LIGHT
1. Define light.
- Light is defined as a form of energy which gives us the sensation of warmth.
2. Define lens with it's types.
- A transparent refractive medium bounded by two curved surfaces is called lens. It's types are:
a. Concave lens (Diverging lens)- A lens which is thinner at the middle and thicker at the edge is called concave lens.
b. Convex lens (Converging lens)- A lens which is thicker at the middle and thinner at the edge is called convex lens.
3. Define center of curvature.
- The center of the sphere of which the lens is formed is called center of curvature.
4. Define principal axis and optical center.
- The imaginary line joining the two centre of curvature of a lens is called principal axis.
- The mid-point of two centre of curvature is called optical centre.
5. Define principal focus and focal length.
- The point through which the parallel rays of light passes or appears to pass after refrating through the lens is called principal focus.
- The distance between optical center and focus is called focal length.
6. Define focusing.
- The process of adjusting the distance between the lens and screen in order to produce a clear and distinct image is called focusing.
7. Define power of lens with its unit.
- The converging or diverging capacity of a lens is called the power of a lens. Its S.I unit is dioptre(D). And mathematically,
power= 1/focal length
8. Define Magnification.
- The ratio of the length or height of the image to the length or height of the object is called magnification. It does not have any unit. Mathematically,
Magnification(M)= Length of image(I)/Length of object(O)
= Distance of image (V)/Distance of object(U)
9. Define optical instrument and Hand lens.
- Instruments which produce an image of an object by using a lens are called optical instruments.
- A hand lens is a simple microscope with a convex lens and handle.
10. Define camera.
- It is an optical instrument having a convex lens which is used to take photographs of the objects.
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