Light: Reflection & ๐ก Refraction
Comprehensive Study of Light Behavior and Optical Phenomena
What is Light? ๐ก
๐ก Nature: Light is energy in form of electromagnetic radiation
- ๐ก Wave Type: Light is electromagnetic radiation
- ๐ Wavelength: Visible light has wavelengths 400-700 nm
- ๐ Nature: Light is a transverse wave
- ๐ Primary Source: Sun is the primary source of light
- ๐ Natural Light: Sun is source of natural light on earth
- ๐ฌ Study: Optics is branch of physics dealing with study of light
- โญ Star Light: Stars shine with their own light
Laws of Reflection ๐ช
Statement: The angle of incidence is equal to angle of reflection
๐ Meaning: Incident angle equals reflected angle
Statement: Incident ray, reflected ray and normal all lie in the same plane
๐ Meaning: All three rays are coplanar
๐ฏ Geometry: No ray deviates out of the plane
Spherical Mirrors ๐ช
Most common type of curved mirrors are spherical mirrors:
Shape: Curved inward (towards center)
๐ Also Called: Converging mirror
๐ฏ Uses:
- Searchlights
- Reflecting telescopes
- Magnifying purposes
๐ผ๏ธ Image: Can form real and virtual images
Shape: Curved outward (away from center)
๐ค Also Called: Diverging mirror
๐ฏ Uses:
- Rear-view mirrors in cars
- Street light lamps
- Security mirrors
๐ผ๏ธ Image: Always virtual and erect
Important Terms for Spherical Mirrors ๐
Center of reflecting surface in spherical mirror
๐ Also Called: Midpoint of spherical mirror
Center of sphere of which mirror is a part
๐ Convex: Lies behind mirror
๐ Concave: Lies in front of mirror
Radius of sphere of which mirror is a part
๐ Relation: R = 2f
Straight line passing through pole and center of curvature
Point on principal axis where reflected rays meet or appear to come from
Distance between pole and principal focus
๐ Formula: f = R/2
Additional Terms & Key Relationships ๐
- ๐ Aperture: Diameter of reflecting surface
- ๐ Object Distance (u): Distance of object from pole
- ๐ Image Distance (v): Distance of image from pole
- ๐ Key Relationship: Radius of curvature is twice the focal length (R = 2f)
- ๐ Focal Length Formula: f = R/2
- ๐ Focus Point: Light after reflection meets at focus on principal axis
- ๐ Line through Lens: Line through midpoint and principal axis is pole
Image Formation by Concave Mirror ๐
| Object Position | Image Position | Size | Nature |
|---|---|---|---|
| At infinity | At focus F | Highly diminished | Real & inverted |
| Beyond C | Between F and C | Diminished | Real & inverted |
| At C | At C | Same size | Real & inverted |
| Between C and F | Beyond C | Enlarged | Real & inverted |
| At F | At infinity | Highly enlarged | Real & inverted |
| Between P and F | Behind mirror | Enlarged | Virtual & erect |
Image Formation by Convex Mirror ๐
| Object Position | Image Position | Size | Nature |
|---|---|---|---|
| At infinity | At focus F (behind mirror) | Highly diminished | Virtual & erect |
| Between infinity and pole P | Between P and F (behind mirror) | Diminished | Virtual & erect |
- ๐ Primary Use: Used as rear-view mirrors in vehicles
- ๐ฆ Traffic Viewing: Used to see traffic behind
- โ Preferred Because: Give erect but diminished image
- ๐ก Street Lighting: Used in street light lamps
- ๐ผ๏ธ Image Nature: Always virtual and erect
Mirror Formula & Magnification ๐
Applicable for spherical mirrors in all positions of object
Relative extent to which object is magnified compared to object size
- ๐ Variables: f = focal length, v = image distance, u = object distance
- ๐ Magnification: Ratio of image height to object height
- ๐ Size Ratio: Ratio of size of image to size of object
Refraction of Light ๐
๐ Definition: Bending of light rays as it passes from one medium to another medium
๐ Alternative: Bending of light rays from its path when traveling between transparent media
- ๐ฐ Coin in Water: Coin appears at lesser depth in water
- โญ Star Twinkling: Twinkling of stars due to refraction of light
- ๐ Atmospheric Effect: Due to refraction from Earth’s atmosphere
- ๐ Sunrise Effect: Sun visible 2 minutes before actual sunrise due to refraction
- ๐ Diamond Sparkling: Sparkling of diamond due to total internal reflection
- ๐๏ธ Mirage: Mirage and looming due to total internal reflection
- ๐ง Air Bubbles: Shining of air bubble in water due to total internal reflection
Laws of Refraction ๐
Statement: Incident ray, refracted ray and normal all lie in the same plane
๐ Meaning: All three rays are coplanar
๐ฏ Geometry: Similar to reflection law
Statement: Ratio of sine of angle of incidence to sine of angle of refraction is constant
๐ Also Known As: Snell’s law of refraction
Refractive Index ๐
- ๐ Definition: Measure of how much light bends when entering a medium
- ๐ฌ๏ธ c: Speed of light in air
- ๐ง v: Speed of light in other medium
- ๐ nโ: Refractive index of the medium
- ๐ Relative Index: nโโ is refractive index of medium 2 with respect to medium 1
- ๐ Dimensionless: Refractive index has no units
Refraction by Spherical Lenses ๐
๐ Definition: Transparent materials bounded by two surfaces
๐๏ธ Also Called: Converging lens
๐ฏ Uses:
- Farsightedness correction
- Simple microscope
- Magnifying glass
โก Power: Positive power
๐ค Also Called: Diverging lens
๐ฏ Uses:
- Myopia correction
- Nearsightedness treatment
โก Power: Negative power
Image Formation by Convex Lens ๐
| Object Position | Image Position | Size | Nature |
|---|---|---|---|
| At infinity | At focus Fโ | Highly diminished | Real & inverted |
| Beyond 2Fโ | Between Fโ and 2Fโ | Diminished | Real & inverted |
| At 2Fโ | At 2Fโ | Same size | Real & inverted |
| Between Fโ and 2Fโ | Beyond 2Fโ | Enlarged | Real & inverted |
| At focus Fโ | At infinity | Infinitely large | Real & inverted |
| Between Fโ and O | Same side as object | Enlarged | Virtual & erect |
Lens Formula & Magnification ๐
Where u = object distance, v = image distance, f = focal length
Ratio of height of image to height of object
- ๐ Variables: u = object distance, v = image distance, f = focal length
- ๐ Heights: hโ = height of object, hแตข = height of image
- ๐ Magnification: Represented by m
Power of a Lens โก
โก Definition: Degree of convergence or divergence of light rays
Reciprocal of focal length is known as power
- ๐ SI Unit: Dioptre (D)
- ๐ Representation: Power represented by letter P
- โ Convex Lens: Power of convex lens is positive
- โ Concave Lens: Power of concave lens is negative
- ๐ Measurement: Power of lens measured in diopters
- ๐ Relationship: Higher power = shorter focal length
Scattering of Light ๐
๐ค๏ธ Phenomenon: Sky appears blue during clear cloudless day
๐ต Reason: Air molecules scatter blue light more than red light
๐ Process: Blue light scattered away from line of sight
๐ Phenomenon: Sky appears red and orange during sunrise/sunset
๐ด Reason: Blue light scattered out and away from line of sight
๐ Process: Red light travels longer path
- ๐ต Blue Sky Cause: Scattering of light by air molecules
- ๐ซ๏ธ Tyndall Effect: Sunlight visible through dust particles due to Tyndall effect
- ๐ No Atmosphere: Without atmosphere, sky would be black like space
- ๐ Rainbow: Rainbow caused by dispersion of sunlight
Dispersion of Light ๐
- ๐ VIBGYOR: Colors in rainbow order – Violet, Indigo, Blue, Green, Yellow, Orange, Red
- ๐บ Prism Effect: Light incident on glass prism disperses into seven color components
- ๐ฃ Maximum Deviation: Violet color deviates the most when sunlight passes through prism
- ๐ Sunlight Colors: There are 7 colors in sunlight
- ๐ Dispersion Definition: Separation of white light into seven color components
- ๐จโ๐ฌ Newton’s Discovery: Isaac Newton discovered white light consists of seven colors
- ๐ด Red Properties: Red has lowest frequency and highest wavelength
- ๐ Primary Colors: Red, Green, Blue are primary colors
- ๐ก Not Primary: Yellow is not a primary color
Applications & Instruments ๐ญ
- ๐ญ Telescope: Instrument used to see heavenly bodies
- ๐ก Photometer: Intensity of light measured with photometer
- ๐ Simple Microscope: Uses convex lens
- ๐ Magnifying Glass: Convex lens used as magnifying glass
- โ๏ธ Solar Cell: Device that converts solar energy into electrical energy
- ๐ก Photocell: Electrical energy converted into light energy inside photocell
- ๐ Sunlight Travel: Takes 8 minutes 20 seconds (500 seconds) for sunlight to reach Earth
- ๐ Light Year: Light year is measure of distance
Eye Defects & Corrections ๐๏ธ
๐ Correction: Person suffering from myopia uses concave lens
๐๏ธ Problem: Cannot see distant objects clearly
๐ Correction: Person suffering from hypermetropia uses convex lens
๐๏ธ Problem: Cannot see near objects clearly
๐๏ธ Defect: Cannot simultaneously focus on horizontal and vertical lines
๐ Correction: Corrected with cylindrical lens
Important Points – Part 1 ๐
Important Points – Part 2 ๐
Important Points – Part 3 ๐
Important Points – Part 4 ๐
Review & Summary ๐
- ๐ก Light: Electromagnetic radiation, 3ร10โธ m/s, 400-700 nm wavelength
- ๐ช Reflection Laws: โ i = โ r, all rays coplanar
- ๐ Mirrors: Concave (converging), Convex (diverging), Formula: 1/f = 1/v + 1/u
- ๐ Refraction: Light bending between media, Snell’s law: sin i/sin r = constant
- ๐ Lenses: Convex (converging, +ve power), Concave (diverging, -ve power)
- โก Power: P = 1/f, Unit: Dioptre (D)
- ๐ Dispersion: VIBGYOR, Violet deviates most, Newton’s discovery
- ๐ต Scattering: Blue sky, red sunset, Tyndall effect
- ๐๏ธ Eye Defects: Myopia (concave), Hypermetropia (convex), Astigmatism (cylindrical)