Download Chapter 17, Section 1: Nature of Electromagnetic Waves

Chapter 17, Section 1 and 2: Nature of
Electromagnetic Waves
• Key Concepts: What does an electromagnetic
wave consist of?
• What models explain the behavior of
electromagnetic waves?
• How are electromagnetic waves alike? What
waves make up the electromagnetic
spectrum?
• Key terms: electromagnetic wave,
electromagnetic radiation, polarized light,
photoelectric effect, photon
What is an electromagnetic wave?
• An electromagnetic wave is a TRANSVERSE
wave that transfers electrical and magnetic
energy.
• It consists of vibrating electric and magnetic
fields that move through space at the speed of
light.
• It is produced by charged particles. Every
charged particle has an electric field around it.
What? Electric eels? Hit me with your electric
feels?
• No, electric fields.
• When a charged particle moves, it produces an magnetic field. The field exerts
magnetic forces that can act on certain materials.
• When a particle changes its motion, its magnetic field changes. This also causes the
electric field to change. When one vibrates, so does the other. The result is an
electromagnetic wave.
Energy
• The energy that is transferred through space by electromagnetic
waves is called electromagnetic radiation.
• These do NOT require a medium (which is why we have light coming
from the sun through space).
Speed
• All electromagnetic waves travel at the same speed in a vacuum –
about 300,000 km/second.
Electromagnetic waves
• Have both particles and waves, so there are two models to illustrate
them:
• Wave model – like transverse waves on a rope
• Particle model – the wave behaves like a stream of particles. The
movement of particles allows an electric current to flow.
• Sometimes light can cause an electron to move so much that it is knocked away,
this is called the photoelectric effect.
• Photon – a packet (or particle) of light energy
Polarized light
• Light that passes through a polarizing filter and vibrates in only one
direction.
What is the electromagnetic spectrum?
• All electromagnetic waves travel at the same speed in a vacuum, but
they have different wavelengths and different frequencies.
• Remember speed = wavelength x frequency
• The electromagnetic spectrum is the complete range of
electromagnetic waves placed in order of increasing frequency.
The spectrum
• From long wavelength, low frequency to short wavelength, high frequency:
• Radio waves -> microwaves -> infrared waves -> UV rays -> x rays -> gamma rays
• Visible light falls right between infrared and UV
Radio waves
• Radio waves are the electromagnetic waves with the longest
wavelengths and lowest frequencies. These include broadcasting
waves (carry radio and television programs)
Microwaves
• Radio waves with the shortest wavelengths and highest frequencies.
• Radar: radio detection and ranging. System that uses reflected radio
waves to detect objects. Uses the Doppler effect.
Infrared waves
• Electromagnetic waves with wavelengths shorter than radio.
• Have more energy than radio
• Sometimes called heat waves
• Heat lamps use them
• Infrared cameras –
• Thermogram is an image that shows regions of different
temperatures as different colors
Visible light
• Make up only a small part of the spectrum. Shorter wavelengths and
higher frequencies than infrared.
• Appears white because it is a mixture of colors.
• Different colors refract differently, which is why prisms separate
colors.
Ultraviolet rays
• Higher frequencies than visible light, so they carry more energy.
• Can be strong enough to damage or kill living cells.
X rays
• Carry more energy than UV. Too much exposure can cause cancer.
Gamma Rays
• Shortest wavelengths and highest frequencies. Have the greatest
amount of energy and are the most penetrating of all electromagnetic
waves.
• Some radioactive substances and certain nuclear reactions produce
them.
• Some objects in space give them off.