QUANTUM PHYSICS FUNDAMENTALS - Chapter 1, Exercise 1 Solution
==========================================================
Photon Energy from Frequency (E = hf)

PROBLEM
-------
Calculate the energy of a single photon of red light, with a
frequency of 4.3 x 10^14 Hz, using E = hf.

SOLUTION
--------
Using Planck's real relation:

    E = h f

Substitute the given values:

    h = 6.626 x 10^-34 J.s
    f = 4.3 x 10^14 Hz

    E = (6.626 x 10^-34) x (4.3 x 10^14)
    E = 2.85 x 10^-19 J (approximately)

ANSWER: The photon's energy is approximately 2.85 x 10^-19 J.

----
WHY THIS WORKS AS AN ANSWER

E = hf is a direct proportionality - energy scales linearly with
frequency, with Planck's constant as the fixed conversion factor
between the two. Comparing this result to the chapter's own worked
example (green light at 5 x 10^14 Hz, giving about 3.31 x 10^-19 J)
confirms the expected pattern: red light has a lower frequency than
green light, and correspondingly carries less energy per photon -
exactly the real, ordered relationship between color and photon
energy across the visible spectrum.