The principal focal lengths of two lenses in a system of two thin lenses are equal when
Medial on either side of the two lenses are dissimilar
Media on either side of the two lenses are similar
Focal lengths are always equal
None of these
When a single lens produces a coloured image of an object illuminated by white light is known as
Achromatism
Chromatic aberration
Spherical aberration
All the above
Elimination of the chromatic aberration defect in a system of lenses is know as
Achromatism
Astigmatism
Both (a) & (b)
None of these
The aberration produced by the variation of refractive index with wavelength of light are called
Aberrations
Chromatic aberrations
Monochromatic aberrations
None of the above
The modified form of fermat’s principle of least time is
Newton’s principle of stationary time
Fermat’s principle of stationary time
Both (a) & (b)
None of these
Does laws of reflection are derivable from fermat’s principles?
Yes
No
Not satisfactorily
Both (a) & (c)
A concave spherical surface of radius of curvature 100 cm separates two media of refractive indices 1.50 and 4/3. An object is kept in the first medium at a distance of 30 cm from the surface. The position of the image is
28.58 cm
-28.58 cm
-27.58 cm
27.58 cm
The quantity represents
Power of refracting surface
Power of ordinary mirror
Both (a) & (b)
None of the these
Where n1, n2 are refractive indices of the medium and R is the radius of curvature
The focal length of a double convex lens, for which the radius of curvature of each surface is 30 cm and refractive index of glass is 1.50 is
F = 50 cm
F = 40 cm
F = 30 cm
F = 20 cm
The equation is satisfied by
Chromatic doublet
Achromatic doublet
Spherical doublet
Both (a) and (c)