Question
Use the frequency ranges in the table to answer the question.
Frequency ranges for ultraviolet and infrared radiation
| Ultraviolet | 3.0 × 10^16 Hz to 7.5 × 10^14 Hz |
|---|---|
| Infrared | 4.3 × 10^14 Hz to 3.0 × 10^11 Hz |
Based on the information in the preceding table, which TWO of the following comparisons about ultraviolet and infrared light are true?
A. Ultraviolet light has shorter wavelengths than infrared light does.
B. Ultraviolet light has longer wavelengths than infrared light does.
C. Photons of ultraviolet light have less energy than photons of infrared light do.
D. Photons of ultraviolet light have more energy than photons of infrared light do.
Answer
The correct choices are A and D.
All electromagnetic waves travel at the same speed in vacuum, so
The ultraviolet frequencies in the table are higher than the infrared frequencies. Because wavelength is inversely proportional to frequency, ultraviolet light has the shorter wavelength. This makes A true and B false.
The energy of one photon is
where is Planck's constant. Photon energy increases with frequency, so an ultraviolet photon has more energy than an infrared photon in the listed ranges. This makes D true and C false.
The energy comparison is per photon. A beam's total energy also depends on how many photons it contains.
Evidence boundary
This answer compares the frequency ranges shown in the question, the corresponding vacuum wavelengths, and energy per photon. It does not compare beam intensity, total beam energy, photon count, biological effects, or any particular source of ultraviolet or infrared radiation.
Sources
These references support the concepts and methods used in the explanation above.