A wave machine's crests are raised to three times their height, with the medium, wavelength, and speed unchanged. What happens to the energy the waves carry?
A dim lamp shines on a zinc plate. Imagine the light as the waves topic drew it: a continuous electromagnetic wave, washing over the whole surface at once. Every electron in the plate sits under that steady wash, receiving energy.
Light is a wave; that model earned its place with evidence. Before this topic judges the wave model against the four observations, the model's own prediction has to be stated fairly. This lesson states it.
In the waves topic, you saw that a wave's amplitude determines the energy it carries.
For light in the wave model, a bigger amplitude means a more intense, brighter light.
The wave washes over the whole surface at once, so every electron receives a share of the arriving energy.
An electron's share builds up: energy keeps arriving, second after second, and the electron can accumulate it.
On this prediction, light of any frequency should eventually eject electrons, if it is intense enough or shines long enough.
A dim light wave would slowly build up enough energy at each electron in a zinc plate; the ejection would start late, but it would start.
You have also seen, in the electromagnetic waves topic, that higher-frequency electromagnetic waves carry more energy.
The pure wave model cannot use the higher frequency's extra energy here: in this model, the energy delivered to the plate is set by the brightness and the exposure time, not by the frequency.
So within the wave model, frequency should never decide whether electrons come out; only brightness and time should matter.
Red light of low intensity shines on a clean zinc plate. What does the wave model predict?
In the wave model, the light's energy arrives continuously and spreads across the whole surface.
Each electron accumulates its share of the arriving energy over time.
Low intensity and low frequency only slow the build-up; in this model they do not stop it.
The wave model predicts that the red light will eventually eject electrons from the zinc, after a long enough wait.
Under the wave model, how could a lamp that has ejected nothing so far be made to eject electrons, without changing its frequency?
In the wave model, the energy delivered is set by the brightness and the exposure time.
Raising the intensity delivers more energy to each electron every second.
Shining for longer lets each electron accumulate more energy.
On the wave model's prediction, raising the intensity or simply waiting longer should eventually bring ejection.
Under the wave model, dim light shines on a metal plate. How does the light's energy reach one electron in the plate?
A lamp has ejected nothing from a metal plate so far. Under the wave model's prediction, what could make the light eject electrons, with its frequency unchanged?
Una says: 'In the wave model, a dim light can make up for its dimness by shining on the metal for longer.' Is Una correct?
Which statement is the wave model's prediction for light shining on a metal?
Under the wave model, why should even low-frequency light eventually eject electrons from a metal?
Higher-frequency electromagnetic waves carry more energy. In the pure wave model, which two things set the total energy delivered to a lit plate?