1. An Electromagnetic Wave
Light
An Electromagnetic Wave

2. Electromagnetic wave =
a distrubance of
the electrical and
magnetic fields
which transports energy

3. The disturbance is caused by
A photon
Photons are particles of light
Photons are packets of energy

4. See p 235
Electric field vibrates perpendicular to magnetic field

5. Photons
Emitted when an e-
drops down to a lower energy level

6. Frequency of wave created depends on
Amount of energy in photon
High energy photon =
high frequency light wave
Speed of light constant in vacuum …so….
High frequency = short λ

7. Energy of Photon determined by:
Amount of energy given off by the electron as it drops to lower energy level
Energy differences between atomic energy levels differ depending on what electron shells they are

10. e- excited by absorbing Energy (can absorb photons)

11. Transmission of Light Opaque objects = don’t transmit
only absorb or reflect
Transparent objects = transmit in
straight lines
Scattering = molecules transmit in
all directions

12. Opaque objects absorb some frequencies of light
Photon absorbed
e- jumps up energy level
Unstable atom
vibrates so much
energy is converted
To heat

13. Opaque objects reflect other wavelengths
The color reflected is the color we see
If all colors reflected we see
White, all absorbed we see black

14. Transparent objects Light passes through in straight lines
Light absorbed by electrons in 1st molecule then re-emitted on opposite side
Light re-emitted is same frequency as what was absorbed
Re-emitted light goes to next molecule ……….page 238

16. Glass transparent to all visible light
But not transparent to UV
UV is natural frequency of glass molecules
Makes them resonate, converts light
to heat

17. Scattering Absorb light and re-emit in all directions
Small molecule scatter higher frequency
N2 and O2 of air scatter violet & blue
Larger particles scatter lower frequency
Very large particles absorb light and are opaque

18. Why …..
Is the sky blue?
Are clouds white?
Are storm clouds gray?