Explore topic-wise InterviewSolutions in .

This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

1.

What is an equiconvex lens ?

Answer»

If both surfaces of lens have the same radius of curvature, the lens is called equiconvex.
Discussion
2.

An equiconvex lens of focal lenght 15 cm is cut into two halves of thickness. Find the  focal length of each half.

Answer»

From the lensmaker's equation, we have a symmetrical lens with R1 = -R2, and because it is a convex lens, R1>0. Then: 

1/(15 cm)= (n-1)*(1/R1-1/R2) 

1/(15 cm)= (n-1)*(2/R1) 

1/(30cm) = (n-1)/R1 

The new lenses produced by cutting the original lens in half (and we assume the cut is a flat surface) will have focal lengths: 

1/f = (n-1)*(1/R1 + 1/infinity) 
1/f = (n-1)*(1/R1 + 0) 
1/f = (n-1)/R1 

But we already showed that (n-1)/R1 = 1/(30 cm), so the focal length of each half of the lens is 30 cm.
Discussion
3.

Short-shightedness cannot be corrected by convex lens,why?

Answer»

People who are 'short sighted' cannot see things that are far away. They can only see things that are close to them. This is because the eye refracts the light and brings it to a focus before it reaches the retina. This is corrected by using a concave or a diverging lens.
Discussion