Question

Focal length of a lens is determined by
a) Object distance
b) Image distance
c) Radii of curvature of its surfaces and nature of material of the lens
d) None of the above

Answer 1

Explanation:

when the lens is focused at infinity

Answer 2

Answer:

Focal length depends on colour of light because changing color changes wavelength which in turn changes the convergence point, so focus position changes and hence focal length also changes. It also depends on curvature of lens,

i.e.

f

1

=(

M

1

M

2

−1)(

R

1

1

−

R

2

1

)

where R

1

,R

2

are radius of curvature of two sides of lens. And M

2

is refractive index of material of which lens is made of and M

1

is refractive index of surrounding medium. And by this formula we see that focal length is also dependent on the material of lens.

Explanation:

ALL OF THE ABOVE