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Chapter 11 & 12: Online NCERT Summary Class - VI (Science) for UPSC CSE
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This lesson covers the topics related to Light, Shadows and Reflections from chapter 11 and 12 of class 6 Science NCERT. Some important concepts summary which one will be coming across in this lesson are, Luminous objects, visibility, transparent, opaque, translucent, Shadow, pinhole camera, and natural pinhole. Roman has also briefed about Reflection, and Periscope with appropriate illustrations. He shifts his focus next on explaining the concepts dealt in perception with Electricity and Circuits. Here one will learn the basics definitions and brief about Electricity, Electric cell, and Electric bulb. He also speaks about the invention and inventor of the electric bulb and then explains fundamental concepts pertaining to electronic circuits. Here, one will know about conductors, insulator, switch, closed electric circuit and much more. ​

## Roman Saini is teaching live on Unacademy Plus

Roman Saini
Part of a great founding team at Unacademy with Gaurav, Hemesh. Movies, Guitar, Books, Teaching.

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HERE IS ANOTHER AWESOME LESSON FROM THE PUREST OF THE PURE SOUL ON THIS PLANET EARTH.....LONG LIVE ROMAN SIR...AND LONG LIVE UNACADEMY TEAM.... FEELING BLESSED TO BE BORN IN ''ROMAN ERA''....THANK U IS NOT THE WORD...SALUTE TO ALL MOTERS OF FOUNDING FATHERS AND GREAT EDUCATORS AND OTHER CONTRIBUTORS OF UNACADEMY...
Change in light direction when it passes from one medium to another medium is called refraction, not reflection For eg : If you put scale in water, you observe that the scale is bent at the interface of water and air, this is due to refraction Mirrages also form due to refraction only
3 years ago
correct
sir let me bring to ur kind notice that , formation of rainbow is the result of refraction of light. not by total internal reflection . plz correct me if i am wrong. formation of vibgyor is result of refraction of light.
Divyajit DJ
2 years ago
formation of rainbow is due to reflection , refraction and dispersion of light
sir we want mock tests after each class sir
roman but in rainbow dispersion is majorly responsible, though reflection and reflection too contribute and refraction is when there are 2 medium and reflection is the light is reflected by the same angle at which it fall on an object and when the angle of incidence exceed a cetrain limit then only refraction happens. correct me if i am wrong
Pooja Rawat
2 years ago
in the formation of a rainbow total internal reflection occurs at the rear of the rain drop-the water-to-air interface. therefore in order for a rainbow to be visible, the angle of incidence at that interface must be greater than the critical angle. therefore main reason behind the formation of rainbow is total internal reflection.
1. Class 6 Science NCERT Part 6: Chapter 11-12 Presented by Dr. Roman Saini

2. About me MBBS, AIIMS 706-1334 EST Cleared CSE-2013 Loves playing Guitar, Movie Buff * Course Fee : Contribute Follow me on Unacademy https://unacademy.in/user/RomanSaini

3. Chapter 11: Light, shadows and reflections , Luminous objects: objects emitting their own light. Ex: Stars like sun Light will fall on an object first and then it will travel to our eyes, only then it will be visible (unless it is luminescent) On basis of visibility, passage of light, objects are: Transparent (absolutely clearly), opaque (nothing at all) and translucent (not very clearly, somewhat in middle) screen in the background, gives an idea about shape of object, may mislead also Light travels in a straight line

4. Pinhole camera: A light proof box, without a lens, with a single small aperture (pinhole). Light passes through this single point and produces an inverted image on opposite wall of the box. Natural pinhole: Small spaces in between tree leaves * Reflection: Change in direction of light (technically wave front) between 2 different media and its return in media of origin , Mirrors, lakes, ponds etc. are reflecting surfaces Periscope: Instrument which make observation of an object possible, which is otherwise not in direct line of sight of observer's current position.

5. 1 C1 2 C3/b C3/02

6. Chapter 12: Electricity and Circuits Electricity: Physical phenomenon-presence and flow of electric charge. Leads to lightning, static electricity, electromagnetic induction and electrical current. Carelessness: Can cause injury, including death (Our body is a conductor) Electric cell: Metal cap (+) metal disc (), chemicals stores electricity, once started it goes on depleting (even when not in use). Alessandro Volta Joining these 2 ends without a switch or device, leads to consumption of chemicals very fast. s Electric bulb: Thin wire in bulb that gives light - filament (W, Tungsten, break leads to bulb being fused). Bulb also has 2 terminals (base+ metal tip of base, fix so they don't touch each other), Thomas Alva Edison

7. Filament of the bulb is connected to its 2 terminus. Bulb glows when electric current passes through it Material that allow current to pass through them : Conductor (metals like copper, silver, iron) Switches, electrical plugs and sockets Doesn't allow, high resistivity : Insulator (air, plastic, rubber, wood, ceramic, polyethylene, paper, mineral oil), touchable or exposed parts are covered by insulators- electrical wires plug tops, switches switch: simple device used to break/ complete electric circuit Closed electric circuit Electric current passes from one terminal to another, direction of current is form + terminal to terminal Why rubber gloves are used by electrician, screwdrivers, testers also have plastic covering: (rubber is bad conductor)