Physical Science: Chapter 15

Physical Science: Chapter 15
Characteristics of Waves Section 2

Physical Science: Chapter 15 Characteristics of Waves
Properties of Waves Transverse Wave Medium moves at right angles to the direction of energy

Properties of Waves Transverse Waves

Properties of Waves Longitudinal (compressional) wave Medium moves in same direction as energy

Properties of Waves Longitudinal/compressional waves Amplitude is how far the medium moves “sideways.”

Properties of Waves Longitudinal/compressional waves

Energy of Waves The energy of waves is determined by two factors: 1). Wave amplitude 2). Wave frequency

Wave Energy-Transverse Waves 1. Since it takes more Work to move the medium a longer distance (W=F x d), the larger the wave amplitude the more energy.

Wave Energy-Longitudinal Waves 1. Since it takes more Work to move the medium a longer distance (W=F x d), the larger the wave amplitude the more energy.

Wave Energy 2. It takes more Power to move the medium quickly,(P=W/t)

Wave Energy- 2. Since it takes uses more Power to move the medium quickly, the higher the frequency the greater the energy.

Speed of Waves Kinetic theory explains the difference speeds of mechanical waves through different materials.

Speed of Mechanical Waves Examples: Sound through air m/s Sound through water m/s Sound through steel m/s So the speed of mechanical waves depends on the medium

Speed of Mechanical Waves In gases, atoms or molecules are far apart, so they must go through a lot of empty space before hitting another particle.

Speed of Waves Molecules in liquids are closer together so they can transfer energy to other molecules quicker than in gases.

Speed of Waves In solids, atoms or molecules are close together so they can transfer energy quickly to other atoms or molecules.

Speed of EMR Waves EMR through vacuum = 3 x 108 m/s (compared to sound in air 340m/s ) Since EMR waves do NOT need a medium, they can travel faster. So the speed of waves depends on the type of wave AND the medium.

Mini-Quiz #3 1). Draw a transverse wave and label the crest, trough, wavelength and amplitude. 2). Draw a longitudinal wave and label the compression rarefaction,

Mini-Quiz #3 3). What is the speed of light through a vacuum? 4). Do mechanical waves travel faster through gases, liquids or solids? 5). Do EMR waves travel faster through a vacuum or liquids?

Mini-Quiz #3 1). Draw a transverse wave and label the crest, trough, wavelength and amplitude.

Mini-Quiz #3 2). Draw a longitudinal wave and label compression, rarefaction, wavelength & amplitude.

Mini-Quiz #3 3). What is the speed of light through a vacuum? 3 x 108 m/s or 300,000,000m/s 4). Do mechanical waves travel faster through gases, liquids or solids? Solids 5). Do EMR waves travel faster through a vacuum or liquids? Vacuum

Periods of Waves The period of a wave is the amount of time it takes for a wave to travel a distance of one wavelength.

Periods of Waves The period of a wave is measured in seconds.

Frequency of Waves The frequency of a wave is the number of full waves going past a point per second.

Frequency of Waves The frequency of a wave is measured in (wave) cycles per second, called Hertz (Hz)

Periods and Frequency of Waves The frequency of a wave is equal to the inverse of its period. Frequency = 1 Period f = 1/t

Periods and Frequency of Waves If Frequency = 1__ Period then Period = 1___ Frequency

Speed of Waves: Calculations For ALL types of waves Speed = frequency x wavelength v = f x λ (this formula can also be used to calculate frequency & wavelength)

Speed of Waves: Calculations
1). If a sound wave has a wavelength of 1.55m and a frequency of 220Hz, how fast will the wave travel through air? 2). If a wave of red light has a wavelength of 5.0 x 10-9m what would be its frequency if it was traveling through a vacuum?(Hint: Need speed of light in a vacuum?) 3). If an ocean wave has a speed of 1.20 m/s what would be its wavelength if it has a frequency of 0.60Hz?

Speed of Waves: Calculations 1). If a sound wave has a wavelength of 1.55m and a frequency of 220Hz, how fast will the wave travel through air?

Speed of Waves: Calculations 1). If a sound wave has a wavelength of 1.55m and a frequency of 220Hz, how fast will the wave travel through air? Speed = frequency x wavelength v = f x λ v = Hz x m v = 341m/s

2). If a wave of red light has a wavelength of 5.0 x 10-9m what would be its frequency if it was traveling through a vacuum? (Q. How fast does light travel through a vacuum?)

2). If a wave of red light has a wavelength of 5.0 x10-9m what would be its frequency if it was traveling through a vacuum? Speed = frequency x wavelength v = f x λ 3.0 x 108m/s = f x x 10-9m f = 6.0 x 1016Hz

3). If an ocean wave has a speed of 1.20m/s what would be its wavelength if it has a frequency of 0.60Hz?

3). If an ocean wave has a speed of 1.20m/s what would be its wavelength if it has a frequency of 0.60Hz? Speed = frequency x wavelength v = f x λ 1.20m/s = Hz x λ λ = 2.0m

Speed of Waves: Calculations Do Practice Problems p. 519 (1-3)

Periods of Waves: Calculations 1). What would be the speed of a wave with a wavelength of 3.0m and a period of 2.0s?

Periods of Waves: Calculations 1). What would be the speed of a wave with a wavelength of 3.0m and a period of 2.0s? Speed = wavelength/period v = λ / T v = 3.0m / 2.0s = 1.5m/s

Periods of Waves: Calculations 2). What would be the period of a light wave with a wavelength of 1.0 x10-5m?

Periods of Waves: Calculations 2). What would be the period of a light wave with a wavelength of 1.0 x10-5m? Period = wavelength/ speed T =λ/v= 1.0 x10-5m/3.0 x108m/s T = 3.3 x 10-14s

Wave Properties: Frequency/Pitch The pitch of sound is determined by the frequency of sound waves AS HEARD by a person.

The Doppler Effect The apparent change in the frequency of a wave due to the motion of the either the source or the observer (or both).

The Doppler Effect If the source of waves is moving toward a person the pitch sounds like it is increasing (waves are closer together)

The Doppler Effect If the source of waves is moving away the pitch sounds like it is decreasing.

The Doppler Effect The Doppler Effect also works for EMR waves. If a star is moving closer, the light looks bluer.

The Doppler Effect In astronomy, if a star is moving away from Earth, the light looks redder. If its moving towards Earth its light looks bluer.

Mini-Quiz #4 1). If a wave has a wavelength of 0.5m and a frequency of 42Hz, what is the speed of the wave? 2). If a wave has a speed of 340m/s and a frequency of 2000Hz, how long is its wavelength?

Mini-Quiz #4 3). If a wave has a speed of 3 x108 m/s, and a wavelength of 0.01m, what is the frequency of the wave? 4). If a wave has a frequency of 60Hz, what is its period?

Mini-Quiz #4 5). What is the Doppler Effect? 6). If light is blue shifted what does that mean about the object?

Mini-Quiz #4 1). If a wave has a wavelength of 0.5m and a frequency of 42Hz, what is the wave’s speed? v = f x λ v = 42Hz x 0.5m v = 21m/s

Mini-Quiz #4 2). If a wave has a speed of 340m/s and a frequency of 2000Hz, how long is the wave? v = f x λ 340m/s = 2000Hz x λ λ = 340m/s = 0.17m 2000Hz

Mini-Quiz #4 3). If a wave has a speed of 3 x108m/s, and a wavelength of 0.01m, what is the frequency? v = f x λ 3 x 108 m/s = f x 0.01m f = 3 x 108 m/s = 3 x 1010 Hz 0.01m

Mini-Quiz #4 4). If a wave has a frequency of 60Hz,what is its period? f = 1 T T = = s 60Hz

Mini-Quiz #4 5). What is the Doppler Effect? The frequency (pitch for sounds) appears to increase as an object gets closer to the observer an decreases as the object moves away. 6). If light is blue shifted what does that mean about the object? Its moving closer.

Physical Science: Chapter 15

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