1. Week 3- Electromagnetic waves and SPECTRUm

2. objectives Recap wave characteristics.
Learn about Electromagnetic waves and spectrum.

3. Recap - Challenge Define and describe frequency and period related?
Define and describe how velocity and wave length, and frequency are related?
A tuning fork has a frequency of 280 Hertz and the wavelength of the sound produced is 1.5 meters. Calculate the velocity of the wave.
A wave is moving toward shore with a velocity of 5.0 m/s. If its frequency is 2.5 hertz, what is its wavelength?

4. Amplitude and Energy
Amplitude – the energy carried by a wave or how high the wave is; related to the amount of energy
For compressional waves it’s the amount of compression in the wave
Example: The higher the wave, the more energy (THINK on ocean waves)

5. For transverse waves it’s the height of the wave (E α A2 )

7. ELECTROMAGNETIC WAVES
They travel as vibrations in electrical and magnetic fields.
Have some magnetic and some electrical properties to them.

8. When an electric field changes, so does the magnetic field
When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other.
RESULT-An electromagnetic wave.

9. Electromagnetic waves travel VERY FAST – around 300,000 kilometres per second (the speed of light).
At this speed they can go around the world 8 times in one second.
Speed of electromagnetic waves in vaccum:
3 * 108 m/s

10. Waves or Particles?
Electromagnetic radiation has properties of waves but also can be thought of as a stream of particles.
Example: Light
Light as a wave: Light behaves as a transverse wave which we can filter using polarized lenses.
Light as particles (photons): When directed at a substance light can knock electrons off of a substance (Photoelectric effect)

11. Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency
GAMMA RAYS
ULTRAVIOLET RAYS
RADIO WAVES
INFRARED RAYS
X-RAYS
MICROWAVES
VISIBLE LIGHT

12. The Electromagnetic Spectrum
The electromagnetic spectrum represents the range of energy from low energy, low frequency radio waves with long wavelengths up to high energy, high frequency gamma waves with small wavelengths.

14. RedOrangeYellowGreenBlueIndigoViolet
Visible light is a small portion of this spectrum. This is the only part of this energy range that our eyes can detect. What we see is a rainbow of colors.
RedOrangeYellowGreenBlueIndigoViolet
ROY G BIV

15. Frequency Ranges of Visible Light
Red light has a frequency of roughly 4.3 × 1014 Hz, and a wavelength of about 7.0 × 10­7 m (700nm). Violet light, at the other end of the visible range, has nearly double the frequency—7.5 × 1014 Hz—and (since the speed of light is the same in either case) just over half the wavelength— 4.0 × 10­7 m (400nm).

16. The radiation to which our eyes are most sensitive has a wavelength near the middle of this range, at about 5.5 x 10-7m (550 nm), in the yellow-green region of the spectrum.

17. It is no coincidence that this wavelength falls within the range of wavelengths at which the Sun emits most of its electromagnetic energy—our eyes have evolved to take greatest advantage of the available light.

18. Why does this make sense?
The product of wavelength and frequency always equals the speed of light.
C = λν
Why does this make sense?
NOTE:
c is a constant value= 3.00 x 108 m/s

19. List the known info List the unknown
PROBLEMS
Calculate the wavelength of yellow light emitted from a sodium lamp if the frequency is
5.10 x 1014 Hz (5.10 x 1014 s-1)
List the known info List the unknown
c = 3.00 x 1010 cm/s wavelength (λ) = ? cm
Frequency (v) = 5.10 x 1014 s-1
C = λv λ = c v
λ = 3.00 x 1010 cm/s = 5.88 x 10-5 cm
5.10 x 1014 s-1

20. YOUR TURN
1- What is the wavelength of radiation with a frequency of 1.50 x 1013 s-1?
2- What frequency is radiation with a wavelength of x 10-6 cm? In what region of the electromagnetic spectrum is this radiation?
3. What is the frequency of red light of wavelength nm?

21. Homework Watch and learn: https://www.youtube.com/watch?v=hXe7EVv1y0Q
Memorize Electromagnetic spectrum. (Types of waves, frequency and wavelength ranges)
Solve the problem sheets provided in the class.
In case you lost this. You can print here: