light. Also, refraction of light is the procedure in which the beam of light diverges slightly from its route when it crosses from one medium to the other.

geometric optics

The Laws of Reflection in Geometric Optics

The conduct of the ray of light, whose rebounding take place by a smooth mirror, must be judged on the basis of the laws of reflection. However, one must need to understand the basic terms.

Incident ray refers to the light that is approaching a mirror. Furthermore, reflected ray refers to a beam of light whose reflection takes place by the mirror. The normal refers to the spot of reflection, the drawn perpendicular.

The angle of incidence is the angle amidst the incident ray and the normal. Furthermore, the angle of reflection refers to the angle that is amidst the reflected ray and the normal. When one confers to the laws of reflection, the angle of reflection is always equivalent to the angle of incidence.

Formulae For Geometric Optics

  1. Laws of reflection of light
  • Lying on the same plane are the incident ray, the refracted ray, and normal
  • Snells law

sin i/sin r = constant

  1. Relative refractive index 1n2= v1/v2

v= velocity of light in first medium

v= velocity of light in second medium

  1. Absolute Refractive indexn = c/v

c= velocity of light in air

v = velocity of light in given medium

  1. Lateral Shift

T sin(i-r)/cos r

5. Relative refractive index 1n2 = v1/v2

v= velocity of light in first medium

v= velocity of light in second medium

6. Absolute Refractive indexn = c/v

c= velocity of light in air

v = velocity of light in given medium

  1. Refraction through a prism

Refractive index of the prism n = [sin(A+δ/2)]/sin A/2

  1. Deviation whose production happens by a thin film d = (n-1) A

(n-1) is called the refractivity of the material

  1. Angular dispersion between two coloursAngular dispersion = (nv-nr)A

nv, nis the refractive index of violet light and red light

  1. Dispersive powerω = nv– nr/n-1
  2. Lens makers formula for thin lenses1/f = (n-1) { 1/R– 1/R2}
  3. Power of lensP = 1/f
  4. Equivalent focal length of combination of two thin lenses1/f = 1/f1+ 1/f2

FAQs For Geometric Optics

Question 1: What is meant by geometric optics?

Answer 1: Geometric optics is simply a model of optics that in terms of rays tells us about light propagation. Furthermore, geometric optics helps in the approximation of the paths along which the propagation of light takes place under certain circumstances. Moreover, the concept of geometric optics should not be confused with the concept of physical optics, the latter involves the study of the phenomena for which geometric optics is not valid.

 Question 2: Explain the refractive index of the medium in geometric optics?

Answer 2: The refractive index is denoted by the letter ‘n’. Furthermore, it is a dimensionless number that shows the radiation or light that travels via a medium. Mathematically, its expression is as follows:

n = c/v

Where,

‘v’ represents the phase velocity of light that is present in a medium, and

‘c’ indicates the speed of light that is in a vacuum.

 

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