One day, after pulling down your window shade, you notice that sunlight is passing through a pinhole in the shade and making a small patch of light on the far wall. Having recently studied optics in your physics class, you're not too surprised to see that the patch of light seems to be a circular diffraction pattern. It appears that the central maximum is about 1 cm across, and you estimate that the distance from the window shade to the wall is about 4 m. Estimate:
a. The average wavelength of the sunlight (in nm)
b. The diameter of the pinhole (in mm).

Given that,

Central maximum = 1 cm

Distance from the window shade to the wall =4 m

We know that,

The visible range of the sun light is 400 nm to 700 nm.

(a). We need to calculate the average wavelength

Using formula of average wavelength

Put the value into the formula

(b). We need to calculate the diameter of the pinhole

Using formula for diameter

Put the value into the formula

Hence, (a). The average wavelength 550 nm.

(b). The diameter of the pinhole is 0.537 mm.

in this image, you can see solar radiation going through ocean water.

no image, but probably absorption

the answer for apex is the lowest