NCERT Physics Class 12 Exemplar Ch 9 Ray Optics and Optical Instruments Part 1
Doorsteptutor material for NSO is prepared by world's top subject experts: fully solved questions with step-by-step explanation- practice your way to success.
Very Short Answer
Q 17. Will the focal length of a lens for red light be more, same or less than that for blue light?
Ans:
As the refractive index for red is less than that for blue, parallel beams of light incident on a lens will be bent more towards the axis for blue light compared to red.
Thus the focal length for blue light will be smaller than that for red.
Q 18. The near vision of an average person is 25cm. To view an object with an angular magnification of 10, what should be the power of the microscope?
Ans:
The near vision of an average person is 25cm. To view an object with magnification 10,
Q 19.An unsymmetrical double convex thin lens forms the image of a point object on its axis. Will the position of the image change if the lens is reversed?
Ans:
No. The reversibility of the lens makes equation.
Q 20 Three immiscible liquids of densities and refractive indices are put in a beaker. The height of each liquid column is . A dot is made at the bottom of the beaker. For near normal vision, find the apparent depth of the dot.
Ans:
Let the apparent depth be for the object seen from then
If seen from the apparent depth is.
Seen from outside, the apparent height is
Q 21. For a glass prism the angle of minimum deviation is equal to the angle of the prism. Find the angle of the prism.
Ans:
At minimum deviation
Given
Minimum Deviation Equal to the Angle of the Prism