Light & Technology
How radiation affects matter, and how we send information
Do Now: You can sit in front of a bright lamp for hours without getting sunburned, but 20 minutes of summer sun can burn you. What’s the difference?
Sunlight contains ultraviolet light. Each UV photon carries enough energy to damage molecules in your skin. Lamp light is brighter in your room, but each of its photons carries less energy.
Try It First
Slide from radio waves to gamma rays and watch the energy of one photon change.
Lessons
NYS P-12 Science Learning Standards, Physics: HS-PS4-4 — Evaluate the validity and reliability of claims in published materials of the effects that different frequencies of electromagnetic radiation have when absorbed by matter. HS-PS4-2 — Evaluate questions about the advantages of using digital transmission and storage of information.
How a Solar Panel Works
A solar panel converts sunlight into electrical energy. When a photon with enough energy strikes the semiconductor in a solar cell, it frees an electron, which flows as current. One panel receives 1000 W of sunlight and delivers 200 W of electrical power.
What is the efficiency of the panel?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. Which model of light best explains how a solar cell frees electrons?
C2. Substitute numerical values into a mathematical representation that can be used to determine the electrical energy, in joules, that the panel delivers in 5.0 hours (18,000 s) of full sun. Then calculate the energy.
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C4. The silicon in the solar cell needs at least 1.1 eV (1.76 × 10−19 J) to free an electron. Determine the longest wavelength of light, in nanometers, that can free electrons in the cell.
C5. Why do solar cells produce no current in very long-wavelength infrared light?
C6. A town is deciding whether to replace part of its coal-fired electricity with rooftop solar panels like this one. Identify one benefit and one drawback of this choice.