Edexcel GCSE Physics

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Harriet Carpenter
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1 Edexcel GCSE Physics Tpic 5: Light and the Electrmagnetic Spectrum Ntes (Cntent in bld is fr Higher Tier nly)

$Angle is the angle f the entering ray - Reflected Angle is the angle f the exiting ray Reflectin (Physics nly) - Incident angle = reflectin angle - Angles are always measured frm nrmal Refractin$

2 Ray Diagrams (Physics nly) - Arrws shw directin f light travelling - The nrmal is an (imaginary) dashed line which is perpendicular t the surface, and frm which all angles are measured frm - Incident Angle is the angle f the entering ray - Reflected Angle is the angle f the exiting ray Reflectin (Physics nly) - Incident angle = reflectin angle - Angles are always measured frm nrmal Refractin (Physics nly) - If entering a denser material, it bends twards the nrmal - If entering a less dense material, it bends away frm nrmal Ttal Internal Reflectin (TIR) (Physics nly) - This ccurs when the light is passing frm a denser medium int a less dense medium (glass t air) - If the angle f incidence is equal t the critical angle, the refracted ray will pass alng the bundary and nt exit the medium The critical angle is a unique angle fr each tw media (the critical angle fr glass-air is different t glass-water) - Fr larger angles, the light internally reflects (fllwing the abve law f reflectin) back int the glass Denser medium Critical Angle Summary fr glass t air (Physics nly) - If angle LESS than critical angle, light refracts away frm nrmal - If angle EQUAL t critical angle, light passes alng bundary - If angle MORE than critical angle, light reflects Specular Reflectin (Physics nly) - Mirrr reflectin, fllwing law f reflectin, fr a smth surface (all light incident at the same angle all exit at the same angle) Diffuse Reflectin (Physics nly) - Light hitting a rugh surface incident ray is reflected at many angles rather than just ne angle Clur (Physics nly) - Each clur is just a certain wavelength in visible light - All the clurs tgether make up white light Opaque Material (Physics nly) - Objects appear t have a certain clur (e.g. green ), as ut f the incident white light nly that certain clur light (green light) is reflected, all ther clurs are absrbed

Clur Filters (Physics nly) - All ther clurs are absrbed, and nly a certain clur is allwed t pass thrugh - s nly a certain wavelength is transmitted thrugh the filter Lenses (Physics nly) - Fcal

3 Clur Filters (Physics nly) - All ther clurs are absrbed, and nly a certain clur is allwed t pass thrugh - s nly a certain wavelength is transmitted thrugh the filter Lenses (Physics nly) - Fcal Length is the distance between the lens and the fcal pint - Fcal Pint is the pint where all hrizntal rays meet after passing thrugh the lens - Pwer f the lens is the inverse f the fcal length Shrter fcal length, greater pwer Thicker lens means shrter fcal length, s greater pwer Cncave Lenses (Physics nly) - Caves inward - Thinner at centre than at edges - Spreads light utwards - Light appears t have cme frm the fcal pint Draw hrizntal ray frm tp f bject t lens Draw a faint line frm fcal pint t pint where the ray hits the lens The ray exits the lens alng the same directin as the faint line (shwn by blue line) - It is used t spread ut light further images.slideplayer.cm E.g. they are used t crrect shrt-sightedness As light is fcused in frnt f the retina, s needs t be spread ut slightly t be able t be fcused nt retina Cnvex Lenses (Physics nly) - Fatter at centre - Fcuses light inwards - Hrizntal rays fcus nt fcal pint - They are used fr magnifying glasses, binculars and t crrect lngsightedness, as it fcuses the rays clser penstudy.cm Images (Physics nly) - A Real image is an image prduced at the ppsite side f the lens t the bject The abve image fr a cnvex lens is a real image - Virtual images appear t cme frm the same side f the lens t the bject This is if the bject lies clser t the lens than the fcal pint (F) leydenscience.rg

EM Waves - All electrmagnetic waves transfer energy frm surce t bserver The waves cntain energy, fr example micrwaves which transfers energy frm surce t fd - They are transverse waves - They all

4 EM Waves - All electrmagnetic waves transfer energy frm surce t bserver The waves cntain energy, fr example micrwaves which transfers energy frm surce t fd - They are transverse waves - They all travel at the same speed in a vacuum westernreservepublicmedia.rg Need t learn the main grups, and in which rder (fr increasing wavelength r frequency) - EM waves d nt need particles t mve - In space, all waves have the same velcity (speed f light) - They can transfer energy frm a surce t absrber Micrwave surce t fd Sun emits energy t Earth - Our eyes can nly detect visible light - Materials interact with EM waves differently depending n the wavelength Glass can transmit visible light, reflect/absrb UV and IR Relatinships - As speed is cnstant fr all EM waves in a vacuum - As wavelength decreases, frequency must increase - As frequency increases, energy f the wave increases All Bdies emit radiatin - The higher the temperature, the mre intense (and mre wavelengths) will be emitted

5 Temperature - It must radiate the same average pwer that it absrbs t remain at a cnstant temperature - If It absrbs mre pwer than it emits the temperature will increase - If it absrbs less pwer than it emits the temperature will decrease - Temperature f the earth this is maintained by the amunt f energy received and emitted frm the sun Shrt-wavelength Infra-red radiatin frm the sun reaches the Earth Sme is reflected by the atmsphere, mst reaches the surface The energy is absrbed and re-emitted as lnger-length IR radiatin This is mstly absrbed by the atmsphere (greenhuse gases, CO 2 etc.) and keeps the Earth warm Danger f the EM spectrum - Higher frequency EM waves have mre energy, s expsure can transfer t much energy t cells, causing them t mutate and ptentially damage them/causing cancer - Micrwaves - Internal heating f bdy cells - Infra-Red - Skin burns - UV - Damage t surface cells and eyes, leading t skin cancer - X-ray/Gamma - Mutatin r damage t cells in the bdy Uses f the EM spectrum, - Radi - Cmmunicatins, satellite transmissin. They can be prduced by scillatins in electrical circuits, r they can induce scillatins in electrical circuits - Micrwave - Cking, cmmunicatin - IR - Cking, thermal imaging, shrt range cmmunicatin, ptical fibres - Visible - Visin, phtgraphy, illuminatin - UV - Security marking, flurescent lamps, disinfecting water - X-ray - Observing internal structure f bjects, airprt/medical scanners - Gamma - Sterilising fd/medical equipment, treating cancer Change in Atms and Nuclei: - Generate radiatins ver a wide frequency range - Be caused by absrptin f a range f radiatin

Light : Reflection And Refraction (Part I Reflection)

$Light : Reflection And Refraction (Part I Reflection)$ 1 Light : Reflectin And Refractin (Part I Reflectin) Light is a frm f energy which enables us t see bjects either frm which it cmes r frm which it is reflected. Luminus bjects are thse bjects which emit