Hamish wants a number. A single photon lands on a light sensor and delivers its whole lump. Exactly how much energy was that, in joules?
A photon's energy rises in proportion with frequency; that was the direction. This lesson presents the exact rule, which turns a frequency such as 5.0 × 10¹⁴ Hz into one photon's energy.
E is the photon's energy, measured in joules (J).
f is the light's frequency, measured in hertz (Hz).
h is a fixed number of nature, the same for every photon of every kind of light.
That fixed number is called Planck's constant, and its value is h = 6.63 × 10⁻³⁴ J·s.
You have met the letter h before: in the work and energy topic, h stood for an object's height. Here h is Planck's constant, not a height. Any problem that needs both writes 'height' out in words.
Multiplying the light's frequency by Planck's constant gives one photon's energy. That is all E = hf says. The multiplying itself is the next lesson's job; this lesson's job is the equation and its parts.
Which of these is the photon-energy equation: E = hf, E = h + f, or h = Ef?
A photon's energy rises in proportion with frequency, so the right form multiplies f by a fixed constant.
E = h + f adds unlike quantities; adding joule-seconds to hertz has no meaning.
h = Ef puts the fixed constant on the left as if it were the unknown; h never changes.
E = hf is the photon-energy equation.
In E = hf, which symbol carries the unit hertz, and which carries joules?
f is the light's frequency, so f carries hertz.
E is the photon's energy, so E carries joules.
h is Planck's constant, in joule-seconds, which ties the two together.
f is in hertz; E is in joules.
Which equation gives a photon's energy from the light's frequency?
In the equation E = hf, which quantity is measured in hertz?
The fixed number h in the photon-energy equation is called which of the following?
Which equation is the photon-energy relation?
Which line pairs each symbol in E = hf with its unit correctly?
A problem needs Planck's constant and a shelf's height at the same time. How is the height written?