# Modern physics - photon problems

• avantgarde_
In summary, the work function of copper is about 4.7eV. This means that a photon with a minimum frequency of 1.136 x 10^15 Hz is needed to knock an electron out of a copper target. If a photon with 3 times the minimum frequency is used, the fastest electrons will leave the copper with a speed of 1.8 x 10^6 m/s and an extra kinetic energy of 9.4eV. This problem involves the photoelectric effect and can be solved using the equation hv - W = K, where h is Planck's constant, v is the photon frequency, W is the work function of the metal, and K is the kinetic energy. For the
avantgarde_
Anyone know how to go about solving the following two problems?

- What is the minimum frequency photons need to knock an electron out of a copper target?

- If a beam of photons with 3 times the frequency of the photons from the first problem strikes a copper target, at what speed will the fastest electrons leave the copper?

Thank you.

The Work Function of Copper

About 4.7eV. This means that a photon with a minimum frequency of 1.136 x 10^15 Hz {([4.7eV x 1.6022x10^(-19) J/eV] / h ) where h = 6.626 x 10^(-34) Js} is necessary. Energetic photon!

If a photon with a frequency = 3X the necessary frequency is incident, then the electron will be ejected with 9.4eV (3 x 4.7eV - 4.7eV) of K.E.

This corresponds to a speed of about 1.8 x 10^6 m/s. Approaching relativistic speeds...

Last edited:
This problem has to do with the photoelectric effect.

The equation to use is

hv - W = K

h is Planck's constant, v is the photon frequency. hv is the photon energy.

W is the work function of the metal, which is ~4.7 eV (7.5 x10^-19 J) for copper.

K is the kinetic energy.

In question 1 you are asking about a threshold energy, where are photon has just enough energy to kick the electron out of the copper, but give it no extra kinetic energy. K = 0 => hv = W

question 2, you are asking for the extra kinetic energy given a more energetic incident photon.

You can read more at http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html#c2

Cheyne

1)For your first question, you nedd to know abou the work function of copper, once you have that, you can equate it with hv where v=frequency of light striking the copper.

2)Now as per photoelectric effect , the total energy of the photon striking ..uses some of its energy to strike out the electron out of copper and rest conveerts into the KE of the ejected electron beam.

Therefore use hv=work Function+ Kinetic energy of electron Beam

## 1. What is a photon?

A photon is a fundamental particle that is the basic unit of light and all other forms of electromagnetic radiation. It carries energy and has no mass, and it behaves both as a particle and as a wave.

## 2. How is the energy of a photon calculated?

The energy of a photon is calculated using the equation E = hf, where E is the energy, h is Planck's constant, and f is the frequency of the photon. This means that the energy of a photon is directly proportional to its frequency.

## 3. Can photons be created or destroyed?

Photons cannot be created or destroyed. They can only be converted into other forms of energy or absorbed by matter, causing it to emit another photon.

## 4. What is the dual nature of a photon?

The dual nature of a photon refers to its ability to behave as both a particle and a wave. This is known as wave-particle duality and is a fundamental concept in modern physics.

## 5. How do photons interact with matter?

Photons can interact with matter in several ways, including absorption, reflection, and transmission. When a photon is absorbed by an atom, it can cause an electron to jump to a higher energy level. When a photon is reflected, it bounces off the surface of an object. When a photon is transmitted, it passes through an object without being absorbed or reflected.

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