Frequency vs. Intensity

[cadytran1K]

Hi! In the lecture, Dr. Lavelle mentioned that high intensity light would not emit electrons, but higher frequency light would. What's the difference between frequency and intensity?

[Sid Panda 3A]

Hi! In the lecture, Dr. Lavelle mentioned that high intensity light would not emit electrons, but higher frequency light would. What's the difference between frequency and intensity?

If you are talking about light as particles (photons), increasing the intensity of light only increases the number of photons. It does not not increase the energy of those photons in the light; there are just more photons hitting the surface of the metal without ejecting any electrons .

When you are talking about light as a wave, increasing the frequency leads to an increase of energy of the light itself. This is because of the equation E=h*v, where h is planck's constant and v is the frequency of the light.


Hope this helps!

[AnnaNovoselov1G]

Intensity corresponds to the amplitude of the wave (how high it is). It is defined as the distance from the crest or trough of a wave to the baseline (center line). For a classical wave, an increase in amplitude would correspond to an increase in energy.

Frequency, on the other hand, is the number of wavelengths that pass in some units of time. A wavelength is a full cycle of a wave (for instance, from crest to crest). Usually, it's measured in Hertz, or cycles per second.

The surprising result was that increasing the intensity of light didn't result in emitted electrons because this increase didn't correspond to increased energy! This led to the hypothesis that light behaves as a stream of particles (photons). On the other hand, increasing the frequency did result in increased energy and the emission of electrons (as shown by the equation E=frequency x planck's constant.

One key thing to remember is that increasing the intensity would cause more electrons to be emitted only if the energy of a single photon is enough to emit one electron.

[Pranav Daggubati 3C]

The short way of saying it is that you cant emit electrons if you don't have the right energy (frequency), even if you do have an enormous amount of photons (intensity)

[Kelly Yun 2I]

No matter how many photons there are (high intensity), if each photon does not have enough energy, electrons won't be emitted. Simply, if there's a certain threshold that must be passed for something to happen, having tons of things just under that threshold won't cause anything to occur.

[Ethan Laureano 3H]

I liked the analogy Dr. Lavelle gave in his lecture. It is sort of like a cross country team. No matter how many members you have, if not one of them can jump the hurdle, the team is not going to win.

[manisha_joseph_1H]

The intensity of light refers to the number of photons. Therefore, increasing the intensity of the light would increase the number of photons. However, in the case of the photoelectric experiment, the photons need to have a specific energy which is greater than or equal to the energy of the electron it is trying to eject. To increase the energy in the photon, the frequency of light must be increased because this corresponds with a higher energy level overall.

[vanessanguyen3I]

I am going to explain this in terms of the photoelectric effect.

To increase intensity is synonymous to making the light brighter. In a classical wave, the larger the amplitude of the wave, the more intense the light is. In a classical model, increasing the intensity of the light would increase the energy.

However, in the photoelectric effect, increasing the intensity of the light did not result in more electrons being ejected. From this experiment we learned that light does not just have wave properties. We need to think of light as consisting of packets of energy or photons. There is a one to one interaction between photons and electrons. In order to eject electrons, we need to change the frequency of the light (the frequency is the amount of cycles per second), which meant we needed to change the type of light (going from visible light to UV radiation).

Hope this helps.

[Vince Li 2A]

Light needs to be at a certain "frequency" in order to meet the threshold to eject electrons from the metal. If the light is not that frequency, then you can not eject electrons. However, suppose that the frequency meets the threshold energy, and electrons are ejected, then you can increase the "intensity" of the light, in other words you can add more light particles of that frequency to eject more electrons. What you should be cautious of is if the light does not meet the threshold for ejecting electrons, then increasing the intensity of the light wont' do anything.

Basically, frequency is how many waves are in one second, and intensity can be measured by the amount of light particles, all in terms of the photoelectric effect.

[Tae Pasawat 2A]

Intensity can be seen as the brightness of the light. This brightness is constituted by the number (quantity) of photons. The energy of light is seen as the color of the light itself, and not the brightness. A different color means that each individual photon has a different energy level. So a different color light of a higher energy but with a lower brightness (intensity) can still remove an electron from a metal!

[Margaret Xu 3C]

According to the equation E_photon = hv, we see that the energy of a photon is directly proportional to the frequency of light. Therefore, if the frequency increases, the energy of the photon increases, allowing electrons to be ejected. However, increasing the intensity of light only increases the number of photons. Even if you have multiple photons (high intensity), they won't be ejected if they don't have the energy required to overcome the work function.

[Chudi Onyedika 3A]

Light intensity is proportional to the number of photons. Light frequency is the number of waves that passes a point within a certain amount of time.

[Olivia Monroy 1A]

Light intensity is the number of photons hitting the surface, while frequency is the number of waves. Frequency determines if the energy is high enough to emit electrons in the photoelectric effect. If you have a high intensity, but the energy is not at or above the threshold then no electrons will be emitted.

[Zainab Jamali 1H]

In short, intensity is how many photons are hitting the metal surface while frequency influences the actual energy of the light. This is why frequency is key to the photoelectric effect: the energy of the light (affected by the frequency (E = h*v)) has to be greater than or equal to the threshold energy of the electrons on the metal's surface.

[Joshua Chung 2D]

The light must meet a certain frequency in order to eject electrons from the material. Since the intensity only refers to the number of photons and not their energy level, increasing the intensity but not the frequency will not affect whether or not electrons are ejected.

[Linette Choi 3L]

Higher intensity would only make the light brighter and increase the number of photons, not increase the energy of each individual photon. However, increasing frequency would increase the energy of the photons, allowing them to be able to eject the electrons.

[Dane_Beasley_1E]

Increasing the intensity will only increase the number of photons, but not the energy. So increasing intensity will not give it enough energy to eject electrons. However, increasing the frequency will increase the energy of the photon. Therefore, increasing frequency can give it the energy needed for an electron to eject.