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NEWTON’S FORMULA

If the distance of object and image are not measured from optical centre (C), but from first and second principal foci respectively, then newton’s formula states Where, distance of object from first focus F1. distance of image from second focus. If medium on either side of lens is same, then . So, Newton’s formula takes […]

POWER OF A LENS

“Power of lens is a measure of the convergence or divergence, which a lens introduces in the light falling on it.” It is defined as the tangent of the angle by which it converges or diverges a beam of light falling at unit distant from the optical centre. Thus, Power of a lens is the […]

TOTAL INTERNAL REFLECTION

When a ray of light travels from an optically denser medium to a rarer medium, the refracted ray is bent away from the normal e.g the incident ray ‘AO1’ is partially reflected (O1C) and partially refracted (O1B), the angle of refraction being larger than the angle of incidence. As the angle of incidence increases, the […]

SIGN CONVENTION OF A LENS

We follow new Cartesian sign conventions. (a) The distance always measured from optical centre. (b) The distance measured to the right of the optic centre is taken as positive and to the left is negative. (c) The height measured vertically upward is positive whereas vertically downward is negative.    

THE EYE

The eye has a nearly spherical shape of diameter 1 inch. The front portion is more sharply curved and is covered by a transparent protective membrane called the cornea. It is this portion which is visible from outside. Behind the cornea, space is filled with a liquid called the aqueous humor and behind that a […]

EFFECTS OF TOTAL INTERNAL REFLECTION

(a) Mirage: It is an optical illusion which occurs due to the phenomenon of total internal reflection. When we are travelling on a road on a hot summer day, the road at a distance appears to be covered with water but when we approach the region, we find that there is no water. This phenomenon […]

DISPLACEMENT METHOD TO DETERMINE THE FOCAL LENGTH OF A CONVEX LENS

If the distance D of an object between an object and screen is greater than 4 times the focal length of a convex lens, then there are two positions of the lens between the object and the screen at which a sharp image of the object is formed on the screen. This method is called […]

DEFECTS OF VISION AND CORRECTION OF EYE DEFECTS USING LENS

The ciliary muscles control the curvature of the lens in the eye and hence can alter the effective focal length of the system. When the muscles are fully relaxed, the focal length is maximum. When the muscles are strained, the curvature of the lens increases and focal length decreases. For a clear vision, the image […]

SPHERICAL ABERRATION

It seems that the reflected ray don’t converge at a point but are distributed in a region. For a concave mirror only those parallel rays which are incident on the mirror near the vertex are focussed at ‘F’, other reflected rays form a fuzzy image. Thus ‘the failure of rays to converge or diverge from […]

LINEAR MAGNIFICATION OF A LENS

It is the ratio of the image height to object height. According to new Cartesian sign convention

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