P Sci Unit 5 Waves Chapter 17 Waves

P. Sci. Unit 5 Waves Chapter 17

Waves ØA wave is a disturbance that carries energy through matter or space.

Mechanical Waves ØMost waves must travel through matter ØThe matter through which a wave travels is called the medium.

Electromagnetic Waves ØThe one wave that does not need a medium. ØLight waves are called electromagnetic waves

ØThe terms light and light waves can refer to any type of electromagnetic wave – not just visible light

Waves & Energy ØWaves carry energy l They can do work l They move objects

Waves & Vibrations ØMost waves are caused by vibrations. ØThis vibration involves transformations of energy much like those in a swinging pendulum

As waves carry the energy, the particles in the medium move. The direction of this motion determines whether the wave is a transverse or a longitudinal (compressional) wave.

Transverse Waves ØWaves in which the motion of the particles is perpendicular to the motion of the wave.

Longitudinal Wave ØWaves that cause the particles in a medium to travel parallel to the direction of the wave motion.

ØTransverse waves – water waves, electromagnetic waves ØLongitudinal waves – sound waves, springs

Surface Waves: A combination of transverse and longitudinal Ø Occur at the boundary of two mediums (ex – water and air) Ø The particles move both perpendicular and parallel to the direction that the wave travel

Review Questions ØWhat do waves carry ØWaves that travel through a medium are called ___. ØWaves that do not need to travel through a medium are called ___.

ØParticles in a transverse wave travel ___ to the wave motion ØParticles in a longitudinal wave travel __ to the wave motion ØParticles in a surface wave travel ___ to the wave motion

Wave Properties ØAmplitude ØWavelength ØPeriod ØFrequency ØWave speed

Crest & Trough ØCrest – Highest point of a wave ØTrough – lowest point of a wave. Crest Trough

Amplitude ØThe distance a wave moves from its resting position Resting position Amplitude

Amplitude cont. ØThe larger the amplitude – the more energy is carried by the wave.

Wavelength Ø The distance from any point on one wave to a corresponding point on an adjacent wave. Ø Usually crest to crest or trough to trough Wavelength

Wavelength cont. ØThe time it takes for one full wavelength of a wave to pass a certain point is called the period. ØThe symbol for wavelength is λ (the Greek letter lambda)

Period Ø The time required for one cycle, a complete motion that returns to its starting point. Ø Any periodic motion has a frequency

Frequency Ø the number of full wavelengths that pass a point in a given time (rate). Ø The greater the number of waves per second, the higher the frequency – the more energy carried by the wave. Ø The symbol for frequency is ƒ.

Wave Speed ØHow fast a wave moves. d v= t speed = frequency x wavelength 1 distance Speed = time x distance = 1 time or v=fxλ

Symbols ØV = speed Øf = frequency unit = Hz Øλ = wavelength unit = m (meter)

Wave Speed cont. ØWave speed depends on the medium. ØIn a given medium the speed of waves is constant.

Kinetic Theory and Wave Speed ØIn a solid, molecules are close together so waves travel very quickly through solids

ØIn a liquid, molecules are farther apart but can slide past one another so waves do not travel as fast as in a solid.

ØIn a gas, molecules are very far apart so a molecule has to travel far before it hits another molecule – so waves travel slow in gases.

ØThe full range of light

Light cont. ØAll electromagnetic waves in empty space travel at the same speed. 8 ØThe speed of light is 3 x 10 m/s (or 186, 000 miles per second) ØThe speed of light is constant.

Doppler Effect ØPitch = how high or low a sound is determined by the frequency. ØIf an object making sound is moving – this changes the frequency with which your ear receives the sound. ØTherefore the pitch changes

Review 1. 2. 3. 4. What is amplitude? What is wavelength? How are frequency and period related? What is the symbol for wavelength?

5. 6. 7. 8. What is the formula for frequency? What is the formula for wave speed? What is the shortest wavelength on the electromagnetic spectrum? What is the longest?