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Motivation for Today’s Session
MS-PS4 Waves and their Applications in Technologies for Information Transfer
Students who demonstrate understanding can:MS-PS4-1: Use mathematical representations to describe a simple
model for waves that includes how the amplitude of a wave is related to the energy in a wave.
MS-PS4-2: Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.
MS-PS4-3: Integrate qualitative scientific and technical information to support the claim that digitized signals are a more reliable way to encode and transmit information than analog signals.
Two strings have the same length and tension. One string has a mass per length that is 4 times that of the other string. The fundamental frequency of the more massive string will be a) larger or b) smaller than that of the less massive string.
A musician shortens the length of a string by pushing it against the fingerboard. This causes the fundamental frequency to a) increase
b) decrease c) stay the same
Radio waves – analog transmission of information
• Travel at speed of light (approximately 3 x 108 m/s)
• Natural: lightning and astronomical objects• Artificial: fixed and mobile communication
broadcasting radar and navigation systems computer networks
• Different frequencies have different propagation characteristics.
Microphone
• Converts sound waves (5 Hz – 20 kHz) into electrical impulses
• Strength of electrical impulses corresponds to sound diagram
Oscillator
• Produces AC – alternating current• Current flows in one direction and then back. • Current that switches 1 million times a
second, generates radio waves with a frequency of 1 million Hz.
AM vs. FM
Berserkerus/Wikimedia Commons
Carrier Signal – sine wave of constant frequency
Amplitude Modulation: Sounds are encoded by differences in amplitude. 500 – 1600 kHz
Frequency Modulation: Sounds are encoded by differences in frequency. 86 – 107 MHz
Receiving Radio TransmissionReceives lots of radio signals and converts to electrical current
Amplifies sine waves matching its resonance frequency
Converts current into sound wave
Extracts modulated signal from carrier frequency
Increases power (amplitude) without changing shape of signal. Modified from How
Stuff Works 2000.