Q.))a point source of light is from a screen and is kept at d focus of a concave mirror which reflects light on d screen. the focal length of d mirror is 20 cm. The ratio of average intensities of the illumination on d screen when d mirror is present and when d mirror is removed is....

(a)36:1

(b)37:1

(c)49:1

(d)10:1

do reply asap plzzzz........

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