Wave behavior:

a. Reflection - the bouncing back of a wave.

1) Sound echoes

2) Light images in mirrors

3) Law of reflection

i = r

b. Refraction - the bending of a wave caused by a change in speed as the wave moves from one medium to another.

The girl sees the

boy’s foot closer to

the surface than it

actually is.

If the boy looks down at his feet, will they seem closer to him than

they really are?

No! He is looking straight down and not at an angle. There is no

refraction for him.

c. Diffraction - the bending of a wave around the edge of an object.

1) Water waves bending around islands

2) Water waves passing through a slit and spreading out

3) Diffraction depends on the size of the obstacle or opening compared to the wavelength of the wave.

Less occurs if wavelength is smaller than the object.

More occurs if wavelength is larger than the object.

4) AM radio waves are longer and can diffract around large buildings and mountains; FM can’t.

d. Interference - two or more waves overlapping to form a new wave.

1) Constructive (in phase)

Sound waves that constructively interfere are louder

2) Destructive (out of phase)

Sound waves that destructively interfere are not as loud

Standing wave - a wave pattern that occurs when two waves equal in wavelength and frequency meet from opposite directions and continuously interfere with each other.

node antinode

Resonance - the ability of an object to vibrate by absorbing energy at its natural frequency.

AM FM

Origin: AM method of audio transmission was first successfully carried out in the mid 1870s.

FM radio was developed in the United states mainly by Edwin Armstrong in the 1930s.

Modulating differences:

In AM, a radio wave known as the "carrier" or "carrier wave" is modulated in amplitude by the signal that is to be transmitted.

In FM, a radio wave known as the "carrier" or "carrier wave" is modulated in frequency by the signal that is to be transmitted.

Importance: It is used in both analog and digital communication and telemetry.

It is used in both analog and digital communication and telemetry.

AM FM

Pros and cons: AM has poorer sound quality compared to FM, but is cheaper and can be transmitted over long distances. It has a smaller bandwidth so it can have more stations available in any frequency range.

FM is less prone to interference than AM. However, FM signals are impacted by physical barriers. FM has greater sound quality due to higher bandwidth.

Stands for: AM stands for Amplitude Modulation

FM stands for Frequency Modulation

Range: AM radio ranges from 535 to 1705 kilohertz (OR) Up to 1200 Bits per second

FM radio ranges in a higher spectrum from 88 to 108 megahertz. (OR) 1200 to 2400 bits per second

AM FM

Complexity: transmitter and receiver are simple but in case of SSBSC AM carrier syncronization is needed

tranmitter and reciver are more complex as variation of modulating signal has to converted and detected from corresponding variation in frequencies.(i.e. voltage to frequency and frequency to voltage conversion has to be done) which are quite complex

Noise: AM is more susceptible to noise because noise affects amplitude, which is where information is "stored" in an AM signal.

FM is less susceptible to noise because information in an FM signal is transmitted through varying the frequency, and not the amplitude.

Sound Wave

1. Energy is transferred from particle to particle through matter.

2. How we hear

a. Outer ear collects sound.

b. Middle ear amplifies sound.

c. Inner ear converts sound.

3. Properties of sound

a. Intensity and loudness

• Intensity depends on the energy in a sound wave.

• Loudness is human perception of intensity.

• Loudness is measured on the decibel scale.

a) Threshold of hearing (0 db)

b) Threshold of pain (120 db)

b. Frequency and pitch

•High frequency means more vibrations hitting the ear.

•Pitch is how high or how low a sound seems to be.

•Healthy humans can hear from 20 Hz to 20,000 Hz

•We are most sensitive from 440 Hz to 7,000 Hz.

Ultrasonic sound has a frequency greater than 20,000 Hz.

a) Dogs (up to 35,000 Hz)

b) Bats (over 100,000 Hz)

c) Medical diagnosis 6) Infrasonic sound has a frequency below 20 Hz; they are felt rather than heard(earthquakes, heavy machinery).

c. Speed of sound

1) 332 m/s in air at 0 C.

2) Changes by 0.6 m/s for every Celsius degree from 0 C.

3) Subsonic – slower

4) Supersonic – faster than sound

5) Sonic boom- is the sound associated with the shock waves created by an object travelling through the air faster than the speed of sound.

d. The Doppler effect – the change in pitch due to a moving wave source.

1) Objects moving toward you cause a higher pitched sound.

2) Objects moving away cause sound of lower pitch.

3) Used in radar by police and meteorologists and in astronomy.

4. Musical sound

a. Noise has no pattern.

b. Music has a pattern and deliberate pitches.

c. Sound quality describes differences of sounds that have the same pitch and loudness.

d. Every instrument has its own set of overtones.

e) Beats are pulsing variations of loudness caused by interference of sounds of slightly different frequencies.