THE PRACTICE STUDIO
Go slowly. Ask why. Make it yours.
PRACTICE / Photon energy and momentum
Energy of a red photon
Light has vacuum wavelength 620 nm. Use hc = 1240 eV·nm and 1 eV = 1.6 × 10⁻¹⁹ J.
Find the energy of one photon in eV.
Organize the givens & assumptions
- λ = 620 nm
- hc = 1240 eV·nm
Vacuum wavelength; monochromatic photons; use the supplied hc and electronvolt conversion.
Study with a tutor prompt
Copy this into your AI assistant, then describe where you got stuck. It asks the tutor to coach you one step at a time. Check its reasoning against the lesson.
Opening this prompt marks this practice attempt as assisted.
Problem: Energy of a red photon
Light has vacuum wavelength 620 nm. Use hc = 1240 eV·nm and 1 eV = 1.6 × 10⁻¹⁹ J.
Question: Find the energy of one photon in eV.
Givens:
- λ = 620 nm
- hc = 1240 eV·nm
Assumptions: Vacuum wavelength; monochromatic photons; use the supplied hc and electronvolt conversion.
Choices (LaTeX):
A. 1240\ \mathrm{eV}
B. 4\ \mathrm{eV}
C. 2\ \mathrm{eV}
D. 0.5\ \mathrm{eV}
Ask for my approach first. Help me distinguish a physical misconception from an algebra error without revealing which choice is correct.
Tutoring approach:
Act as a patient physics tutor. Ask what I understand and what I have tried, then wait for my reply. Teach one step at a time; do not give the final answer or a complete solution immediately. Start with a physical picture. Define unfamiliar symbols and operators, explain signs and units, and state the model's assumptions. Give progressively stronger hints only when I need them. Ask me to predict a change before calculating it. When I finish, help me check dimensions and a limiting case, then ask one related transfer question. If information is missing or ambiguous, ask rather than inventing it. Distinguish exact results from approximations and acknowledge uncertainty.Start with the smallest hint.
Work through it with me.
One decision at a time. Pause, predict, then unpack the algebra.
Use the supplied eV·nm constant with wavelength in nanometres so those length units cancel.
Choose a physical relation
A photon's energy is set by its frequency, which equals c divided by the vacuum wavelength.
Isolate what is asked
Use the supplied eV·nm constant with wavelength in nanometres so those length units cancel.
Why is this step valid?
Using hc in eV·nm requires wavelength in nm and directly yields electronvolts.
Substitute and interpret
A 620 nm photon has energy 2 eV, or 3.2 × 10⁻¹⁹ J; longer wavelengths mean less energy per photon.
Visible photons carry energies of a few electronvolts. This red-light photon is lower in energy than a 310 nm photon, which would carry 4 eV with the stated constant.
TRY THE IDEA AGAIN
Double the beam intensity without changing colour. Does each photon gain energy?
YOUR LEARNING NOTE
How does this idea feel now?
Confidence is a reflection, not proof of mastery.
Loading… · 0 answer checks
Loading your learning note…