Waves

Before we start…

1) What are some examples of waves in nature?

2) What are some variables that can be used to measure waves?

3) Do different types of waves exist? Explain.

…

1) What are some examples of waves in nature?

ripples in a pond, a guitar string, an earthquake

2) What are some variables can we use to measure waves?

wavelength, frequency, amplitude

3) Do different types of waves exist? Explain.

mechanical waves electromagnetic waves

You have 15 minutes!

Read page 92- 95 in the textbook and fill out concept review 13, (page 49), in the workbook.

Definitions

A wave is: A disturbance that travels through a

medium or space. A wave transports energy, not matter.

A transverse wave is: A wave that propagates perpendicular to

the motion of its medium. A longitudinal wave is:

A wave that propagates parallel to the motion of its medium.

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A mechanical wave is: A wave that travels through a medium. For

example: water, air or land. Transverse and longitudinal waves are mechanical.

An electromagnetic wave is: A wave in which no medium is needed, only space. Light, radio, x-rays and gamma rays are

electromagnetic. They travel through space at a speed of 186,000

miles/second, or the speed of light.

Characteristics of Waves

All waves can be characterized by four things:

The way they propagate, or move. Their amplitude. Their wavelength. Their frequency.

Characteristic #1 - PropagationTransverse Waves

A wave that propagates perpendicular to the motion of its medium.

Usually associated with waves in the water.

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Transverse waves have certain parts: Crest – the peak of a wave. Trough – the lowest point of a wave. Equilibrium – the middle part of a wave.

Characteristic #1 - PropagationLongitudinal Waves

A wave that propagates parallel to the motion of its medium.

Usually associated with sound, (sound waves). Sound is a series of vibrations moving through the air.

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Longitudinal waves have certain parts: Region of compression – region where

the particles are closer together. Region of rarefaction – region where the

particles are further apart.

Characteristic #2Amplitude

Symbol: A Amplitude refers to the amount of

energy transmitted by a wave. The more energy emitted by a wave, the

greater the amplitude. energy, amplitude.

Definition: the maximum distance travelled by a particle in the medium compared to its position at equilibrium.

In a transverse wave, simply find the maximum distance between the crest and the equilibrium.

In a longitudinal wave, it is more difficult to determine. Amplitude depends on the density in the region of compression.

Characteristic #3Wavelength

Symbol: λ (lambda) The length of a wave is the

measurement of one complete cycle of a wave.

In a transverse wave – the wavelength is the distance between two crests.

In a longitudinal wave – the wavelength includes one cycle of compression and one of rarefaction.

Wavelength

Characteristic #4Frequency

Unit of measure: hertz, (Hz) Frequency is the number of complete

waves, or cycles, that are formed at any given point over a period of time, (see wavelength).

Number of cycles per unit of time. The unit hertz refers to the number of

cycles per second. Ie – if a the frequency is 1 Hz, then the wave completes a full cycle in one second.

Stop and Read pages 96 & 97

1. What is the difference between a mechanical wave and an electromagnetic wave?

2. Give an example of each.

3. What is the medium for:a. Water waves?b. Sound waves?c. Seismic waves?

Types of Waves

There are two types of waves: Mechanical Electromagnetic

Mechanical waves require a medium or an environment in order to travel. They cannot travel through a vacuum.

Electromagnetic waves do not need a medium – they can travel through a medium, or a vacuum.

Mechanical Waves

Examples of mediums: water, land, or air. A mechanical wave arises when there is a

localized disturbance that changes the physical state of the medium. A rock is thrown into a puddle. An instrument is played.

The changes caused by the disturbance are transmitted to nearby particles, and so on. This is how a wave propagates.

Sound waves are mechanical.

Electromagnetic Waves

Electromagnetic waves are transverse waves that move just as easily in a vacuum as they do through a medium.

This is why solar rays reach us, even though they pass through the vacuum of space and the atmosphere.

Like all waves, electromagnetic waves are carrying energy. In this case, they are carrying radiant energy, in the form of light.

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There are many kinds of electromagnetic waves, classified according to their frequency and their wavelength.

The greater the frequency, the more energy they are carrying.

All electromagnetic waves together form the electromagnetic spectrum – a way to organize these waves.

Comparison

Wave Type Medium Examples Associated with

Mechanical wave

Can only move in a medium

Seismic, sound, water

Sound

Electromagnetic wave

Can propagate in a medium or a vacuum

Radio waves, light waves, UV rays, x-rays, infrared waves, gamma waves

Light

Electromagnetic Spectrum

This is the range of all possible frequencies in electromagnetic radiation.

Read pages 98 and 99.