Mechanical and Electromagnetic What is a Wave? It’s a disturbance that propagates through a material/medium or through space. Waves transfer energy without transporting lots of matter. Two types: Mechanical and Electromagnetic

What is a Wave? It’s a disturbance that propagates through a material/medium or through space. In order for a mechanical wave to start, energy first has to create a disturbance in an elastic (movable) medium, like air, water, oil, etc.

BUT…no medium is needed for ELECTROMAGNETIC (EM) waves. Light, radio, x-rays, and gamma rays are some examples of EM waves.

All EM waves travel through empty space (a vacuum) at a speed of approximately 3.00 x 108 m/s or 186,000 miles/sec. This speed is known as the speed of light.

Like a Slinky Like a Jump Rope

TRANSVERSE LONGITUDINAL The displacement of the particles of the medium is perpendicular to the direction of wave propagation. LONGITUDINAL The displacement of the particles of the medium is parallel to the direction of wave propagation.

SURFACE A combination of transverse and longitudinal. Click here, here, and here to view simulations of transverse and longitudinal waves.

the maximum displacement of a particle of the medium from Amplitude the maximum displacement of a particle of the medium from the rest or equilibrium position Often labeled “A,”and measured in units of length

In sound waves, amplitude corresponds to volume or loudness.

related to the position and motion of the particles of the medium Phase related to the position and motion of the particles of the medium

the shortest distance between two points that are “in phase” Wavelength the shortest distance between two points that are “in phase” Labeled as l and measured in units of length

Frequency - the number of complete waves that pass a point per unit time denoted by f and measured in units of Hz Period - the shortest time interval during which the motion of the wave repeats itself denoted by T and measured in units of time T = 1/f & f = 1/T

If you are solving wave problems that include the word “period,” you will have to use one of the two formulas below. Two-step solution. T = 1/f OR f = 1/T

In the world of sound waves, frequency corresponds to pitch.

v = d/t = l/T = f l Velocity - the speed of the wave denoted by v and measured in units of dist/time The speed of a wave depends on the properties of the medium through which it is traveling. v = d/t = l/T = f l

Reflection the turning back of a wave when it reaches the boundary of the medium through which it is traveling

Law of Reflection the angle of incidence (relative to the “normal” line is equal to the angle of reflection

Refraction the bending of a wave as it passes at an angle from one medium into another of density (“refractive index”) For refraction to occur, the wave must change speed in the new medium.

Interference This happens when two or more waves pass through a medium at the same time. The displacements caused by each wave are added together.

results in a larger amplitude results in a smaller amplitude 2 Types of Interference Constructive results in a larger amplitude Destructive results in a smaller amplitude

Read more about interference here. Click here to view the interference pattern resulting from the superposition of two transverse waves. Click here and here to view simulations of the interference of two circular waves.

Waves in Communication Communicate: to ‘share or exchange information, news, or ideas’ Communications: ‘the means of connection between people and places’ https://www.youtube.com/watch?v=GZirBwLeUik

Waves in Communication Can be speech, text, images or any form of data Emails or teleconferencing using satellite communication, cellular phones, pagers, and so on https://www.youtube.com/watch?v=GZirBwLeUik

Waves in Communication Transmitted as voltage or current through wires, radio emissions through the air, pulses of light through optical fibers. Transmissions can be thought of as ‘electromagnetic waves in communication systems’ https://www.youtube.com/watch?v=GZirBwLeUik

Waves in Communication Radio stations broadcast on different frequency ranges. Amplitude Modulation (AM) radio broadcasts and Frequency Modulation (FM) radio broadcasts. https://www.youtube.com/watch?v=GZirBwLeUik

Waves in Communication Cell phones usually transmit signals in the 900 MHz or 1.8 GHz band “M” = 1 million “G” = 1 billion “Hz” = Hertz = cycles/second FM radio broadcasts use the 88 MHz to 108 MHz band.

Digital and Analog signals Radio waves, microwaves, infrared radiation and light are the parts of the EM spectrum used for communication. There are two types of signal used: analog and digital. https://www.youtube.com/watch?v=GZirBwLeUik

Digital and Analog Signals An analog signal is always changing according to frequency and amplitude changes in the voice or music being transmitted. A digital signal has just two values – which we can represent as 0 and 1. Binary – two numbers

Digital and analog signals

The voice, music or data is converted into 0s and 1s. The signal becomes a stream of 0 and 1 values. Added to the EM wave and transmitted. Signal is received and then decoded to recover the original signal. https://www.youtube.com/watch?v=GZirBwLeUik

In communication systems, information can be sent in a one-way or a two-way direction. Called either a simplex system or duplex system.

Simplex System Duplex System Information can only be transmitted in a one-way direction, as in television and radio broadcasting Duplex System Information can be transmitted in both directions, such as with a cell phone.

https://www.youtube.com/watch?v=GZirBwLeUik

Wireless Communication Technology No cables or wires. Info transmitted through air using EM waves The tech includes such things as smart phones, computers, laptops, Bluetooth Technology, printers, GPS, Wi-Fi, dish TV, radio…

Satellite Communication The signal is a modulated microwave beam Beam sent to satellite, which amplifies the signal and sends it back to an antenna on Earth

Infrared Communication Transmitter: photo LED Receptor: photo diode The invisible IR information signal transmitted from source to target is captured and saved there by the photoreceptor. Mobile phones, remotes, TVs, security systems, laptops etc.

How do you make a radio wave? Inside the transmitter, a pulsed electrical current, DC (one direction), is sent through a wire The creates a changing EM field around the wire. This field sends a wave outward from the wire. The wave carries a coded signal, translated by the receiver

A.M. Stands for Amplitude Modulation. Information is put into a radio wave by varying the amplitude of the current To was send 1's and 0's, could have just two different levels of amplitude that correspond to these numbers--1 being high, 0 being low            

F.M. Stands for frequency modulation. Wave amplitude is kept constant, but frequency is varied                

Other kinds of electromagnetic radiation, including radio waves, are made by natural processes such as the nuclear reactions in a star.