what is focal length ? define brifly ?
Answers
Answer:
The line joining the centres of curvature of both the surfac es of a line is called the principal axis of the lens. The point situated on the principal axis such that the rays moving from it or coming towards it become parallel to the principal axis after refraction through the lens, is called the first focus of the lens. The distance from optical centre to first focus is called the first focal length. Similarly the point on the principal axis, where the rays coming parallel to the principal axis actually meet or appear to meet after refraction through the lens is called the second focus of the lens. The distance from the optical centre to the second focus is called the second focal length; when we write focus we mean the second focus and when we write focal length we mean the second focal length; when the same medium occurs on both sides of the lens, the first focal length and the second focal length become equal to each other
FOCUS
>> The point where all the light rays converges is called as Focus
>> It Is also called as Image point
>> It is denoted by F
Pole
>> Centre of the mirror is also called as Pole
>> It is denoted by P
FOCAL LENGTH
>> The distance between Focus and Pole is called as focal length
>> It is denoted by " f "
Hope it helps