Question

A concave refracting surface of a medium having refractive index $\mu$ produces a real image of an object (located outside the medium) irrespective of its location

• A. always
  
• B. may be if refractive index of surrounding medium is greater than 1.
• C. may be if refractive index of surrounding medium is less than $\mu$
• D. none of the above

Answer 1

The correct option is D none of the above

We have $\frac{\mu }{v}-\frac{{\mu }_1}{-u}=\frac{\mu -{\mu }_1}{-R}$

Surface concave to denser medium, i.e. rays go from denser to rarer medium.


Alternative solution:

$\frac{\mu }{v}-\frac{{\mu }_1}{u}=\frac{\mu -{\mu }_1}{R}$
Here, using sign convention,

$u=-ve,R=-ve,v=+ve$

$\frac{\mu }{v}=\frac{\mu -{\mu }_1}{-R}-\frac{{\mu }_1}{u}=+veif\mu <{\mu }_1$
Hence, the correct answer is option (d).

Why this question? Note: For the image to be real, refracted rays should actually meet. So, v is positive in this case.