Question

Light of which of the following colours will have the maximum energy in a photon associated with it?

• A. Red light
• B. Yellow light
• C. Green light
• D. Blue light

Hint:

In visible light: Red → lowest energy, Violet → highest energy. If violet is absent, choose the shortest wavelength colour available.

Answer 1

The Correct Option is D

Concept: Energy of a photon is given by Planck’s equation: \[ E = h\nu = \frac{hc}{\lambda} \] Where:

\( h \) = Planck’s constant
\( \nu \) = frequency
\( \lambda \) = wavelength
Thus:

Higher frequency \( \Rightarrow \) higher energy
Shorter wavelength \( \Rightarrow \) higher energy

Step 1: Compare visible light colours. In the visible spectrum:

Red → longest wavelength, lowest frequency
Yellow → shorter than red
Green → shorter than yellow
Blue → shortest wavelength among given options

Step 2: Determine maximum energy. Since energy is inversely proportional to wavelength: \[ E \propto \frac{1}{\lambda} \] The colour with the shortest wavelength has the maximum photon energy.
Step 3: Conclusion. Blue light has the highest frequency and hence maximum photon energy.

Answer 2

A photon's energy is tied to its frequency (or equivalently, inversely tied to its wavelength) through \( E = h\nu = \dfrac{hc}{\lambda} \). Since visible colours differ mainly in wavelength, comparing the typical wavelength of each option tells us which photon carries the most energy.

1. Red light: Red sits at the long-wavelength end of the visible spectrum (roughly 620-750 nm). Since energy is inversely proportional to wavelength, this long wavelength corresponds to the lowest photon energy among the four options.
2. Yellow light: Yellow's wavelength (roughly 570-590 nm) is noticeably shorter than red's, so its photons carry somewhat more energy than red photons, but yellow is still on the longer-wavelength half of the visible range.
3. Green light: Green's wavelength (roughly 495-570 nm) is shorter still, giving it higher photon energy than both red and yellow, but it remains longer than blue's wavelength.
4. Blue light: Blue has the shortest wavelength of the four (roughly 450-495 nm). Since \( E \propto \frac{1}{\lambda} \), this shortest wavelength directly translates into the highest photon energy of the group.

Ranking the four by wavelength from longest to shortest gives red, yellow, green, blue, which means ranking them by photon energy from lowest to highest gives the exact same order, with blue coming out on top.

Therefore, the correct answer is Blue light.