Electromagnetic Radiation

Electromagnetic Radiation

Introduction

Is the flow of energy at the universal speed of light through free space or through a material medium in the form of the electric and magnetic fields.

Visible light is one type of electromagnetic radiation, other familiar forms are invisible electromagnetic radiations such as X-rays and radio waves.

EMR consists of electromagnetic waves.

Electromagnetic radiation is a type of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays and gamma-rays.

Introduction

Electromagnetic Waves

Electromagnetic waves are waves oscillations of electric and magnetic fields that propagate at the speed of light.

The oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation.

The electric and magnetic fields in EMR waves are always in phase and at 90 degrees to each other.

Electromagnetic Waves

Electromagnetic Waves

The electromagnetic radiation are distinguished by frequency and wave length of their electromagnetic wave.

• Frequency is the number of complete cycles formed by a wave at a period of a second.
• The SI unit of frequency is Hertz (Hz) but also can be expressed as per second.

It is represented

Electromagnetic Waves

Wave length is the distance cover by a single complete cycle (frequency) of a wave.

Wave length is the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings The unit of wave length is Meter (M).

Wavelength is represented by lambda.

Sine Wave

Is a mathematical curve that describes a smooth repetitive oscillation.

The sine wave is important in physics because it retains its wave shape when added to another sine wave of the same frequency and arbitrary phase and magnitude.

• It is the only periodic waveform that has this property.

Electromagnetic waves are also a sine wave.

Sine Wave

Electromagnetic Spectrum

Is the range separation of Electromagnetic radiation according to their frequency and wave length.

The electromagnetic radiation classified as; radio waves, microwave, infrared rays, visible light, ultraviolet rays, X-rays and gamma rays.

Although all electromagnetic waves travel at the speed of light in a vacuum, they do so at a wide range of frequencies, wavelengths, and photon energies.

Electromagnetic Spectrum

Visible Radiation

Light is the most familiar form of electromagnetic radiation and makes up that portion of the spectrum to which the eye is sensitive.

The corresponding wavelengths extend from 7 × 10-5 centimeter (red) to 4 × 10-5 centimeter (violet).

Why visible radiation is important to our life?.

Wave-Particle Duality

Wave particle duality is the behavior of electromagnetic radiation that it exhibit both wave like nature and particle like nature.

• Electromagnetic radiation is usually thought of as being a wave.

How is it known that it behaves like a wave?

If visible light is considered, it can be demonstrated that visible light can undergo reflection, réfraction, diffraction, interference, etc., all of which are properties of waves.

Wave-Particle Duality

Particle – like properties

Some phenomena associated with electromagnetic radiation, such as the photoelectric effect and Compton scattering, cannot be explained by the wave theory.

To explain these phenomena, electromagnetic radiation must be considered to behave as particles or packets of energy rather than as waves.

Wave-Particle Duality

Wave-Particle Duality

Electromagnetic radiation is considered as particle since has mass and carries energy in quanta.

Since electromagnetic radiation has mass thus has momentum which can cause ejection of electron in an atom as in photoelectric effect or Compton effect.

From quantum physics E = h f……..1

Wave-Particle Duality

• From Einstein equation of relativity
• E= mc2…………2
• By equating equations 1 and 2
• mc2 =hf
• m=hf/c2
• where h is plank’s constant = 6.6×10-34j.s
• c is speed of light in space =3×108m/s

In a unit of kilogram

Types of EMR

• There are two main electromagnetic radiation according to their energy.
• Ionizing radiation

Non- ionizing radiation

Ionizing radiation are those radiation with ability to cause ionization of an atom such as X-rays, Gamma rays and Ultra violate radiation.

Non-ionizing radiation are those which have no ability to cause ionization of an atom such as radio waves and micro waves.

Types of EMR

Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atom or molecules. That is, to completely remove an electron from an atom or molecule.

Instead this electromagnetic radiation has sufficient energy only for excitation of electrons (the movement of an electron to a higher energy state.)

Uses of EMR

Some form of electromagnetic radiation are used in medical purpose such us in diagnosis of diseases on human body and also can be used as therapeutically as in radiotherapy.

Such electromagnetic radiation include X-rays, visible light and gamma rays.

This electromagnetic radiation have low wave length, high frequency and high energy which allows them to pass through human tissues.

The tendency of these wave to pass through human tissue, it help us to diagnose different pathological issues in our body.

Visible Light

This electromagnetic waves have longer wave length, thus does not penetrate through human tissue But it is useful in diagnosis and treatment procedures since it can be used to guide where the x-rays and gamma rays should be exposed during the diagnostic and therapeutic procedures.

Uses of EMR