Question

what is principal focus of alum

Answer 1

When rays of light are incident on a lens or a mirror, they refract/reflect to a certain point on the principal axis. This point is called the focus of the lens/mirror.

This point can be anywhere on the principal axis, depending on how the rays are initially travelling.

 

Principal focus is a special case of focus wherein the rays are travelling parallel to the lens/mirror and then refract/reflect to a particular point on the axis.

Generally the rays are parallel if the object is at infinity.

Answer 2

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$\Large\fbox{\color{purple}{CORRECT \: QUESTION}}$

DEFINE THE FOLLOWING TERMS IN RELATION TO SPHERICAL MIRRORS

PRINCIPAL FOCUS

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$\Large\fbox{\color{purple}{ SOLUTION }}$

★ PRINCIPAL FOCUS ★

IT IS A POINT ON PRINCIPAL AXIS WHERE ALL REFLECTED RAYS ARE EITHER CONVERGE OR DIVERGE

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