ELECTROMAGNETIC WAVES

ELECTROMAGNETIC WAVES

Yoh 20:29b: Berbahagialah mereka yang tidak melihat, namun percaya."​

Open Ended

Write down your understanding about electromagnetic waves!

Multiple Choice

What makes electromagnetic waves different from mechanical waves?

• no medium required

• medium needed

• light -catalyzed

• space exclusive

​ELECTROMAGNETIC RADIATION

• ​Find the similarities between pictures beside?

• ​What is the difference betw​een each pictures beside?

• ​So, what is the difference between electromagnetic waves and other waves?

​I can see?

Let's explore more about EM waves

• Electromagnetic generation explained:

​https://www.youtube.com/watch?v=FWCN_uI5ygY

​

• ​Hertz experiment:

https://www.youtube.com/watch?v=9gDFll6Ge7g

​

• ​Simulation: https://javalab.org/en/radio_wave_communication_en/

Open Ended

Based on the video above, with your own words, explain how to generate electromagnetic radiation!

​ELECTROMAGNETIC WAVES

• ​Accelerating charges produce electromagnetic waves.

• ​Electromagnetic radiation, consist of oscillating electric and magnetic fields that travel away from the accelerating charges.

Multiple Choice

A point of charge at rest, gives rise to ... only

• Electric field

• Magnetic field

• Both electric and magne

Multiple Choice

A charge moving at constant velocity gives rise to

• Electric field

• Magnetic field

• Both electric and magnetic field

Multiple Choice

Electromagnetic waves produced only by charges that

• Rest

• Moving in constant speed

• Accelerated

Speed of EM Wave in Vacuum

1. ​Unlike mechanical waves, electromagnetic waves can travel through vacuum; they do not require a material medium.

2. ​Looking back at the laws that describe electric and magnetic fields, we find two universal constants. One of them is the permittivity of free space, found in Coulomb’s law and Gauss’s law; it is associated with the electric field. The second is the permeability of free space, found in Ampère’s law; it is associated with the magnetic field

Speed of EM Wave in Vacuum

​Speed of Light in Matter

​When an EM wave passes from one medium to another, the frequency and wavelength cannot both remain unchanged since the wave speed changes and v = fλ.

As is the case with mechanical waves, it is the wavelength that changes; the frequency remains the same.

​Speed of Light in Matter

Instead of specifying the speed, it is common to specify the index of refraction n.

Index of refraction: n = c/v

Since the frequencies are equal,

Multiple Choice

A supernova is an exploding star; a supernova is billions of times brighter than an ordinary star. Most supernovae occur in distant galaxies and cannot be observed with the naked eye. The two supernovae visible to the naked eye occured in 1604 and 1987. Supernova SN1987 occures 1.6 x $$10^{21}$$  m from Earth. When did the explosion occur?

• 170000 years before

• 160000 years before

• 150000 years before

• 140000 years before

Multiple Choice

Light entering the eye passes in turn through the aqueous fluid (n=1.33), the lens (n=1.44), and the vitreous fluid (n=1.33), before reaching the retina. If light with wavelength 480 nm in air enters the eye, what is its wavelength in the vitreous fluid?

• 360 nm

• 640 nm

• 480 nm

​Dispersion

1. ​Speed of EM waves in a material medium does depend on frequency.

2. ​The index of refraction is not a constant for a given material, it is a funcion of frequency.

3. ​Variation of the speed of a wave with frequency is called dispersion.

​

​CHARACTERISTICS OF ELECTROMAGNETIC WAVE

Look at this three simulation below:

https://ophysics.com/em3.html

​

https://javalab.org/en/electromagnetic_wave_en/

​

https://javalab.org/en/radio_wave_communication_en/

Multiple Choice

Based on the picture and simulation, which one is the characteristics of electromagnetic waves?

• The electric and magnetic fields oscillate at the different frequency.

• The electric and magnetic fields oscillate in phase with one another

• The amplitudes of the electric and magnetic fields are same to one another

• Instantaneous magnitudes of the fields are nproportional at any point

Characteristics of EM Waves​

• ​EM waves in vacuum travel at speed c = 3.00 × 10⁸ m/s, independent of frequency. The speed is also independent of amplitude

• The electric and magnetic fields oscillate at the same frequency. Thus, a single frequency f and a single wavelength λ= c/f pertain to both the electric and magnetic fields of the wave. 

• The electric and magnetic fields oscillate in phase with one another. That is, at a given instant, the electric and magnetic fields are at their maximum magnitudes at a common set of points. Similarly, the fields are both zero at a common set of points at any instant.

Characteristics of EM Waves​

• The amplitudes of the electric and magnetic fields are proportional to one another. The ratio is c: Em = c Bm

• Since the fields are in phase and the amplitudes are proportional, the instantaneous magnitudes of the fields are proportional at any point.

• ​The EM wave is transverse; that is, the electric and magnetic fields are each perpendicular to the direction of propagation of the wave. 

• The fields are also perpendicular to one another. Therefore, E, B, and the velocity of propagation are three mutually perpendicular vectors.

Characteristics of EM Waves​

• At any point, E x B is always in the direction of propagation 

  The electric energy density is equal to the magnetic energy density at any point.The wave carries exactly half its energy in the electric field and half in the magneticfield.

Open Ended

Write down at least 2 characteristics of electromagnetic waves!