Energy and Waves

Nuclear heat light

The light is so important to us, it’s a matter of life or death. So, we will spend some time exploring this

concept of light energy.

Energy transfer from the Sun to Earth

a. Energy carried by electromagnetic waves

b. A vibration of energy

c. Light from the sun comes to us in the form

of a wave

d. Its energy is measured in wavelengths

So..

2. What is a wave?

a. A vibration through space and time

b. It carries energy

1. What is light?

Light Travels on Electromagnetic Waves

• Electromagnetic (EM) waves are non-mechanical waves because they don’t require a medium (substance) to travel through (that’s why they can travel through space).

• Sound waves, on the other hand, are mechanical waves because they need a substance to travel through and deliver those waves to our ears. Another example are waves that travel through water.

Parts of a Wave(don’t draw this in the box on your notes)

Wavelength (w) w = the distance from one crest to the next

(draw this in the box)

AmplitudeThe amplitude is the vertical change in the wave from its resting position (zero) to the crest or trough.

Resting position (zero)

Frequency (ƒ)• Frequency is the number of cycles per second

ƒ= # of cyclessecond

Which one has the shortest wavelength?Which one has the lowest frequency?

Relationship Between Energy, Wavelength and Frequency

Calculating wavelength and frequency

• All electromagnetic radiation travels through space (no medium) at the speed of light.

• Speed of light(c) = 300,000,000 meters per second…

OR

C = 300,000,000m/s

Relationship between speed of light, wavelength and frequency

Since speed of light (c) = frequency(f) x wavelength (λ), then you can solve for these two variables using this

formula:

c = fλ

• Units of measurement:– Frequency: Hertz (Hz)– Wavelength: meters (m)– Speed (m/s)

Speed of light

frequency

wavelength

Sample Calculation

• What is the frequency of a radio wave that has a wavelength of 375 meters?

c = fw

300,000,000 m/s = f x 375 m

300,000,000 m/s = f

375 m

800,000 Hz = f

Another Example Problem:1. A blue light wave has a wavelength of 400nm. What is its frequency?

(remember, you already know its speed).

2. We first need to convert 400nm to meters.

1 nanometer = 1 x 10-9 meters

convert to meters: 400nm x 0.000000001 meters = 0.0000004m

now: C = f x 0.0000004m

300,000,000m/s = f x 0.0000004m

300,000,000m/s 0.0000004m

= 7.5 x 1014 Hz

Now practice solving for wavelength and frequency on

your own

Review!Light Can be a Particle or a Wave

• Light can be described as a photon - a particle of energy.

AND• Light can be described as a

wave - a movement of energy through matter or space

• Non-mechanical waves don’t require a medium (substance) to travel through. They travel through space.

• Mechanical waves need a substance to travel through such as water or air.

http://www.chemistryland.com/CHM130W/10-ModernAtom/Spectra/ModernAtom.html#

How can elements be identified?

One method for identifying an element is observing the light emitted when the element is energized (heat or electricity)

In order to understand how the emitted light identifies an element, we must understand the properties of light