What visible wavelengths of light are strongly reflected from a 390-nm-thick soap bubble?

So visible wavelength which is possible here is

416 nm and 693.3 nm

Explanation:

As we know that for normal incidence of light the path difference of the reflected ray is given as

so here we can say that for maximum intensity condition we will have

so we have

now for visible wavelength we have

for N = 1

for N = 2

for N = 3

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.