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.