Question:

A square of side 3 cm is located at a distance 25 cm from a concave mirror of focal length 10 cm. The centre of square is at the axis of the mirror and the plane is normal to axis of mirror. The area enclosed by the image of the square is

Updated On: Jul 6, 2022
  • $4\, cm^2$
  • $6\, cm^2$
  • $16\, cm^2$
  • $36\, cm^2$
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The Correct Option is A

Solution and Explanation

Linear magnification, $ m = \frac{I}{O}=\frac{f}{u-f}$ $ = \frac{10}{25-10} $ $m = \frac{10}{15}=\frac{2}{3}$ Areal magnification $=m^2 = \frac{4}{9} $ $$ Area of image $ = \frac{4}{9} \times$ area of object $ = \frac{4}{9} \times (3)^2 = 4\, cm^2$
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Notes on Ray optics and optical instruments

Concepts Used:

Ray Optics and Optical Instruments

Optics, deals with the determination of behaviour and the properties of light, along with its interactions with the matter and also with the instruments that are used to detect it.

Ray optics is also known as the geometrical optics and it is a branch of science which describes light propagation.

Reflection is the change in direction of light at an interface in-between two different media so that the wave-front returns into a medium from which it was originated.

Speed of light is the rate at which the light travels in free space.

A phenomenal change in image formed when the light is passed from one medium to another which is called Refraction.

Total Internal Reflection is the reflection of light when the light ray enters into a rarer medium from a denser medium and the angle of incidence is higher than the critical angle of incidence then that light ray will be reflected back to the denser medium.

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