Wize High School Grade 12 Physics Textbook > Wave Nature of Light

Light Waves

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Light Waves
  
Light is a type of electromagnetic wave, or electromagnetic radiation (EMR).
Electromagnetic waves are produced through the interaction of oscillating electric and magnetic fields.
Unlike mechanical waves, electromagnetic waves do not need a medium to propagate. They can travel through a medium (clear materials like water or glass), or through a vacuum!
EMR are what is known as transverse waves

Wize Concept
The key thing to remember with transverse waves is that the direction of wave propagation (the direction of v) and the direction that the particles oscillate are perpendicular to each other.

The speed of light traveling in a vacuum is:

 c=3.00×108  m/s \boxed{ \ c = 3.00 \times 10^8 \ \ m/s \ } c=3.00×108  m/s ​

Thus, the wave equation for light in a vacuum is:
 c=λf \boxed{ \ c=\lambda f \ } c=λf ​

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There is a whole spectrum of electromagnetic radiation, for the entire range of frequencies and wavelengths that light can have:

Visible light is just a small portion of the spectrum that our eyes can see, 
from waves of wavelength 760 nm (red)\bct{760 \ nm\  (\textbf{red})}760 nm (red) to 390 nm (violet)\bcfi{390 \ nm\  (\textbf{violet})}390 nm (violet).

Wize Concept
Since the speed is constant, the wavelength and frequency are inversely proportional. This means that :
high frequency = short wavelength
low frequency  = long wavelength

Wize Tip
Higher frequencies (shorter wavelengths) give us higher energy. The oscillations get more dense, and more energy is transferred by the light wave.

Practice: Different Types of Electromagnetic Radiation   
Rank the following types of electromagnetic radiation from lowest to highest energy.

Radio Waves, Infrared Radiation, X-rays, Microwaves, Visible Light, UV Radiation

X-rays < Infrared Radiation < Microwaves < UV Radiation < Visible Light < Radio Waves

Radio Waves < Microwaves < Infrared Radiation < Visible Light  <UV Radiation < X-rays

Radio Waves < Infrared Radiation < Microwaves < Visible Light < UV Radiation < X-rays

Radio Waves < Infrared Radiation < Visible Light < Microwaves < UV Radiation < X-rays

I don't know

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Example: Electromagnetic Waves 
If the sun were to blow up right now, determine how long it would take before we saw the explosion here on Earth. Distance between the Earth and the sun is 1.496 x 1011m.

Solution:

t=dvt=\frac{d}{v}t=vd​
d= 1.496 × 1011d=\ 1.496\ \times\ 10^{11}d= 1.496 × 1011

t=1.496 × 1011 m3×108  mst=\frac{1.496\ \times\ 10^{11}\ m}{3\times10^{8\ }\ \frac{m}{s}}t=3×108  sm​1.496 × 1011 m​

t= 8.32 min⁡t=\ 8.32\ \mint= 8.32 min