Ray Optics and Optical Instruments

Notes

1. Optics

Optics is a special branch of Physics that deals with light.

Parts of Optics

1. Ray Optics or Geometrical Optics
2. Wave Optics
3. Fibre Optics

Ray Optics

The study of reflection, refraction, dispersion, scattering and image formation by the lens and mirror using rays travelling in a straight line is called Ray Optics.

Wave Optics

The study of interference, diffraction and polarisation of light on the basis of wave nature is called Wave Optics.

Fibre Optics

The study of transmission of light energy through optical fibres is called Fibre Optics.

Further Parts of Ray Optics

• Light and its properties
• Rays or beam of light
• Reflection
• Mirror
• Image formation by mirrors
• Refraction
• Lens
• Image formation by lenses
• Prism
• Dispersion
• Scattering
• Optical instruments – eye, microscope and telescope

2. Light

Light is a form of radiant energy and also an electromagnetic wave. It moves with a speed of 3 × 10⁸ m/s in vacuum and creates the sensation of vision in the eyes.

Light moves with a speed of approximately 2.25 × 10⁸ m/s in water.

Properties of Light

• Light can be reflected.
• Light can be refracted.
• Light moves in a straight line. This is called the rectilinear property.
• Reflection, refraction, dispersion and scattering show the ray nature of light.
• Polarisation, diffraction and interference show the transverse nature of light.

3. Ray of Light

The path which gives the direction of light is called a ray of light.

Types of Rays

1. Visible rays
2. Infrared rays
3. Ultraviolet rays

4. Beam of Light

A bunch of rays of light is called a beam of light.

Types of Beam

1. Parallel beam
2. Converging beam
3. Diverging beam

5. Reflection of Light

Reflection of light is the phenomenon of returning back of light after striking a plane or smooth surface.

Rules of Reflection of Light

1. Angle of incidence = Angle of reflection
2. The incident ray, reflected ray and normal drawn at the point of incidence all lie in the same plane.

∠i = ∠r

Important Terms

Incident Ray: The ray coming towards the plane surface.

Reflected Ray: The returning ray after striking the plane surface.

Normal: The perpendicular at the point of incidence.

Point of Incidence: The point at which the incident ray falls.