The lens-makers’ equation applies to a lens immersed in a liquid if n in the equation is replaced by n2/n1. Here n2 refers to the index of refraction of the lens material and n1 is that of the medium surrounding the lens. (a) A certain lens has focal length 79.0 cm in air and index of refraction 1.55. Find its focal length in water. (b) A certain mirror has focal length 79.0 cm in air. Find its focal length in water.

a

The focal length of the lens in water is  

b

The focal length of the mirror in water is  

Explanation:

From the question we are told that

    The index of refraction of the lens material =

    The index of refraction of the medium surrounding the lens =

The lens maker's formula is mathematically represented as

Where is the focal length

            is the index of refraction

            are the radius of curvature of sphere 1 and 2 of the lens

From the question When the lens in air  we have  

    When immersed in liquid the formula becomes

The ratio of the focal length of the the two medium is mathematically evaluated as

From the question

      = 79.0 cm

and the refractive index of water(material surrounding the lens) has a constant value of  

b

The focal length of a mirror is dependent on the concept of reflection which is not affected by medium around it.

the body's situation won't change the forces are equal opposit and on the same body

force is mass*acceleration.

we have a very small mass: 11.4*0.001 kg

if we want 0.035n of force, we need an acceleration:

0.035 = 11.4*0.001*a

a = 0.035/(11.4*0.001) m/s^2