ELECTROMAGNETIC RADIATION

• subatomic particles (electron, photon, etc) have both PARTICLE and WAVE properties

• Light is electromagnetic radiation - crossed electric and magnetic waves:

Properties :Wavelength, l (nm)

Frequency, n (s-1, Hz)Amplitude, Aconstant speed. c

3.00 x 108 m.s-1

Electromagnetic Radiation

wavelengthVisible light

wavelengthUltaviolet radiation

Amplitude

Node

ELECTROMAGNETIC RADIATION

c = C = speed of light, a constant (3.00 x 108 m/s)

= frequency, in units of hertz (hz, sec-1)

= wavelength, in meters

Electromagnetic radiation propagates through space as a wave moving at the speed of light.

Example: Red light has l = 700 nm. Calculate the frequency, n.

= 3.00 x 10

8 m/s

7.00 x 10-7

m

= 4.29 x 1014

Hz n = cl

• Wave nature of light is shown by classical wave properties such as • interference • diffraction

Electromagnetic Radiation

Diffraction of a Wave

Wave Interference Pattern

E = h E = Energy, in units of Joules (kg·m2/s2)

h = Planck’s constant (6.626 x 10-34 J·s)

= frequency, in units of hertz (hz, sec-1)

The energy (E ) of electromagnetic radiation is directly proportional to the frequency () of the radiation.

ELECTROMAGNETIC RADIATION

Photoelectric effect demonstrates the particle nature of light.

Number of e- ejected does NOTdepend on frequency, rather it depends on light intensity.

No e- observed until lightof a certain minimum E is used.

Photoelectric EffectAlbert Einstein (1879-1955)