linear magnification of a mirror is -v/u and in the lens, it is v/u. why is negative in the mirror and positive in the lens. explain in detail

Asked by modi72879 | 17th Nov, 2017, 07:17: PM

Expert Answer:

Real Images

  • Real Image is an image which can be projected onto a screen.
  • Real images are always located in front of the mirror and behind the lens.
  • Real images are always inverted and never upright.
  • Concave lenses, Convex mirrors and plane mirrors always form virtual images and can never form real images.

Virtual Images

  • Virtual Image is an image which cannot be projected onto a screen.
  • Virtual images are always located in behind the mirror and in front of the lens.
  • Virtual images are always upright and never inverted.
 Linear magnification:
 - Also known as lateral or transverse magnification is the ratio of image length to object length measured in planes that are perpendicular to the optical axis.
 
Magnified image for mirror:
- The image length in the formula of 'm' for mirror is taken as negative because, the image distances i.e 'v' are always negative for virtual images.
- As the magnified image from a mirror is a virtual image, 'v' is taken as negative and that is why the formula of 'm' for mirror becomes, -v/u.
 
Magnified image for lens:
- As the magnified image from the lens is real image, the image distance 'v' is taken positive and the formula of magnification 'm' becomes 'v/u'.
However, in certain cases which involve more than one lens, the object distance can be negative.
 

Answered by Abhijeet Mishra | 20th Nov, 2017, 05:16: PM

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