What is h in e hf

Energy E is related to this constant h, and to the frequency f of the electromagnetic wave. This frequency is in the infrared range, so we could not see these photons with our eyes. And this enegy may be radiated in the form of photons or by heat or any other form.

In computational physics and chemistry, the Hartree—Fock HF method is a method of approximation for the determination of the wave function and the energy of a quantum many-body system in a stationary state. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Now we can determine the dimension of RC by the dimensions of resistance R and capacitance C.

Begin typing your search term above and press enter to search. Press ESC to cancel. Ben Davis February 26, What is H in E HF? Is equal to HF? What are the units of E in E HF?

Who proposed E HF? Can you use E HF for electrons? One common use of the photoelectric effect is in light meters, such as those that adjust the automatic iris on various types of cameras.

In a similar way, another use is in solar cells, as you probably have in your calculator or have seen on a roof top or a roadside sign. These make use of the photoelectric effect to convert light into electricity for running different devices. Figure 1. The photoelectric effect can be observed by allowing light to fall on the metal plate in this evacuated tube. Electrons ejected by the light are collected on the collector wire and measured as a current.

A retarding voltage between the collector wire and plate can then be adjusted so as to determine the energy of the ejected electrons. For example, if it is sufficiently negative, no electrons will reach the wire. This effect has been known for more than a century and can be studied using a device such as that shown in Figure 1. This figure shows an evacuated tube with a metal plate and a collector wire that are connected by a variable voltage source, with the collector more negative than the plate.

When light or other EM radiation strikes the plate in the evacuated tube, it may eject electrons. If the electrons have energy in electron volts eV greater than the potential difference between the plate and the wire in volts, some electrons will be collected on the wire.

Since the electron energy in eV is eV , where q is the electron charge and V is the potential difference, the electron energy can be measured by adjusting the retarding voltage between the wire and the plate. The voltage that stops the electrons from reaching the wire equals the energy in eV. For example, if —3. The number of electrons ejected can be determined by measuring the current between the wire and plate.

The more light, the more electrons; a little circuitry allows this device to be used as a light meter. What is really important about the photoelectric effect is what Albert Einstein deduced from it. Einstein realized that there were several characteristics of the photoelectric effect that could be explained only if EM radiation is itself quantized : the apparently continuous stream of energy in an EM wave is actually composed of energy quanta called photons.

In his explanation of the photoelectric effect, Einstein defined a quantized unit or quantum of EM energy, which we now call a photon , with an energy proportional to the frequency of EM radiation. It is the quantization of EM radiation itself. EM waves are composed of photons and are not continuous smooth waves as described in previous chapters on optics. Their energy is absorbed and emitted in lumps, not continuously. We do not observe this with our eyes, because there are so many photons in common light sources that individual photons go unnoticed.

See Figure 2. The next section of the text Photon Energies and the Electromagnetic Spectrum is devoted to a discussion of photons and some of their characteristics and implications. For now, we will use the photon concept to explain the photoelectric effect, much as Einstein did.

Figure 2. An EM wave of frequency f is composed of photons, or individual quanta of EM radiation. Higher intensity means more photons per unit area. The photoelectric effect has the properties discussed below. Some of these properties are inconsistent with the idea that EM radiation is a simple wave. For simplicity, let us consider what happens with monochromatic EM radiation in which all photons have the same energy hf.

Figure 3. Photoelectric effect. A graph of the kinetic energy of an ejected electron, KE e , versus the frequency of EM radiation impinging on a certain material. There is a threshold frequency below which no electrons are ejected, because the individual photon interacting with an individual electron has insufficient energy to break it away.

Einstein gave the first successful explanation of such data by proposing the idea of photons—quanta of EM radiation. It is a far more general concept than its explanation of the photoelectric effect might imply.

All EM radiation can also be modeled in the form of photons, and the characteristics of EM radiation are entirely consistent with this fact. As we will see in the next section, many aspects of EM radiation, such as the hazards of ultraviolet UV radiation, can be explained only by photon properties.

More famous for modern relativity, Einstein planted an important seed for quantum mechanics in , the same year he published his first paper on special relativity. His explanation of the photoelectric effect was the basis for the Nobel Prize awarded to him in Although his other contributions to theoretical physics were also noted in that award, special and general relativity were not fully recognized in spite of having been partially verified by experiment by Although hero-worshipped, this great man never received Nobel recognition for his most famous work—relativity.

What is the maximum kinetic energy of electrons ejected from calcium by nm violet light, given that the binding energy or work function of electrons for calcium metal is 2. The energy of this nm photon of violet light is a tiny fraction of a joule, and so it is no wonder that a single photon would be difficult for us to sense directly—humans are more attuned to energies on the order of joules.

But looking at the energy in electron volts, we can see that this photon has enough energy to affect atoms and molecules. A DNA molecule can be broken with about 1 eV of energy, for example, and typical atomic and molecular energies are on the order of eV, so that the UV photon in this example could have biological effects. The ejected electron called a photoelectron has a rather low energy, and it would not travel far, except in a vacuum.

The electron would be stopped by a retarding potential of but 0. In fact, if the photon wavelength were longer and its energy less than 2.