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What is light?
- It is the part of the electromagnetic spectrum that our eyes can detect.
- Travels in a straight line.
What is Umbra?
- It is a dark shadow with sharp edges
- Formed due to a small source of light (point source)
What is Penumbra?
- A partial shadow which varies in brightness
- from very dark near the umbra - to very dark near the outer part of the shadow, where more light can reach.
- Formed due to a large source of light (extended source)
What are the two laws of reflection?
- 1)The incident ray, reflected ray and the normal all lie on the same plane.
- 2)The angle of incidence is equal to the angle of reflection.
(There are 2 types of reflection : Regular reflection and Diffused reflection)
Incident Ray and Emergent Ray are parallel to each other!!
What is meant by a 'plane mirror'?
The surface of a plane mirror is straight and smooth.
Properties of Images formed by Plane Mirrors.
- Same size
- Same distance
- Laterally inverted
What is Refraction?
It is the bending effect of light rays as they travel from an optically less dense medium to an optically denser medium and vice versa.
Optical medium : a transparent material, one that light can pass through (water, air, glass)
What are the causes of Refreaction?
Refraction occurs because light travels at different speeds in different media
- -Light is refracted TOWARDS the normal when it passes from a LESS dense medium to a MORE dense medium.
- -Light is refracted AWAY from the normal when it passes from a MORE dense medium to a LESS dense medium.
formula to remember : MuLA dari LuMuT
Laws of Refraction
1) The incident ray, the refracted ray and the normal all lie on the same plane
2) The ratio of the sine of the angle of incidence and the sine of angle of refraction is always constant (n, refractive index) for a particular medium. (SNELL'S LAW)
- If the light ray is travelling from a LESS DENSE medium to a MORE DENSE medium,
- But if the light ray is travelling from a MORE dense medium to a LESS dense medium,
- No units
- The speed of light in a vacuum/air, c is
- The formula for finding refractive index, when speed of light is given is
- where medium 1 is the less dense medium and medium 2 is the denser medium.
Another formula for finding Refractive Index (n)
- , and
Dispersion of white light
- -White light is made up of 7 colours (ROYGBIV)
- -Splitting white light into these 7 colours is known as dispersion of white light.
- CAUSES OF DISPERSION
- -Different colours travel at different speeds in glass, where red deviates the least and violet deviates the most. (In a vacuum/air, all colours travel at the same speed, 3.0 x 108
-Each colour of light gets refracted by a different angle as it passes between the air & the glass.
- When light passes from a denser medium to a less dense medium, the emergent ray is refracted away from the normal.
- As the incident angle increases, eventually the refracted angle will be 90o.
- When this happens, the incident angle is known as CRITICAL ANGLE.
- Definition : The angle of incidence in the optically denser medium for which making the angle of refraction equals 90o in the less dense medium.
Total Internal Reflection
- When the angle of incidence is increased beyond the critical angle, the light is reflected from the boundary.
- This is known as TOTAL INTERNAL REFLECTION.