Electromagnetic Radiation: Wave and Particle Models, Study notes of Radiation Quantities and Units

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ELECTROMAGNETIC RADIATION

Concept of Energy

• It is the ability to do work

• During work energy is transferred from one body to

another and from one place to another

• There are three ways in which energy can be

transferred

Definition

• (^) EMR consisting of self-sustaining oscillating electric and magnetic

fields at right angles to each other and to the direction of

propagation. It does not require a supporting medium and travels

through empty space at the speed of light

or

• (^) EMR is a form of energy emitted and absorbed by

charged particles which exhibits wave-like behavior as

it travels through space. It propagates as wave motion

at a velocity of c = 3 x 10

8

m/sec

Electromagnetic Radiation

Production of electromagnetic radiation and its

propagation through space and its interaction with

other matter is explained by using wave model and

particle model

The two fields are at right angles to each other and are perpendicular to the direction of propagation

1) Amplitude – this is “how high” the

wave is:

2) Wavelength (  _) – this is the distance between two corresponding points on the wave and is measured in metres:

3. Frequency – number of cycles of a wave passing a fixed point per unit time and is measured in Hertz (Hz)_ The parameters that characterize a wave motion are “amplitude (a), wavelength (λ) and frequency (γ)”

Electromagnetic Waves

• (^) A crest is the point on a wave with the maximum value or upward displacement within a cycle
• (^) A trough is the opposite of a crest, so the minimum or lowest point in a cycle

How do electromagnetic waves differ? Different electromagnetic waves carry different amounts of energy. For example, microwaves carry less energy that X-rays.  (^) The amount of energy carried by an electromagnetic wave depends on the wavelength: the shorter the wavelength , the higher its energy.  (^) Wavelength and frequency are linked properties of a wave: the shorter the wavelength , the higher its frequency.  (^) So, frequency also tells you about the energy of a wave: the higher its frequency , the higher the energy.

What happens when waves hit a surface?

When electromagnetic waves hit a surface, they can be reflected , absorbed or transmitted. The waves behave, depends on their energy and the type of material. For example: light waves are reflected by skin but X-rays pass straight through. If electromagnetic waves are absorbed, some of their energy is absorbed by the material. This usually increases the temperature of the material.

• (^) When matter excited thermally or by nuclear processes

or by bombardment with other radiation photons are

emitted

• (^) Photons move at the speed of light
• (^) Photons also exist as reflected or absorbed radiation
• (^) Amount of energy associated with a photon is

determined as Q=hv

• (^) h=Planck’s constant (6.626X

J)

EMR is both wave and a stream of particles