Light

Waves and Particle Characteristics

Parts of a Wave

= wavelength (lambda) =frequency(nu)

Wave

Wavelength (m) – Longer wavelengths have lower energy than shorter wavelengths.We say that is inversely proportional to E

1/E

Frequency (1/sec) – As the wavelength decreases, the frequency increasesWe say that is inversely proportional to

Waves

We can use the relationship c= to solve for either the wavelength or frequency, when the other is known.

C = speed of light – This is constant in a vacuum 3.00 x 108m/sec

Example #1

Calculate the wavelength of yellow light emitted by a sodium vapor lamp if the frequency of the radiation is 5.10 x 1014Hz? (Hz = 1/sec)

C = 3.00 x 108m/s = (5.10 x 1014Hz)

5.88 x 10-7m =

Example #2

What is the wavelength of radiation with a frequency of 1.50 x 1013Hz? Does it have a longer or shorter wavelength than red light?

c = 3.00 x 108m/s = (1.50 x 1013Hz)

2.00 x 10-5m = It has a longer wavelength than red light

Light

Each element has a specific Atomic Emission Spectrum – as specific frequencies of light are emitted

What causes the frequencies of light?

Light

As e- gain Energy, they move to higher energy levels, away from the nucleus

They are moving from a Ground State to an Excited State

As the e- move back down to Ground State – that Energy must be released

Light

The amount of Energy that is absorbed or released is known as a Quantum of Energy

Energy is proportional to E

hwhere h = Plank’s Constant

Light

Plank’s Constant = 6.6262 x 10-34 Jsec

J = Joule (a unit of energy)

E ( ) = h (J sec) (1/sec)E (J)

Light

The greater the jump, the greater the amount of energy that will be released

n=6 n=1 released more energy than an e- which moves from n=6 n=5

Example #3

How much energy is released by an e- dropping from n=4 n=2 if the light that is emitted has a frequency of 5.55 x 1014 1/sec?

E = hE= 6.6262 x 10-34Jsec (5.55 x 1014

1/sec)E = 3.68 x 10-19 J

Example #4

If an electron releases 4.56 x 10-19J of energy as it drops from n=5 n=2, what color of light would be observed?

Example 4 continued

Begin with E=h4.56 x 10-19J = 6.6262 x 10-34Jsec () 6.88 x 1014 1/sec =

Next use c = 3.00 x 108m/sec = (6.88 x 1014 1/sec) 4.37 x 10-7m = Blue light is observed