Electromagnetic Radiation and Electromagnetic Spectrum | X-ray physics | Radiology Physics Course #7

Summary

This script delves into the principles of electromagnetic force and radiation, illustrating how currents induce magnetism and vice versa. It introduces the electromagnetic spectrum, highlighting the inverse relationship between wavelength and frequency. The script explains the nature of visible light, infrared, microwaves, radio waves, ultraviolet, X-rays, and gamma rays, emphasizing the ionizing capability of the latter due to their high energy. It also discusses the structure of electromagnetic waves, their self-propagation at the speed of light, and their transverse movement. The concept of wave-particle duality is introduced, with the photoelectric effect exemplifying the particle-like behavior of electromagnetic waves. The script sets the stage for an X-ray physics module, offering a foundational understanding of the subject.

Takeaways

• 🌐 The electromagnetic spectrum is organized by wavelength and frequency, with wavelength increasing and frequency decreasing as you move up the spectrum.
• 🔄 Wavelength and frequency are inversely proportional, meaning as one increases, the other decreases.
• 👀 Visible light, which our eyes can see, is in the middle of the spectrum, ranging from about 700 nanometers to just below 400 nanometers.
• 🌈 The electromagnetic spectrum is divided into categories such as infrared, visible light, ultraviolet, X-rays, and gamma rays based on wavelength.
• 🚫 X-rays and gamma rays have high enough frequencies and energies to ionize atoms, making them ionizing radiation, unlike visible light.
• 🌊 Electromagnetic waves are transverse waves, with the direction of energy movement perpendicular to the wave itself.
• 🛰️ Electromagnetic waves, including radio waves and X-rays, travel at the speed of light in a vacuum, independent of their frequency or wavelength.
• 🌀 The structure of an electromagnetic wave is consistent across the spectrum; only the wavelength and frequency vary.
• 🤔 Electromagnetic radiation exhibits wave-particle duality, meaning it can act as both a wave and a particle, as demonstrated by the photoelectric effect.
• ⚡ The energy of an electromagnetic wave is directly proportional to its frequency and is quantized, as shown by the equation E = hν, where h is Planck's constant.
• 🔬 Understanding electromagnetic radiation is crucial for studying X-ray physics, as X-rays are a form of electromagnetic radiation.

Q & A

What is the relationship between the wavelength and frequency of electromagnetic waves?

The wavelength and frequency of electromagnetic waves are inversely proportional to each other. As the wavelength increases, the frequency decreases, and vice versa.

How is the electromagnetic spectrum oriented in the provided script?

The electromagnetic spectrum is oriented vertically in the script, with wavelength increasing as you move up the diagram and frequency decreasing.

What is the range of wavelengths for visible light within the electromagnetic spectrum?

Visible light ranges from about 700 nanometers to just below 400 nanometers, covering the spectrum from red to violet.

What are the categories of the electromagnetic spectrum based on wavelength?

The categories include visible light, infrared, microwaves, radio waves, ultraviolet light, X-rays, and gamma rays, each with different wavelength ranges.

Why are X-rays and gamma rays considered ionizing radiation?

X-rays and gamma rays have high enough frequencies and energies to release electrons from atoms, which is known as ionization.

What is the speed at which electromagnetic waves travel through a vacuum?

Electromagnetic waves travel through a vacuum at the speed of light, which is a constant speed for all types of electromagnetic radiation.

How does the amplitude of an electromagnetic wave relate to its intensity?

The amplitude of an electromagnetic wave represents its intensity, and it is generally proportional to the number of photons in the radiation.

What is the nature of electromagnetic waves in terms of their propagation?

Electromagnetic waves are self-propagating and transverse in nature, meaning the direction of energy movement is perpendicular to the wave movement.

What is the concept of wave-particle duality as it applies to electromagnetic radiation?

Wave-particle duality refers to the concept that electromagnetic radiation can exhibit properties of both waves and particles, as demonstrated by phenomena like the photoelectric effect.

How does the energy of an electromagnetic wave relate to its frequency?

The energy of an electromagnetic wave is directly proportional to its frequency, as described by the equation E = hν, where E is energy, h is Planck's constant, and ν is frequency.

What did scientists observe during the photoelectric effect experiment that supports the wave-particle duality of electromagnetic waves?

Scientists observed that even at the smallest intensity, increasing the frequency into the range of X-rays would release an electron from a metal sheet, indicating that the waves were acting as particles with discrete packets of energy and mass.

Outlines

00:00

🌌 Electromagnetic Radiation and the Spectrum

This paragraph introduces the concept of electromagnetic radiation and the electromagnetic spectrum. It explains how the movement of currents can induce magnetism and vice versa, leading to the generation of electromagnetic waves. The spectrum is depicted as a vertical diagram where wavelength increases and frequency decreases as we move up the scale. Visible light is situated in the middle of the spectrum, flanked by infrared and ultraviolet light, with X-rays and gamma rays at the high-frequency, short-wavelength end. The paragraph also touches on the wave-particle duality of electromagnetic radiation, emphasizing the quantized nature of energy and the photoelectric effect, which demonstrates the particle-like behavior of light.

05:02

🌐 The Nature of Electromagnetic Waves

The second paragraph delves deeper into the properties of electromagnetic waves, describing them as self-propagating transverse waves that do not require a medium for transmission, unlike ultrasound waves. It highlights the dual nature of electromagnetic radiation, which can be thought of as both waves and particles. The wave-particle duality is exemplified by the photoelectric effect, where light behaves as discrete packets of energy and mass, releasing electrons from a metal surface when the frequency is high enough. The paragraph also discusses Planck's constant and its role in quantifying the energy of electromagnetic waves, which is directly proportional to the frequency of the wave and a multiple of a constant, indicating the quantized nature of energy.

Keywords

💡Electromagnetic Force

The electromagnetic force is one of the four fundamental forces in nature, responsible for the interaction between electrically charged particles. In the context of the video, it's crucial for understanding how electricity can induce magnetism and vice versa, setting the stage for the discussion on electromagnetic radiation.

💡Electromagnetic Radiation

Electromagnetic radiation refers to the waves of the electromagnetic field that propagate through space, carrying energy. The video discusses this in the context of the electromagnetic spectrum, showing how different types of waves, from radio to gamma rays, are all forms of electromagnetic radiation.

💡Electromagnetic Spectrum

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The video describes it as being organized by wavelength and frequency, with visible light, infrared, microwaves, and radio waves at one end, and ultraviolet, X-rays, and gamma rays at the other.

💡Wavelength

Wavelength is the distance between two successive peaks of a wave. In the video, it is used to differentiate between types of electromagnetic waves, with longer wavelengths corresponding to lower frequencies and shorter wavelengths to higher frequencies.

💡Frequency

Frequency refers to the number of wave cycles passing a point per second and is inversely proportional to wavelength. The video explains that as you move up the electromagnetic spectrum, frequency decreases and wavelength increases.

💡Visible Light

Visible light is the small portion of the electromagnetic spectrum that is detectable by the human eye, ranging from violet at around 400 nanometers to red at approximately 700 nanometers. The video emphasizes that our eyes have adapted to perceive this specific range of electromagnetic radiation.

💡Infrared

Infrared radiation lies just beyond the red end of the visible light spectrum and is characterized by wavelengths in the micrometer range. The video mentions infrared as part of the electromagnetic spectrum, indicating that it has longer wavelengths and lower frequencies than visible light.

💡Ionizing Radiation

Ionizing radiation refers to radiation with enough energy to ionize atoms or molecules by knocking out electrons. The video explains that X-rays and gamma rays have high enough frequencies and energies to cause ionization, which is a key concept in understanding their effects on matter.

💡Amplitude

Amplitude is a measure of the intensity of a wave, often represented by the height of the wave's peak. In the video, amplitude is mentioned in relation to the intensity of electromagnetic radiation, with the amplitude being proportional to the number of photons present.

💡Transverse Wave

A transverse wave is a type of wave where the displacement of the medium is perpendicular to the direction of the wave's energy transfer. The video describes electromagnetic waves as transverse, with the electric and magnetic fields oscillating up and down as the wave moves forward.

💡Wave-Particle Duality

Wave-particle duality is the concept that every particle or quantum entity can be described as either a particle or a wave, depending on the situation. The video explains this by discussing the photoelectric effect, where light behaves as both a wave and as a stream of particles, or photons.

💡Photoelectric Effect

The photoelectric effect is a phenomenon in which electrons are emitted from a material (usually a metal) when it is exposed to light. The video uses this effect to illustrate the particle nature of light, as increasing the frequency of light can release electrons regardless of the light's intensity.

💡Planck's Constant

Planck's constant is a fundamental physical constant that relates the energy of a photon to its frequency. The video mentions it in the context of calculating the energy of electromagnetic waves, emphasizing that energy is quantized and proportional to frequency times Planck's constant.

Highlights

The movement of currents or electricity can induce magnetism, and the movement of magnetism can induce current.

Introduction to electromagnetic radiation and the electromagnetic spectrum in the context of an X-ray Physics course.

The electromagnetic spectrum can be oriented vertically to understand the relationship between wavelength and frequency.

Wavelength and frequency are inversely proportional; as one increases, the other decreases.

Visible light is in the middle of the electromagnetic spectrum, with wavelengths ranging from 700 to 400 nanometers.

Infrared, microwaves, and radio waves are categories of electromagnetic waves with longer wavelengths beyond red light.

Ultraviolet light, X-rays, and gamma rays are categories with shorter wavelengths and higher frequencies below violet light.

X-rays and gamma rays have high enough frequencies and energies to ionize atoms, releasing electrons.

The construction of an electromagnetic wave includes wavelength, frequency, and amplitude.

Electromagnetic waves are self-propagating and travel at the speed of light in a vacuum.

Electromagnetic waves are transverse waves, moving perpendicular to the direction of wave energy.

Electromagnetic radiation consists of two orthogonal transverse waves, demonstrating the electromagnetic force in action.

Electromagnetic radiation exhibits wave-particle duality, acting as both a wave and a particle.

The photoelectric effect demonstrates the particle nature of electromagnetic waves, releasing electrons from metal.

The energy of an electromagnetic wave is proportional to its frequency and quantized, represented by Planck's constant.

A question bank of X-ray physics related questions is available for those interested in further study.

The importance of understanding electromagnetic radiation in the study of X-ray physics.

Transcripts

in the previous talk we looked at the

electromagnetic force and how the

movement of currents or the flow of

electricity could induce magnetism and

how the movement of magnetism could

induce current and that leads us nicely

to looking at electromagnetic radiation

and the electromagnetic spectrum as we

segue now into our x-ray Physics course

proper so the electromagnetic spectrum

can be drawn in many different ways and

I like to orientate it vertically like

this I find it much easier to understand

now you'll see our electromagnetic

radiation or our electromagnetic wave

through the center of this diagram now

as we head up on this diagram we see the

wavelength the distance between

successive peaks in the wave increases

as we head up not only does the

wavelength increase as we head up but

our frequency or the number of cycles of

waves per second decreases as we head at

this diagram

as we had lowered down in the diagram

our frequency increases the number of

waves passing through a particular point

over a period of time increases and our

wavelength decreases we can see they're

inversely proportional to one another

now the wave itself is exactly the same

the structure of the wave is the same

only the wavelength and frequency is

changing here now we can divide this

spectrum into multiple different

categories depending on the wavelength

of these waves you'll see in the middle

of this spectrum is visible light

running from about 700 nanometers to

just below 400 nanometers we've got

Violet extending all the way up to Red

here now this is the most common

electromagnetic frequency within our

universe and our eyes have adapted to

see this electromagnetic radiation and

what we call Visible lines now luckily

above the red part of the spectrum we've

named that infrared these wavelengths

are in the region of micrometers as that

wavelength gets longer into the region

of centimeters we call those microwaves

and as it gets longer into the region of

meters we call those radio waves if we

go below the Violet part of the spectrum

We Now call that ultraviolet light not

visible light to our eyes the frequency

has increased our wavelength has

decreased as we then increase our

frequency further we then classify those

waves as X-rays and as that wavelength

gets slightly shorter we call that gamma

rays now as we're going to look at as

frequency increases the energy of that

wave increased and in our previous talk

we were looking at binding energy of an

electron within an atom and binding

energy was the energy required to

release that electron from an atom and

the release of an electron from an atom

is what's known as ionization we've

ionized that atom and it turns out that

X-rays and gamma rays their frequencies

are high enough their energies are high

enough to release electrons from atoms

and we call this ionizing radiation

visible light and up does not have

enough energy to ionize atoms

so let's have a look at the construction

of an electromagnetic wave and get a

couple of definitions out the way first

we can see this wave is traveling along

our x-axis here through space and we can

see the wave is perpendicular to the

direction of its flow now the distance

between successive peaks in the wave is

what's known as the wavelength we

generally measure that in meters our

wavelength the number of waves that pass

a particular point over a period of time

is known as the frequency of the wave

and our amplitude of the wave here

represents the intensity of that wave

and generally when we're talking about

electromagnetic radiation the amplitude

is proportional to the number of photons

in that electromagnetic radiation

now as I've said radio waves microwaves

X-rays and gamma rays the wave itself

the construction of the wave is exactly

the same the only thing that changes is

the wavelength and the frequency

now electromagnetic waves are

self-propagating waves as I'm going to

show you now and they travel through a

vacuum at a constant speed and that's

the speed of light it doesn't require a

medium to propagate itself propagates so

this light can travel in a vacuum so

radio waves and x-rays travel at the

same speed and our velocity here is

exactly the same for all electromagnetic

radiation going through a vacuum this is

the speed of light so if our velocity is

staying the same our frequency and our

wavelength need to be inversely

proportional as our frequency increases

our wavelength needs to decrease in

order to keep our velocity the same

now electromagnetic waves are what is

known as transverse wave that's because

the movement of energy or the direction

of the wave is perpendicular to the

movement of those waves and if you see

how this wave travels a long time in

space and we take a particular point in

that wave and watch what that point does

that point will go up and down like this

so let's have a look at this now we can

see that as the wave travels this point

will go up and back down perpendicular

to the movement of that wave you see how

it's going like that

now we can get longitudinal waves where

the molecules move in the same direction

as the propagation of the wave and we're

going to look at that in closer depth

when we look at our ultrasound waves but

the movement here in electromagnetic

radiation is transverse to the movement

of the wave

now in fact electromagnetic radiation is

not as simple as I've shown you there

it's in fact two transverse waves that

are orthogonal to one another they lie

at 90 degrees to one another and this is

where our Concepts from the

electromagnetic force come into play

I've shown you before that the movement

of current the movement of the electric

wave here represented in yellow induces

magnetism induces this magnetic wave

here represented in blue the movement of

magnetism induces current this is why

this is a self-propagating wave

electromagnetic radiation can travel

without the need for a medium when we

look at ultrasound we'll see that a

medium is required in order for an

ultrasound wave to propagate but because

this photon is self-propagating this

does not require a medium to travel

now electromagnetic radiation gets

further complicated not only is it two

orthogonal transverse waves but we can

actually think of electromagnetic weight

radiation as a particle it acts both as

a wave and as a particle and this is

what's known as wave particle duality

now electromagnetic waves act as waves

they diffract they interfere with one

another but there are certain set of

experiments that show these waves also

acting as particles now throughout this

x-ray module we're going to look at a

concept called the photoelectric effect

and it was actually the photoelectric

effect that showed these waves acting as

particles what scientists did was they

took a sheet of metal and they Shone

visible light on their sheet of metal

now if electromagnetic waves were to act

purely as waves we would expect as we

increase the intensity of that light we

increase the amplitude of that wave we

would think the energy would go up and

there would be enough energy to release

an electron from that metal and when

scientists did that there was no release

of electron what they noticed was when

they increase the frequency into the

range of x-rays even the smallest

intensity of X-ray would release an

electron and it showed now these waves

acting as particles as discrete packets

of energy and mass and it turns out a

world is quantitized electromagnetic

radiation can both act as a wave as well

as a particle and when we are

calculating the energy of a wave here we

can see that the energy of the wave is

proportional to the waves frequency as

the frequency of that wave increases so

does the energy but you can see that the

amplitude of the wave is not included in

this equation it doesn't matter the

intensity of the light the number of

photons of light doesn't increase the

wave's inherent energy

you may notice here that we are also

multiplying by this letter H and this is

known as Planck's constant so you can

see that energy is not only proportional

to frequency but it's also a multiple of

a constant and the fact that it's a

multiple of a constant speaks to the way

that energy is also quantitized so

electromagnetic radiation can act both

as a wave and as a particle and this is

known as wave particle duality

so it's really important to understand

the electromagnetic radiation especially

when looking at x-ray physics after all

x-rays are electromagnetic radiation so

this is a good place to start our x-ray

physics module and if you want to get

access to a question Bank of X-ray

physics related questions that have come

up in past papers see the first line of

the description below I've curated a

bunch of X-ray physics questions for you

that have come up in multiple different

exams over the last 10 years so check it

out if you want otherwise I'll see you

for our overview of X-ray physics in the

next talk goodbye