Analía Bellizzi – Chemistry Classes

Ronald Reagan Senior High School

# Waves Notes

## Waves Notes-2021

A wave is a disturbance that transfers energy from place to place.

TYPES OF WAVES

Mechanical Waves – They need matter (or medium) to transfer energy.

• Sound does not travel in vacuum
• A rope vibrating forms a wave
• Water waves
• Earthquakes

Electromagnetic Waves – They do not need a medium, but some can go through matter.
They can travel even through empty space.

• Light travels through empty space
• X-rays can pass through matter revealing bones in our body

Transverse Waves

The particles move perpendicular to the movement of the wave

Characteristics of Transverse Waves

• Crest or peak: the highest part of the disturbance on a wave
• Trough: the lowest part of the disturbance on a wave
• Amplitude: the “height” of the wave from the rest point (middle line).
• Wavelength: The distance from one point on a wave to the same point on the next wave (or the distance between two peaks or two throughs. The most common unit of wavelength is the nanometer.

#### 1 meter = 109 nanometer   <=====> 1 m = 109 nm

Longitudinal Waves

• Particles vibrate in the same direction of the wave
• (parallel to the wave movement)

Characteristics of a Longitudinal waves

• Compressions: Areas where the particles are close together.
• Rarefactions: Areas where the particles are far apart.
• Wavelength: is the distance between two COMPRESIONS or two RAREFACTIONS.

Light: Waves or Particles?

• Light is just one form of electromagnetic radiation, or electromagnetic waves
• Electromagnetic waves are composed by two perpendicular disturbances, one electric and another magnetic. (That’s why we call them electromagnetic)

Which waves can pass through the atmosphere?

Our Atmosphere filters some of the rays from outer space, some of them pass through the so called “atmospheric windows”

Uses of the Electromagnetic Waves:

Spectrum of the visible light.

• What is a rainbow? A rainbow is made of the visible part of the electromagnetic spectrum which has been separated into the original colors through rain droplets in the atmosphere.
• We can produce the same effect using a prism to separate the white light into their components.

Line spectra of the elements

When heating elements, this will glow with a characteristic light.

• If we separate the light emitted by these elements we will obtain only some of the colors in the rainbow.
• Each element has its unique set of colors which can help us identify them when burning

Flame test in the lab:

Line spectra of the elements: Why do we see only certain lines?

Two ways to see the line spectra

• Line spectra of the elements can be seen in two ways

Emission spectra: the element is heated and the emitted light is analyzed.

Absorption Spectra: White Light passing through the gaseous element will absorb the same colors that are observed in the emission light.

Have a look at the video below:

Dual nature of electrons

So Electrons can behave as particles and also as WAVES…

Here you have some details about WAVES we need to know:

Waves Notes: PowerPoint Presentation (PPT format)

Waves exercises:

waves of visible light can be represented as follows:

Waves Exercises: Worksheet and exercises (PDF format)

LAB : FLAME TEST (PDF)  (DUE ONE DAY AFTER THE LAB)

Links to see the line spectra of the elements:

http://student.fizika.org/~nnctc/spectra.htm

http://profmokeur.ca/chemistry/spectemien.htm