Optics – Mirrors & Lenses

Optics – Mirrors & Lenses

• Light follows a rectilinear propagation (3 * 10⁸ m/s)
• Umbra > Point source of light > Shadow (Total dark)
• Penumbra > Extended source of light > Shadow (Partial dark)

Plane Mirror

Angle of incidence (i) = Angle of reflection (r)

Image formed on Plane mirrors

• Virtual & Erect
• Equal distance & size
• laterally inverted

Concave & Convex Mirrors

Image formed by Concave Mirror

Image formed by Convex Mirror

Distinction between a Plane, Concave & Convex Mirror

Use of Concave & Convex Mirrors

Refraction

• Velocity is higher in less denser medium
• n₂₁ = v₁/v₂ (n₂₁ > refractive index of medium 2 wrt medium 1)
• A ray of light will bend towards the normal if it is travelling from rarer to denser medium & away from the normal if it is travelling from denser to rarer medium

Few examples of refraction

• Twinkling of stars
• Sunrise & sunset (we can see the sun 2 min before the sunrise & 2 min after the sunset)
• Bottom of water filled body appears to be raised

Concave & Convex Lenses

Dispersion of light

Total Internal Reflection

• Light can not always pass through denser to rarer medium
• if the angle of incidence > critical angle, it leads to total reflection of light
• Examples : Optical fiber, Mirage effect (Usually associated with hot deserts)

Mirage Effect

• Air near desert surface is hot & which cools rapidly with height (2 different mediums density wise)
• Rays from top of trees exceeds critical angle & TIR occurs
• Observer sees tree upside down giving illusion of water
• Vice a versa if air near the ground is cold & up above hot

Rainbow

• Formed opposite of sun
• Process > Refraction & Dispersion + TIR + Refraction & Dispersion

Scattering of Light

• A molecule of a medium emits incoming light in all possible directions known as scattering (Tyndall Effect)

Blue Color Sky

• When sunlight reaches earth’s atmosphere, Blue color scatters more strongly than the red
• When this scattered color enters our eye, sky looks blue to us

Reddish Sunrise / Sunset

• Light from sun near horizon passes through thicker layers of air & travel larger distances in earth’s atmosphere before reaching our eyes.
• Blue light & shorter wavelengths scatters away soon letting longer wavelengths of red light reach our eyes

Interference of Waves

Superimposition of 2 waves of same kind which passes through same point at the same time

• Constructive interference – Same phase interference
• Destructive interference – Opposite phase interference

Example > Colors in soap bubble & oil on water in presence of white light (Alternate black & white spots in case of monochromatic light)

Diffraction

• Spreading of light through a narrow slit or aperture
• Failure of light to travel in a straight line (due to the wave nature of light)

Diffraction Grating > A device used to cause diffraction for ex. Parallel equidistant lines on glass or metals (as in CD)

Holograms > Result of Laser + Interference + Diffraction

✅ 10 Points – Importance of Optics: Mirrors & Lenses

1. Understanding image formation and vision correction.

2. Used in designing telescopes, microscopes, cameras.

3. Helps explain reflection, refraction, and total internal reflection.

4. Essential for optical instruments in medical fields.

5. Key in designing optical fiber communication systems.

6. Supports innovations in lasers and optical devices.

7. Important in understanding the working of eyes and vision defects.

8. Used in vehicle headlights, rearview mirrors, and magnifying glasses.

9. Basis for photography, filmmaking, and lighting.

10. Vital for research in astronomy and space exploration.

For more updates, explore the Physics. Feel free to share your thoughts and comments.

If you’re passionate about building a successful blogging website, check out this helpful guide at Coding Tag – How to Start a Successful Blog. It offers practical steps and expert tips to kickstart your blogging journey!