1. Light

2. Light is a electromagnetic radiation - a form of energy. Light travels in a straight line. The direction in which light is travelling is known as a ray. A group of rays is known as a beam. The speed of light is fastest

3. Shadow A shadow is produced when a beam of light falls on an opaque object and it blocks the way of light The part without light is called shadow Nearer the light source, bigger the shadow. Farther the light source, smaller the shadow. Bigger the light source, bigger the shadow and smaller the light source, smaller the shadow. When light source is very near, we can distinguish two dark-light regions of the object.

4. Two types of objects Luminous objects: objects that emit light. they emit light because their atoms get ‘excited’ and they give out energy in the form of light. Most light sources emit light haphazardly however in laser only a narrow, bright beam of light is emitted. Non-luminous objects: objects that don't emit their own light and reflect light of other things. Objects are only visible because of reflection of light. A red object reflects just the red light ray and reflects all other from the spectrum and a black object does not reflect any light ray. –Opaque objects: Light cannot pass through them –Transparent objects: light can pass through them –Translucent objects: light can partially pass through them

5. REFLECTION

6. When an object or wave hits a surface through which it cannot pass through and bounces back. Incident ray: the light ray which strikes a reflecting surface Reflected ray: A light ray that is reflected from the reflecting surface Normal: A line perpendicular to the reflecting surface where the incident ray strikes Angle of incidence: the angle between incident ray and the normal Angle of reflection: Angle between the normal and the reflected ray Plane Mirror: Mirror with flat, smooth surface Virtual Image: Appearance of an object in a smooth, shiny surface that is made by reflection in a mirror Real Image: the image in real world that is reflected to gain the virtual image

8. Law of reflection Angle of reflection is always same as angle of incident Incident ray and reflected ray are on opposite sides of the normal The incident ray, normal and the reflected ray lie on the same plane

9. Properties of mirror image Virtual Laterally inverted as far behind the mirror as the object is in front; line joining image and object is always perpendicular to mirror same size as the object

10. Finding Position of the image

12. REFRACTION: BENDING OF LIGHT

14. Refraction is the bending of light at the interface of dissimilar substances when it moves from one medium to another. Light ray bends towards the normal while moving from less denser to more denser medium such as from air to glass. Light ray bends away from the normal while moving from denser to less denser medium such as from glass to water. Refraction occurs due to change in speed of light as it travels through different mediums.

15. Refraction through parallel sided block Emerging and incident rays are parallel

16. Refraction through prism

17. Dispersion The phenomenon by which a ray of white light splits into its constituent colors when it is passed through a transparent medium is known as dispersion. The band of seven colors is known as spectrum. This is due to refraction of light as all colors travel at different speeds.

19. Refractive Index For example, if a ray is travelling at the speed of 300000 km/s in air and enters a glass block changing its speed to 200000 km/s, then we can calculate the refractive index of that glass block by dividing the previous speed with the new speed e.g. 300000/200000 therefore the refractive index of glass block is 3/2.

20. Light through the eye

21. The light passes through the transparent cornea and refraction happens. Light again refracts through the aqueous humor. The iris adjusts its size to control the area of pupil exposed to light From the pupil, light refracts through the lens Lens has cilliary muscles which helps it adjusts its size according to the distance of the object The lens then passes light ahead which again refracts from vitreous humor which adjusts the size of image and at last displays an inverted image on the retina The photosensitive cells on the retina - rods (help to see in night) and cones (help to see in day) which are made up of Rhodopsin (has Vitamin A) which send electric impulses of the image through optical nerve Lack of Vitamin A can cause night blindness

22. Total internal reflection When light passes from a denser medium to a less denser medium, the light ray is refracted away from the normal. As the angle of incidence increases, a time comes when the refracted ray is 90 degree to the normal. This angle of incidence is known as the critical angle. After the critical angle, no refracted ray is visible, and a reflected ray is visible.

24. LENSES

25. Lenses are used in optical instruments such as cameras, spectacles, microscope and telescope. They often have curved surfaces Lenses Converging (Convex) Diverging (Concave)

26. Converging lens C – Optical centre – The centre of the lens Principal axis – The line through C at right angles to the lense F – Principal focus FL – Focal length (Distance between C and F)

27. Diverging lens C – Optical centre – The centre of the lens Principal axis – The line through C at right angles to the lens F – Principal focus FL – Focal length (Distance between C and F)

28. Convex Lens Ray Diagram