^Polishing lenses When a mirror is polished it becomes a mirror of focal length ‘f’ given by Here f1 & f2 are the focal lengths of surfaces where a ray of light strikes for 1st & 2nd time respectively. As the ray of light strikes the 1st surface twice, hence its contribution is considered twice.
^Displacement method This method is used in the labs to find the focal length of a convex lens. Consider an object placed between a thin convex lens of focal length ‘f’ & a screen at a distance ‘D’ from the screen. Using Lens formula for this problem one can write: To get two distinct images […]
^Cutting a lens (a) If a lens of focal length f is given a longitudinal cut (along aperture) into two equal halves as shown in fig. then the focal length of each half becomes 2f. (b) If the lens is given a transverse cut (at right angles to aperture) into two halves by a plane […]
^Combing two convex lenses 1. Consider a parallel beam of light incident on a combination of two lenses separated by a distance ‘d’ in air or vacuum. Case (a): The final beam after refraction from the two lenses becomes parallel if d = f1 + f2 Case (b): The final beam after refraction from the […]
^Combination of lenses Two or more lenses are combined to Increase magnification. Make final image erect. Reduce certain aberrations. If two thin lenses of focal lengths f1 and f2 are separated by a distance d then the effective focal length and power of the combination is given by: 1. 2. P = P1 + P2 […]
^Image formation by a lens (a) A concave lens always form virtual, erect & diminished image irrespective of the position of the object. (b) With a convex lens following possibilities are there Position of object Ray diagram Image produced At ∞ At F Real (inverted) Extremely Diminished m < < 1 Beyond C i.e. Between […]
^Image formation rules 1. A ray passing through optical center of any lens convex or concave at any angle to principal axis goes undeviated. 2. An oblique passing through focus of any lens convex or concave at any angle to principal axis becomes parallel to principal axis after refraction. 3. A ray parallel to principal […]
^Curved surface refraction formula It is a general expression, applicable to both convex & concave surface, for both point & extended object placed in any medium rare or denser, for any type of image formed (real or virtual). While using this result keep in mind following points: All distance are measured from the pole P […]
^Porro – prisms A Porro – prisms is a totally reflected is a right handed isosceles prisms having ∠C = 420, μ = 1.5 and ∠i = 450. These prisms are used to bend light by 90º or by 180º & to invert images without changing their size. Following are few advantages of TRPs over […]
^δ without θ Under this condition This combination is also called Achromatic prism combination.
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