Graduate Level intermediate Physics Light Sound Optics Waves Reflection Refraction
Complete notes on reflection, refraction, lenses, mirrors, sound waves, and Doppler effect for Kerala PSC graduate level exams.
Complete notes on reflection, refraction, lenses, mirrors, sound waves, and Doppler effect for Kerala PSC graduate level exams.
#Physics
#Light
#Sound
#Optics
#Waves
#Reflection
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Light and Sound are consistently tested in Kerala PSC Science sections. Questions focus on mirror/lens properties, optical phenomena, and sound-related concepts. Expect 2-3 questions per paper.
Nature of Light
Property Details Nature Electromagnetic wave (also behaves as particle — photon); wave-particle duality Speed in vacuum 3 x 10^8 m/s (approximately 3 lakh km/s) Speed in medium Slower than vacuum; slowest in denser medium Does not require Medium for propagation (travels through vacuum) Discovered wave nature Christian Huygens (wave theory); Thomas Young (double-slit experiment proved it) Discovered particle nature Albert Einstein (photoelectric effect, 1905) Electromagnetic spectrum Radio waves - Microwaves - Infrared - Visible light - UV - X-rays - Gamma rays (increasing frequency)
Reflection of Light
Law/Concept Details First Law Incident ray, reflected ray, and normal all lie in the same plane Second Law Angle of incidence = Angle of reflection Regular reflection From smooth surfaces (mirror) — clear image Diffuse/Irregular reflection From rough surfaces — scattered light, no clear image
Mirrors
Types of Mirrors
Type Shape Uses Plane Mirror Flat Dressing tables, periscopes; image is virtual, erect, same size, laterally inverted Concave Mirror Curves inward (converging) Shaving mirrors, torch reflectors, headlights, dental mirrors, solar furnaces Convex Mirror Curves outward (diverging) Rear-view mirrors in vehicles (wider field of view); image always virtual, erect, diminished
Object Position Image Position Nature of Image At infinity At Focus (F) Real, inverted, point-sized Beyond C (Centre of curvature) Between F and C Real, inverted, diminished At C At C Real, inverted, same size Between F and C Beyond C Real, inverted, magnified At F At infinity Real, inverted, highly magnified Between F and Pole Behind mirror Virtual, erect, magnified
Term Symbol Definition Focal length f Distance from pole to focus (f = R/2) Radius of curvature R Distance from pole to centre of curvature Mirror formula 1/v + 1/u = 1/f v = image distance, u = object distance Magnification m = -v/u Negative = inverted; positive = erect
Refraction of Light
Concept Details Definition Bending of light when it passes from one medium to another Cause Change in speed of light between media Denser to rarer Light bends away from normal (speed increases) Rarer to denser Light bends towards normal (speed decreases) Snell’s Law n1 sin(i) = n2 sin(r); where n = refractive index Refractive index Ratio of speed of light in vacuum to speed in medium (n = c/v)
Refractive Indices (approximate)
Medium Refractive Index Vacuum 1.00 Air 1.0003 (approximately 1) Water 1.33 Glass 1.50 (varies by type) Diamond 2.42
Phenomena Due to Refraction
Phenomenon Explanation Twinkling of stars Atmospheric refraction — light passes through layers of different density Apparent position of stars Stars appear slightly higher than actual position due to atmospheric refraction Early sunrise and delayed sunset Sun visible about 2 minutes before actual sunrise due to atmospheric refraction Pool appears shallow Light bends away from normal as it exits water; bottom appears raised Mirage Total internal reflection of light in hot air layers near ground Rainbow Dispersion + internal reflection + refraction in water droplets Broken pencil in water Refraction at water-air interface
Total Internal Reflection
Concept Details Condition 1 Light must travel from denser to rarer medium Condition 2 Angle of incidence must be greater than critical angle Critical angle Angle of incidence at which angle of refraction = 90 degrees Applications Optical fibre, diamond sparkle, mirage, prism binoculars Diamond sparkle High refractive index (2.42) means small critical angle (24.4 degrees) — more total internal reflection
Lenses
Type Shape Nature Convex (Converging) Thicker in middle Converges light rays; used in magnifying glass, camera, human eye, microscope, telescope Concave (Diverging) Thinner in middle Diverges light rays; used to correct myopia (short-sightedness); image always virtual, erect, diminished
Formula Details Lens formula 1/v - 1/u = 1/f Power of lens P = 1/f (in metres); unit = Dioptre (D) Convex lens power Positive Concave lens power Negative Magnification m = v/u = h’/h
Dispersion of Light
Concept Details Definition Splitting of white light into 7 colours by a prism Colours (VIBGYOR) Violet, Indigo, Blue, Green, Yellow, Orange, Red Most deviated Violet (shortest wavelength, highest frequency) Least deviated Red (longest wavelength, lowest frequency) Rainbow Natural dispersion; primary rainbow — red outside, violet inside; secondary — reversed Recombination Newton’s disc (spinning disc with 7 colours appears white)
Defects of Vision
Defect Problem Corrected By Myopia (Short-sightedness) Cannot see distant objects; image forms before retina Concave lens Hypermetropia (Long-sightedness) Cannot see near objects; image forms behind retina Convex lens Presbyopia Age-related; cannot see near objects Bifocal lens Astigmatism Uneven cornea curvature; blurred vision Cylindrical lens
Sound
Nature of Sound
Property Details Type Mechanical wave (requires medium) Nature Longitudinal wave (compressions and rarefactions) Cannot travel through Vacuum Speed in air (20 C) 343 m/s (approximately) Speed order Solid (fastest) then Liquid then Gas (slowest) Speed in water About 1500 m/s Speed in steel About 5000 m/s Frequency range (human) 20 Hz to 20,000 Hz (audible range)
Properties of Sound Waves
Property Details Pitch Related to frequency — higher frequency = higher pitch Loudness Related to amplitude — larger amplitude = louder sound Quality/Timbre Distinguishes same note played on different instruments; related to waveform Intensity Sound energy per unit area per unit time; unit = W/m^2 Loudness unit Decibel (dB); threshold of hearing = 0 dB; normal conversation = 60 dB; pain threshold = 120 dB
Types of Sound by Frequency
Type Frequency Range Examples Infrasonic Below 20 Hz Earthquakes, whale communication, volcanic eruptions Audible (Sonic) 20 Hz to 20,000 Hz Speech, music, everyday sounds Ultrasonic Above 20,000 Hz Bat navigation (echolocation), SONAR, medical ultrasonography, cleaning jewellery
Echo
Concept Details Definition Repetition of sound due to reflection from a surface Minimum distance 17.2 metres (at 20 C in air) — for distinct echo; based on persistence of sound in ear (0.1 seconds) Reverberation Multiple reflections of sound in enclosed space; persistence of sound Applications Stethoscope, megaphone, ear trumpet use reflection of sound
Doppler Effect
Concept Details Definition Apparent change in frequency of sound when source and observer are in relative motion Source approaches Frequency appears to increase (higher pitch); wavelength decreases Source recedes Frequency appears to decrease (lower pitch); wavelength increases Everyday example Ambulance siren — higher pitch approaching, lower pitch moving away Applications RADAR speed guns, SONAR, measuring star velocities (red shift/blue shift), medical Doppler ultrasound Not applicable when Source and observer both stationary relative to each other Light analogy Red shift (receding — lower frequency); Blue shift (approaching — higher frequency)
SONAR
Fact Details Full form Sound Navigation and Ranging Uses Detecting underwater objects (submarines, depth of ocean, fish shoals) Principle Ultrasonic waves sent; echo received; distance = (speed x time) / 2 Invented Paul Langevin (1917, during World War I)
Quick Recall — PSC Favourites
Question Answer Speed of light in vacuum? 3 x 10^8 m/s Speed of sound in air? 343 m/s (approximately) Sound travels fastest in? Solids Human audible range? 20 Hz to 20,000 Hz Myopia corrected by? Concave lens Hypermetropia corrected by? Convex lens Rear-view mirror type? Convex mirror Shaving mirror type? Concave mirror Rainbow is caused by? Dispersion + total internal reflection + refraction VIBGYOR — most deviated colour? Violet Least deviated colour? Red Doppler effect for approaching source? Higher pitch (increased frequency) SONAR uses which waves? Ultrasonic waves Minimum distance for echo? 17.2 metres Optical fibre works on? Total internal reflection Twinkling of stars due to? Atmospheric refraction Refractive index of diamond? 2.42 Unit of power of lens? Dioptre (D)
Light and Sound are consistently tested in Kerala PSC Science sections. Questions focus on mirror/lens properties, optical phenomena, and sound-related concepts. Expect 2-3 questions per paper.
Nature of Light
Property Details Nature Electromagnetic wave (also behaves as particle — photon); wave-particle duality Speed in vacuum 3 x 10^8 m/s (approximately 3 lakh km/s) Speed in medium Slower than vacuum; slowest in denser medium Does not require Medium for propagation (travels through vacuum) Discovered wave nature Christian Huygens (wave theory); Thomas Young (double-slit experiment proved it) Discovered particle nature Albert Einstein (photoelectric effect, 1905) Electromagnetic spectrum Radio waves - Microwaves - Infrared - Visible light - UV - X-rays - Gamma rays (increasing frequency)
Reflection of Light
Law/Concept Details First Law Incident ray, reflected ray, and normal all lie in the same plane Second Law Angle of incidence = Angle of reflection Regular reflection From smooth surfaces (mirror) — clear image Diffuse/Irregular reflection From rough surfaces — scattered light, no clear image
Mirrors
Types of Mirrors
Type Shape Uses Plane Mirror Flat Dressing tables, periscopes; image is virtual, erect, same size, laterally inverted Concave Mirror Curves inward (converging) Shaving mirrors, torch reflectors, headlights, dental mirrors, solar furnaces Convex Mirror Curves outward (diverging) Rear-view mirrors in vehicles (wider field of view); image always virtual, erect, diminished
Object Position Image Position Nature of Image At infinity At Focus (F) Real, inverted, point-sized Beyond C (Centre of curvature) Between F and C Real, inverted, diminished At C At C Real, inverted, same size Between F and C Beyond C Real, inverted, magnified At F At infinity Real, inverted, highly magnified Between F and Pole Behind mirror Virtual, erect, magnified
Term Symbol Definition Focal length f Distance from pole to focus (f = R/2) Radius of curvature R Distance from pole to centre of curvature Mirror formula 1/v + 1/u = 1/f v = image distance, u = object distance Magnification m = -v/u Negative = inverted; positive = erect
Refraction of Light
Concept Details Definition Bending of light when it passes from one medium to another Cause Change in speed of light between media Denser to rarer Light bends away from normal (speed increases) Rarer to denser Light bends towards normal (speed decreases) Snell’s Law n1 sin(i) = n2 sin(r); where n = refractive index Refractive index Ratio of speed of light in vacuum to speed in medium (n = c/v)
Refractive Indices (approximate)
Medium Refractive Index Vacuum 1.00 Air 1.0003 (approximately 1) Water 1.33 Glass 1.50 (varies by type) Diamond 2.42
Phenomena Due to Refraction
Phenomenon Explanation Twinkling of stars Atmospheric refraction — light passes through layers of different density Apparent position of stars Stars appear slightly higher than actual position due to atmospheric refraction Early sunrise and delayed sunset Sun visible about 2 minutes before actual sunrise due to atmospheric refraction Pool appears shallow Light bends away from normal as it exits water; bottom appears raised Mirage Total internal reflection of light in hot air layers near ground Rainbow Dispersion + internal reflection + refraction in water droplets Broken pencil in water Refraction at water-air interface
Total Internal Reflection
Concept Details Condition 1 Light must travel from denser to rarer medium Condition 2 Angle of incidence must be greater than critical angle Critical angle Angle of incidence at which angle of refraction = 90 degrees Applications Optical fibre, diamond sparkle, mirage, prism binoculars Diamond sparkle High refractive index (2.42) means small critical angle (24.4 degrees) — more total internal reflection
Lenses
Type Shape Nature Convex (Converging) Thicker in middle Converges light rays; used in magnifying glass, camera, human eye, microscope, telescope Concave (Diverging) Thinner in middle Diverges light rays; used to correct myopia (short-sightedness); image always virtual, erect, diminished
Formula Details Lens formula 1/v - 1/u = 1/f Power of lens P = 1/f (in metres); unit = Dioptre (D) Convex lens power Positive Concave lens power Negative Magnification m = v/u = h’/h
Dispersion of Light
Concept Details Definition Splitting of white light into 7 colours by a prism Colours (VIBGYOR) Violet, Indigo, Blue, Green, Yellow, Orange, Red Most deviated Violet (shortest wavelength, highest frequency) Least deviated Red (longest wavelength, lowest frequency) Rainbow Natural dispersion; primary rainbow — red outside, violet inside; secondary — reversed Recombination Newton’s disc (spinning disc with 7 colours appears white)
Defects of Vision
Defect Problem Corrected By Myopia (Short-sightedness) Cannot see distant objects; image forms before retina Concave lens Hypermetropia (Long-sightedness) Cannot see near objects; image forms behind retina Convex lens Presbyopia Age-related; cannot see near objects Bifocal lens Astigmatism Uneven cornea curvature; blurred vision Cylindrical lens
Sound
Nature of Sound
Property Details Type Mechanical wave (requires medium) Nature Longitudinal wave (compressions and rarefactions) Cannot travel through Vacuum Speed in air (20 C) 343 m/s (approximately) Speed order Solid (fastest) then Liquid then Gas (slowest) Speed in water About 1500 m/s Speed in steel About 5000 m/s Frequency range (human) 20 Hz to 20,000 Hz (audible range)
Properties of Sound Waves
Property Details Pitch Related to frequency — higher frequency = higher pitch Loudness Related to amplitude — larger amplitude = louder sound Quality/Timbre Distinguishes same note played on different instruments; related to waveform Intensity Sound energy per unit area per unit time; unit = W/m^2 Loudness unit Decibel (dB); threshold of hearing = 0 dB; normal conversation = 60 dB; pain threshold = 120 dB
Types of Sound by Frequency
Type Frequency Range Examples Infrasonic Below 20 Hz Earthquakes, whale communication, volcanic eruptions Audible (Sonic) 20 Hz to 20,000 Hz Speech, music, everyday sounds Ultrasonic Above 20,000 Hz Bat navigation (echolocation), SONAR, medical ultrasonography, cleaning jewellery
Echo
Concept Details Definition Repetition of sound due to reflection from a surface Minimum distance 17.2 metres (at 20 C in air) — for distinct echo; based on persistence of sound in ear (0.1 seconds) Reverberation Multiple reflections of sound in enclosed space; persistence of sound Applications Stethoscope, megaphone, ear trumpet use reflection of sound
Doppler Effect
Concept Details Definition Apparent change in frequency of sound when source and observer are in relative motion Source approaches Frequency appears to increase (higher pitch); wavelength decreases Source recedes Frequency appears to decrease (lower pitch); wavelength increases Everyday example Ambulance siren — higher pitch approaching, lower pitch moving away Applications RADAR speed guns, SONAR, measuring star velocities (red shift/blue shift), medical Doppler ultrasound Not applicable when Source and observer both stationary relative to each other Light analogy Red shift (receding — lower frequency); Blue shift (approaching — higher frequency)
SONAR
Fact Details Full form Sound Navigation and Ranging Uses Detecting underwater objects (submarines, depth of ocean, fish shoals) Principle Ultrasonic waves sent; echo received; distance = (speed x time) / 2 Invented Paul Langevin (1917, during World War I)
Quick Recall — PSC Favourites
Question Answer Speed of light in vacuum? 3 x 10^8 m/s Speed of sound in air? 343 m/s (approximately) Sound travels fastest in? Solids Human audible range? 20 Hz to 20,000 Hz Myopia corrected by? Concave lens Hypermetropia corrected by? Convex lens Rear-view mirror type? Convex mirror Shaving mirror type? Concave mirror Rainbow is caused by? Dispersion + total internal reflection + refraction VIBGYOR — most deviated colour? Violet Least deviated colour? Red Doppler effect for approaching source? Higher pitch (increased frequency) SONAR uses which waves? Ultrasonic waves Minimum distance for echo? 17.2 metres Optical fibre works on? Total internal reflection Twinkling of stars due to? Atmospheric refraction Refractive index of diamond? 2.42 Unit of power of lens? Dioptre (D)
