The Electromagnetic Spectrum and Light Electromagnetic Waves transverse

The Electromagnetic Spectrum and Light

Electromagnetic Waves transverse waves consisting of alternating electric and magnetic fields. u Can travel through a vacuum u Travel at the speed of light (c) u v= 3 x 108 m/s = c u Found by Michelson's experiment u Pg 535: 1 -3 u

u See p. 534 in text

Electromagnetic Radiation u EMR requires no medium to travelcan travel thru a vacuum u Speed u 300, 000 kilometers /sec u 186, 000 miles /sec u Consists of changing electric and magnetic fields

Changing electric and magnetic fields u u u Electric field is a region where particles can be pushed or pulled. u Wherever there is an electric charge there is an electric field associated w/it. u A moving electric charge is part of an electric current u An electric current is surrounded by a magnetic field A magnetic field is a region in which magnetic forces are present When electric field changes – so does the magnetic field.

EMR - Wave or Particle? u Acts like a wave sometimes – ie: Polarizing Filter

EMR - Wave or Particle? u Acts like a particle, a photon, sometimes – ie: Photoelectric Cell

Is light a Solid? u EMR travels as a wave but can behave like a stream of particles u Wave model- Young’s Experiment showed interference u Particle model- photoelectric effect is emission of electrons from light hitting metal u Photons

Intensity u Rate at which a waves energy flows through an area u Intensity decreases as distance apart increases u Think about how bright stars are

u u u William Herschel discovered infrared radiation He was a German-born astronomer. He used a prism to separate the wavelengths present in sunlight.

Eureka – Radiation Spectrum u Video

EMS waves u u Long wavelength : Low Frequency & Low Energy Short wavelength : High Frequency & High Energy

Frequency is inversely proportional to wavelength u Large Frequency, small wavelength u

Look at the size comparison of the wavelengths!!

Notice that microwaves fall into the Radio spectrum!

EMS Frequency is inversely proportional to wavelength u Large Frequency, small wavelength u Radio- TV, Radios, radar u Microwaves- Cell phones, Microwave oven, radar u Infrared Rays- Heat, night vision u Visible light- ROY G BIV u Ultraviolet light- black lights, tanning beds u X-rays- reflected by bones u Gamma Rays- kill cancer, check brain activity u

RADAR u Acronym for Radio Detection and Ranging u Short bursts of radio waves are sent out. . the doppler effect is used…the faster the car is moving toward the source, the higher the frequency of the radio waves returning.

Radio Waves u Longest wavelengths & lowest frequency of the EMS – Include AM, FM and Television frequencies u AM – Amplitude modulation: the frequency stays the same, but there is a change in the amplitude to get different sounds etc. (travel further than FM) u FM – Frequency Modulation: slight changes in frequency

Microwave & Infrared EMR u u Microwave: used in microwave ovens & cellular phones Infrared: Fast Food Heat Lamps, use as a night time surveillance tool.

Visible Light u White light is a mixture of the entire visible light spectrum

UV, Xray & Gamma rays u u u UV from the Sun helps the body produce vitamin D, too much exposure can cause skin cancer Xrays: used extensively in medicine to see “into” the body Gamma Rays: used in medicine to treat cancer or destructive radiation from nuclear explosions.

Waves and EMS wrap up u Electromagnetic spectrum is a range of wavelengths that can travel through space and a medium u Mechanical waves require a medium such as air, liquid or solid – Travel fastest in solids – In space no one can hear you scream – waves review website

Longitudinal Waves u move particles parallel to the direction the wave is moving, “pushpull” waves. – Example – sound waves in air – Wavelength is from compression to compression

Transverse Waves Cause the medium to vibrate at right angles to the direction the wave travels u Has a crest (top) and trough (bottom) u