Electromagnetic Field: EMF, Continuous and Discrete Structure, Sources

An electromagnetic field is a physical field extending throughout space that is produced due to the combined effect of electric and magnetic fields. Charges at rest are the source of the electric field but moving charges are the source of both electric and magnetic fields. 

• A changing electric field can also be produced by a changing magnetic field.
• The mutual interaction of these two fields produces an electromagnetic field.
• A charge or current interacts with an electromagnetic field according to Maxwell's equations and Lorentz's force law.
• The study of the interaction that occurs between particles with electric charge via electromagnetic fields is known as Electromagnetism.
• Many household appliances like Mobile phones, microwave ovens, and computer screens produce electromagnetic fields.

Read Also:- Continuous Charge Distribution

Key Terms:- Charge density, Sources of Charge, electric field, surface charge density, Field lines, Magnetic field, Electric Charges, Frequency, Maxwell's equations, Lorentz's force law, Electromagnetism, Electromagnetic field

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Electromagnetic Field

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The combined effect of electric and magnetic fields is called an electromagnetic field, which is produced by the motion of the charges.​

• The force due to an electromagnetic field is called electromagnetic force, and it is one of the four fundamental forces in nature.
• The other fundamental forces are Gravitational force, Strong nuclear, and Weak nuclear force.
• The electromagnetic field is generated both by natural phenomena and also by human activities.
• According to classical physics, the electromagnetic field can be regarded as a smooth, continuous field, propagated in a wavelike manner.
• Whereas, according to quantum field theory, this field is seen as quantized.
• There are certain circumstances in which this electromagnetic field can be described as a wave that transports electromagnetic energy.

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Electromagnetic Field Structure

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The electromagnetic field contains both the electrical and magnetic components which manifest as a field of force. Its structure can be viewed in two different ways i.e. continuous and discrete structure. The explanation of both the structure has been mentioned below:

Continuous Structure

In classical physics, electric and magnetic fields are thought to be produced by the smooth motion of charged particles.

• Considering the example of oscillating charges producing changes in the electric & magnetic fields which can be observed in a 'smooth', continuous, and wave-like fashion.
• In the following situation, the energy is observed as being continuously carried through the electromagnetic field within any two locations.
• This view is useful to a particular extent i.e. for radiation of a low frequency, but the problems are found at higher frequencies.

Electromagnetic wave

Discrete Structure

According to the studies, in a few of the circumstances, the transfer of electromagnetic energy is better described as being carried in the form of packets called “quanta” with a fixed frequency.

• A quantum i.e. singular form of quanta, is the minimum amount of any physical entity involved in an interaction.
• A photon is a single quantum of light of a specific frequency or any other form of electromagnetic radiation.
• Planck's relation links the photon energy ‘E’ of a photon to its frequency ‘f’ through an equation mentioned below:

E = hf

          Where h is Planck’s constant and f is the frequency of the photon.

• This quantum picture of the electromagnetic field has proven very successful, giving rise to quantum electrodynamics and a quantum field theory.
• It also gives rise to quantum optics.

Discrete Structure

Read Also:- Unit of Electric Field

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Sources of Electromagnetic Fields

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Electromagnetic fields exist everywhere in our environment including our homes, workplaces, and schools.  Electromagnetic fields are generated either by natural or man-made sources.

Sources of Electromagnetic Fields

Natural Sources

When it comes to natural sources, the EM field can be observed almost everywhere in the environment we live in. Natural sources of electric and magnetic fields include:

• The magnetic field of the earth; makes a compass point north and is used as a navigation for birds and fishes.
• The electric field is produced due to the electric charge present in the environment associated with the thunderstorms.
• Visible light

Earth’s Magnetic Field

Man-Made Sources

Unlike natural resources, the man-made sources of electromagnetic fields include the energy which is generated through man-made sources. A few of the man-made sources of electromagnetic fields include:

• X-rays; used to look at the bones and joints of a human body
• Electrical Appliances like vacuum cleaners, hair dryers, and refrigerators 
• Electricity passes through the power socket.
• Radio Communications Devices like radio and television, air traffic control, remote controls, and mobile phones.

Man-Made sources of electromagnetic fields

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Difference between Magnetic Field and Electric Field

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The difference between the electric and magnetic fields has been explained in the table below:

Also Check:- Verify the laws of parallel combination of resistances using a metre bridge experiment

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Human Exposures to Electromagnetic Field

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Exposures of human to electromagnetic field is not a new phenomenon. Nowadays electromagnetic fields in our surroundings increasing as growth in the electricity demand, advancing technologies, and artificial sources.

• We are all exposed to electromagnetic fields daily, whether we are at work or home, due to the generation and transmission of electricity, the use of household appliances, industrial equipment, telecommunications, or broadcast, among others.
• A small electric current exists in the human body due to chemical reactions.
• External electromagnetic fields induce voltages and currents in the body.
• The induced currents are very small compared to thresholds for producing shock and other electrical effects.
• Heating is the main biological effect of the electromagnetic fields. In microwave ovens, this fact is employed to warm up food.
• People are normally exposed to very low levels of radiofrequency fields, which are insignificant in comparison to those required to produce significant heating.
• As of yet, no adverse health effects have been confirmed from low-level, long-term exposure to radiofrequency or power frequency fields, but scientists are actively researching this subject.

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Previous Year Questions 

1. Charge is a…… [KEAM]
2. The maximum torque exerted by the field on the dipole is….
3. A plane square sheet of charge of side 0.5m  has uniform surface charge ….. [KEAM]
4. After initial contact and separation, each sphere will be having….​.
5. What is the relation between qq and QQ if the two parts, when placed apart, has maximum coloumb repulsion….​.

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Things to Remember

• The ElectroMagnetic field propagates at the velocity of light.
• It can interact with the charges & currents.
• It’s a form of energy produced due to the movement of charged particles.
• It can also be expressed as a wave transporting electromagnetic energy.

Read Also:- Electric Charges and Fields