Question

Find the focal length of lens.​

Answer 1

Answer:

Explanation:

Refractive index of the lens = 1.5 =Refractive index of medium 

the lens in a medium (liquid) will be act like a plane of glass.

 Its focal length will be infinte 

By using the formula of lens maker.

1/f = (u - 1) (1/R1 - 1/R2)

1/f = (u2/u1 -1) (1/R1 - 1/R2)

    u1 = u2

1/f = 0

thus, f = infinity 

Answer 2

given

converging lens is imarge in grass whose refractive index is less than glass refractive index so it beehive like mirror whose focal length is infinity

since

1/f = (u - 1)(1/R1 - 1/R2)

since

u2/u1 = u

u = speed of light in raerer medium/speed of light in denser medium

there for u1 = u2

so

1/f = (u2/u1 - 1)(1/R1 - 1/R2)

1/f = 0

so

f = infinity