Radiation: Objectives

Nature of electromagnetic (EM) radiation

How radiation transfers energy and information

EM spectrum and its properties

Blackbody radiation

How temperature is related to emitted radiation

Doppler shift

The Universe and Light

Waves

Properties of Waves

Wave-Particle Duality of Photons

Diffraction of Waves

Electromagnetic Spectrum

Electromagnetic Spectrum

Electromagnetic Radiation

A photon, which is a "piece" of light, consists of vibrating electric and magnetic fields

The electric and magnetic fields are perpendicular to each other

Velocity = speed of light = c = 3 X 10⁸ m/s

Photons have energy, but no mass!

Electricity and Magnetism

Electrical charges: like repel, opposite attract

A charged particle is surrounded by an electric field, which determines the the particle's influence on other charged particles

If a charged particle vibrates back and forth, the electric field changes. The resulting disturbance travels through space as a wave.

Electromagnetic Radiation

Opacity

Why is the Sky Blue?

Blackbody Spectrum

Spectrum= range of wavelength or frequency

Intensity spectrum= amount or strength of EM radiation over a range of frequencies

Blackbody= an idealized body that absorbs and re-emits all radiation that falls on it

Laws of Radiation

Wien's Law:

Stefan's Law:

F=sT⁴

s=5.67 x 10^-8 W/(m²·K⁴)

F is the energy per unit area per second = flux density

Energy is in units of Joules (J).

1 J=kg m²/s² 1 Watt=J/s

Luminosity=L=Energy per second

=F · area

Doppler Effect

Doppler Effect= shift in the frequency/wavelength of light due to motion of emitting object toward or away from the observer

Redshift / Blueshift

Radial and transverse motion

r

Doppler Effect

Radial and transverse motion

r

Doppler Effect