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How to Calculate the Work Function of a Metal

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What is Work Function?

Definition of work function: The work function of a metal is the minimum amount of energy that is needed to eject an electron from the surface of a metal. The unit of work function electronvolt (eV) or Joules(J). The symbol for the work function is Φ or W. Understanding how to calculate the work function is very important in various areas of physics, such as quantum mechanics and material science.

Video Explanation: How to Calculate the Work Function

In physics, the work function is an important concept that relates to the energy required to remove an electron from a solid surface. Watch the video below for more explanation and a few solved problems:

This article will guide you through the process of calculating the work function, step by step, providing a clear understanding of this fundamental concept.

Work function formula: how to calculate work function of a metal
How to Calculate the Work Function of a Metal

Additionally, the work function, denoted as φ (phi), represents the minimum amount of energy required to remove an electron from a solid material. It is a material-specific property that depends on factors such as the type of material, its crystal structure, and the presence of impurities. The work function is typically measured in electron volts (eV) or joules (J).

The work function of a metal measures the minimum amount of energy that can liberate an electron from the surface of that metal.

Work Function Formula and Video Explanation

The formula for calculating the work function are:

  1. The first formula for calculating work function is Φ = E + K.E [where Φ = work function, E = total energy, and K.E = Maximum kinetic energy of liberated photoelectrons]
  2. We also have Φ = hf0 [where w = work function of the metal, h=Planck’s constant, and f0=Threshold frequency]
  3. The third formula for work function is Φ = hc/λ [where h=planck’s constant, c= speed of light in the vacuum, and λ=wavelength of the radiation]. This is because f=c/λ, and since Φ = hf, this implies that Φ = hc/λ

Photoelectric Equation

To comprehend the concept of work function better, it is essential to look into the phenomenon known as the photoelectric effect. The photoelectric effect occurs when light, typically in the form of photons, strikes the surface of a material and causes the ejection of electrons.

Definition of Photoelectric Effect: The photoelectric effect is due to the emission of electrons from the surface of a metal when light is shown on it. We can write the photoelectric equation as

E = hf = Φ + (1/2)mv2

Where

E = energy required to liberate an electron from the surface of a metal

h = Planck’s constant

f = This is the frequency

Φ = This symbol represents the work function

m = mass of an electron

Einstein’s Explanation

Albert Einstein provided a groundbreaking explanation of the photoelectric effect by proposing that light energy is quantized into discrete packets called photons. The energy of a photon is directly proportional to its frequency, and when a photon interacts with a material, it transfers its energy to an electron, enabling its release from the surface.

How to Calculate the Work Function of a Metal

Calculating the Work Function

To calculate the work function, you need to follow a step-by-step process:

Step 1: Determine the Energy of the Incident Photon

The energy of a photon is given by the equation E = hf, where E represents energy, h is Planck’s constant (approximately 6.626 x 10-34 J·s), and f denotes the frequency of the photon.

Step 2: Calculate the Kinetic Energy of the Ejected Electron

The kinetic energy (KE) of the ejected electron can be determined using the equation KE = hf – φ, where φ is the work function of the material.

Step 3: Calculate the Work Function

Rearranging the equation from Step 2, we can determine the work function as φ = hf – KE.

Applicable Methods of Finding Work Function of a Metal

Method 1: Calculating the Work Function of a Metal Surface

Suppose we have a metal surface that is struck by a photon with a frequency of 2.5 x 1014 Hz. The kinetic energy of the ejected electron is measured as 4.0 x 10-19 J. By substituting the given values into the equation φ = hf – KE, we can calculate the work function.

φ = hf – KE = (6.626 x 10-34 x 2.5 x 1014) – 4.0 x 10-19 = -2.3435 x 10-19

Example 2: Calculating the Work Function of a Semiconductor

In the case of a semiconductor material, the process of calculating the work function is similar to that of a metal surface. However, semiconductors exhibit unique characteristics due to their energy band structure, which affects electron behavior.

Solved Problems: How to Calculate the Work Function of a Metal

Here are a few examples to help you understand how to calculate the work function of a metal.

Problem 1

A metal is illuminated with radiation of energy 6.88eV. If the kinetic energy of the emitted electrons is 1.5eV. Calculate the work function of the metal.

How to calculate work function of a metal
Picture solution

Text Solution

Data:

The work function, Φ = Total energy + Kinetic energy

and the the incident radiation = total energy = 6.8eV

The kinetic energy of the emitted electron = 1.5eV

and the formula is Φ = E + K.E

Thus,

Work function, Φ = 6.8eV + 1.5eV = 8.4eV

Problem 2

A metal was exposed to photons at a frequency of 2.0 x 1015Hz, and electrons were emitted with a maximum kinetic energy of 4.00 x 10-19 J. Calculate the work function, of this metal.

How to Calculate the Work Function
picture solution

Text Solution:

Data:

Φ = hf + K.E

and

Frequency of photons, f = 2.0 x 1015Hz

The maximum kinetic energy of the electron, K.E = 4.00 x 10-19 J

planck’s constant, h = 6.6×10-34Js

Hence, we can now apply the formula for the work function that says Φ = hf + K.E

Thus, we now have Φ = (6.6×10-34) x (2.0 x 1015) + (4.00 x 10-19)

This is equal to

Φ = (6.6×10-34) x (2.0 x 1015) + (4.00 x 10-19)

we now have

Φ = 1.32×10-18 + 4.00 x 10-19

Therefore, the work function Φ, of the metal is 1.72 x 10-18 J

Problem 3

When metal was exposed to photons at a frequency of 1.10 x 1015Hz, electrons were emitted with a maximum kinetic energy of 4.00 x 10-19J. Calculate the work function of the metal.

Work Function Problem
Picture solution

Text Solution

Data:

frequency, f = 1.10 x 1015Hz

Maximum kinetic energy, K.E = 4.00 x 10-19J

The work function of the metal, Φ =?

Planck’s constant, h = 6.6×10-34Js

Therefore, by applying the formula for the work function that says Φ = hf + K.E

After substituting our data into the above formula for the work function, we will now have

Φ = (6.6×10-34) x (1.10 x 1015) + (4.00 x 10-19)

After multiplying (6.6×10-34) by (1.10 x 1015) the above expression will give us

Φ = (7.26×10-19) + (4.00 x 10-19)

We will now add (4.00 x 10-19) to (7.26×10-19), Which implies that the above expression is now

The work function of the metal, Φ = 1.126×10-19J

Therefore, the work function of the metal Φ is 1.126×10-19J

Problem 4

Calculate the work function of a metal in eV, if its threshold wavelength is 6,800Å [Take h = 6.6 x 10-27 ergs].

How to Calculate the Work Function of a Metal
Image Solution

Text Solution

Data:

The wavelength, λ = 6,800Å

and from our knowledge of prefixes, the symbol Å is called angstrom, and 1Å = 0.0000000001 or 10-10m

Thus, the wavelength, λ = 6,800Å = 6,800 x 10-10m = 6.86 x 10-6m

Therefore, λ = 6.86 x 10-6m

From the above question, we were told that Planck’s constant, h = 6.6 x 10-27 ergs = 6.6 x 10-27 x 10-7 [This is because 1 erg is equal to 10-7J]

Therefore we can now write Planck’s constant, h = 6.6 x 10-27 x 10-7 = 6.6 x 10-27-7 = 6.6 x 10-34Js

Solution (applying data and the work function formula)

We will apply the formula for the work function, which is Φ = hc/λ [where h=planck’s constant, c= speed of light in the vacuum, and λ=wavelength of the radiation]

Speed of light in the vacuum, c = 3 x 108 m/s

After substituting our values into the above formula, we will have

Φ = (6.6 x 10-34 x 3 x 108)/6.86 x 10-6

We multiply the numerator (6.6 x 10-34 x 3 x 108) to obtain 1.98 x 10-25

Thus,

Work function, Φ = 1.98 x 10-25/6.86 x 10-6

Dividing 1.98 x 10-25 by 6.86 x 10-6 will give us 2.886 x 10-20

Work function, Φ = 2.886 x 10-20J

Which explains that the work function of the metal is 2.886 x 10-20J

To convert our answer into electronvolt, we consider 1eV = 1.6 x 10-19J

Hence, Work function, Φ = (2.886 x 10-20J x 1eV) / 1.6 x 10-19J = 0.179125eV

Therefore, our work function in electronvolt, Φ = 0.179125eV or approximately into 0.2eV

Further Explanation on Work Function

Work function is very important in various fields, including semiconductor devices, solar cells, and vacuum electronics. Thus, the energy from the work function can be supplied through thermal excitation, electrical bias, or electromagnetic radiation. In essence, the work function is the energy required to overcome the potential barrier that holds the electrons within the material’s surface. Additionally, the work function is measured in electron volts (eV) and is denoted by the symbol Φ.

The Importance of the Work Function

Work function is an excellent parameter in determining the electronic properties of materials. For instance, we use work function to understand the electronic behavior of metals, semiconductors, and insulators. Moreover, the work function is also important in determining the efficiency of electronic devices. Some of these devices are photovoltaic cells, field-effect transistors, and thermionic converters.

Factors Affecting the Work Function

It is also important to know that several factors can influence the work function of a material. These factors include:

  1. The surface orientation,
  2. Crystallographic structure,
  3. Temperature, and
  4. Doping.

For instance, the work function of a metal surface may vary depending on the crystallographic orientation of the surface. Doping, on the other hand, involves the intentional introduction of impurities into the material. Hence, this action can alter the electronic properties of the material, including the work function.

Other Methods of Calculating the Work Function

We can apply different approaches to calculate the work function of a material. Some of these approaches include:

1. The Photoelectric Effect

The photoelectric effect involves the emission of electrons from a material’s surface when exposed to electromagnetic radiation. Therefore, we can use the energy of the incident radiation to determine the work function of the material.

E = hf = Φ + (1/2)mv2

2. The Richardson-Dushman Equation

When we talk of the Richardson-Dushman equation. We are relating the current density of a heated metal surface to the temperature and the work function. This equation can be used to determine the work function of a metal. The mathematical expression of the Richardson-Dushman equation is

Je = A T2 exp(-Φ/kT)

Where

A = Richardson -Dushman Constant

Je = Current density due to the emission

k = Boltzman constant

T = temperature of the emission

Φ = work function

3. The Kelvin Probe Method

The Kelvin probe method involves measuring the potential difference between a metal surface and a reference electrode. This potential difference can be used to determine the work function of the metal.

C=Q/V=(ε. A)/t

C = capacitance

Q = charge

V = Potential difference

ε = Permittivity of the dielectric

A = Surface area of the capacitor

t = time taken

Applications of the Work Function

The work function formula finds numerous applications in various fields. For instance, we use the work function to understand the electronic properties of materials in the semiconductor industry. Additionally, It is also a parameter in determining the efficiency of photovoltaic cells. In vacuum electronics, the work function is used to understand electron emission from hot cathodes.

Frequently Asked Questions (FAQs)

What is the work function?

The work function formula refers to the energy needed to remove an electron from a solid material’s surface and is measured in electron volts (eV).

What factors affect the work function of a material?

Several factors can influence the work function of a material, including surface orientation, temperature, doping, and crystallographic structure.

What is the work function and threshold frequency formula?

The formula for work function and threshold frequency is E = hf = Φ + (1/2)mv2

What is the work function unit?

The s.i unit of the work function is in Joules

What is work function formula in Terms of wavelength?

The work function formula in Terms of wavelength is Φ = hc/λ

we can also use the formula E = hc/λ + (1/2)mv2

More Videos: Work Function

Work Function

Photoelectric Effect

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How to Calculate Threshold Frequency

How to Calculate Power in a Circuit

Reference

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