Auniform thin film of n=1.33 is on top of glass (n=1.5). When monochromatic light with tunable wavelength is directed from above, the reflected light is minimum when λ=505nm, and maximum when λ=650nm. What is the minimum thickness of the film?

Explanation:

There is reflection ( two times ) from upper and lower surface of the film . In both cases , reflection is from low to  high density medium so there is change in phase of 180 twice .

So for constructive interference

2μd = n λ₁ , d is thickness required , λ is wavelength n₁ is order of  bright fringe

For destructive interference ( minimum light )

2μd = (2n+1) λ₂/2

n λ₁ =(2n+1) λ₂/2

(2n+1) / 2n = λ₁ / λ₂

= 650 / 505

=   5 / 4 ( approx )

2n = 4

n = 2

2μd = n λ₁

2 x 1.33 x d = 2 x 650 nm

d = 488.72 nm

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.

answer: 31, 5556. 952 seconds