Wavefront is defined as the locus of all the points in space that reach a particular distance by a propagating wave at the same instant.
A wave front is defined as a surface of constant phase.
Definition: Ray Optics
The branch of optics that is based on rectilinear propagation of light and deals with mirrors, lenses, reflection, refraction, etc. is called ray optics.
Definition: Wave Optics
The branch of optics that considers light as a wave which can bend around objects, diffract and interfere, etc. is called wave optics.
Definition: Electromagnetic Wave (Maxwell)
Coupled time-varying electric and magnetic fields that propagate in space are called electromagnetic waves.
Definition: Polarisation
The phenomenon that is based on the fact that light waves are transverse electromagnetic waves is called polarisation.
Definition: Wavefront
A wavefront is a surface of constant phase.
Definition: Spherical Wave
If a point source emits waves uniformly in all directions, the locus of points which have the same amplitude and vibrate in the same phase is a sphere. This is known as a spherical wave.
Definition: Plane Wave
At a large distance from the source, a small portion of the spherical wave can be considered as a plane. This is known as a plane wave.
Definition: Polaroid
A Polaroid is a thin film of ultramicroscopic crystals used to produce plane-polarised light.
Definition: Plane of Vibration
The plane of vibration is the plane in which the electric field vector \[\vec{E}\] vibrates or oscillates.
Definition: Linearly Polarised Wave (Plane Polarised Wave)
A wave in which the electric field vectors are confined in one plane and are parallel to a unique direction is called a linearly polarised wave or plane polarised wave.
Definition: Transverse Wave
A transverse wave is one in which the displacement of particles is perpendicular to the direction of propagation of the wave.
Definition: Polarisation of Light
Polarisation is the phenomenon of restricting the vibration of a light wave to a particular plane perpendicular to the direction of propagation of the wave, or confining the electric vector vibrations to one direction perpendicular to the direction of propagation.
Definition: Plane of Polarisation
The plane of polarisation is the plane in which vibrations are present — it is perpendicular to the plane of vibration and contains the direction of propagation.
Definition: Unpolarised Wave
An unpolarised wave is one in which the plane of vibration changes randomly in very short time intervals.
Definition: Wave Interference
The phenomenon that occurs when two waves meet while travelling along the same medium is called wave interference.
Definition: Interference of Light
The phenomenon of redistribution of energy on account of superposition of light waves from two coherent sources is called interference of light.
Definition: Constructive Interference
The points of maximum intensity in the regions of superposition of waves are said to be in constructive interference.
Definition: Destructive Interference
The points of minimum intensity in the regions of superposition of waves are said to be in destructive interference.
Definition: Diffraction
Diffraction is the phenomenon of bending of light (or any wave) around the corners or edges of an obstacle or aperture, causing it to spread into the geometrical shadow region and produce alternate dark and bright regions.
Definition: Numerical Aperture (N.A.)
The quantity μ sin θ, where μμ is the refractive index of the medium between the object and the objective, is called the numerical aperture (N.A.) of the objective of the microscope.
Definition: Resolving Power of Telescope
The reciprocal of the least angular separation between the objects that are just resolved is called the resolving power of the telescope.
Definition: Resolving Power (Mathematical)
The reciprocal of the limit of resolution is called its resolving power.
Definition: Limit of Resolution
The minimum distance of separation between two objects when they can be observed as separate by an optical instrument is called the limit of resolution of that instrument.
Definition: Resolving Power of an Optical Instrument
The ability of an optical instrument to produce distinctly separate images of two objects very close to each other is called the resolving power of the instrument.
Definition: Fraunhofer Diffraction
Diffraction observed when the source and screen are at large distances from the diffracting element, so that the incident wavefront is plane.
Definition: Ray of Light
- The path along which light travels is called a ray of light.
- A ray is defined as the path of energy propagation in the limit of wavelength tending to zero.
Definition: Ray Optics or Geometrical Optics
- The study of optical phenomena under the assumption that it travels in a straight line as a ray is called ray optics or geometrical optics, as geometry is used in this study.
- The branch of optics in which one completely neglects the finiteness of the wavelength is called geometrical optics.
Definition: Polarization by Scattering
Polarisation by scattering is the phenomenon in which unpolarized light becomes partially or completely plane polarised when it is scattered by small particles such as air molecules or dust particles.
Definition: Wave Optics
The branch of optics which uses the wave nature of light to explain the optical phenomena is called wave optics.
Definition: Plane of Vibration
The plane containing the electric field vectors of plane polarized light is called the plane of vibration.
Definition: Plane Polarized Light
Light in which the electric field vectors vibrate only in one particular direction perpendicular to the direction of propagation.
Definition: Polarizer
A material that allows only those light waves to pass whose electric field is along a particular direction (polarizing axis).
Defintiion: Diffraction of Light
Diffraction of light is the phenomenon in which light spreads into the geometrical shadow region when it passes around the edges of an obstacle or through a narrow aperture whose size is comparable to its wavelength.
Definition: Plane of Polarization
The plane perpendicular to the plane of the vibration and the electric field vector is called plane of polarization.
Definition: Unpolarized Light
Light in which the electric field vectors vibrate in all possible directions perpendicular to the direction of propagation.
Definition: Fresnel Diffraction
Diffraction observed when the source or screen (or both) are at finite distances from the obstacle, and the incident wavefront is spherical or cylindrical.
Definition: Interference
Interference is the phenomenon in which the intensity of light (or any wave) at a point becomes non-uniform due to the superposition of two or more coherent waves, resulting in regions of constructive and destructive interference.
Definition: Limit of Resolution
The minimum visual angle between two objects that can be just resolved by an instrument is called the limit of resolution.
Definition: Resolving Power of Telescope
The resolving power of a telescope is then defined as the reciprocal of the least angular separation between the objects that are just resolved.
Definition: Resolving Power
The ability of an optical instrument to distinguish two closely spaced objects as separate and distinct is called its resolving power.
Formula: Resultant Amplitude
When two waves of amplitudes a1 and a2 interfere at a point where phase difference is ϕ, the resultant amplitude is:
\[A^2=a_1^2+a_2^2+2a_1a_2\cos\phi\]
Formula: Resultant Intensity
I = I1 + I2 + 2\[\sqrt {I_1I_2}\] ⋅ cos ϕ
When I1 = I2 = I0:
I = \[2I_0(1+\cos\phi)=4I_0\cos^2\left(\frac{\phi}{2}\right)\]
Formula: Ratio of Maximum to Minimum Intensity
\[\frac{I_{\max}}{I_{\min}}=\left(\frac{a_1+a_2}{a_1-a_2}\right)^2=\left(\frac{\sqrt{I_1}+\sqrt{I_2}}{\sqrt{I_1}-\sqrt{I_2}}\right)^2\]
Formula: Resolving Power
R.P. = \[\frac {1}{\text {Limit of resolution}}\]
Formula: Resolving Power of Microscope
R.P. = \[\frac {1}{d}\] = \[\frac{2\mu\sin\theta}{\lambda}\]
where μ sin θ is the Numerical Aperture (N.A.) of the objective.
Formula: Resolving Power of Telescope
R.P. = \[\frac{1}{d\theta}=\frac{D}{1.22\lambda}\]
Formula: Fraunhofer Diffraction at a Single Slit
\[a\sin\theta=\pm\left(n+\frac{1}{2}\right)\lambda\]
Formula: Width of the Central Bright Fringe
\[W_{c}=2y_{1d}=2W=2\left(\frac{\lambda D}{a}\right)\]
