Waves and Energy

Energy review

• Energy- the ability to do workRemember- Potential and Kinetic• Mechanical- movement• Heat- Convection, Conduction and Radiation• Chemical- like a battery• Electromagnetic- electric circuit or light• Nuclear- fission in a nucleus• Gravitational- a ball falling

Law of conservation of ENERGY

• What is it? (It’s the same as the Law of Conservation of Mass/Matter…)

What is a wave?

• Wave- a disturbance that moves energy from place to place.

• Some require a MEDIUM- which is the material a wave travels though- solid, liquid of gas. The energy of the wave cause the particles to move.

• What type of material would make a wave move SLOW? What about FAST?

Do all waves need a medium?

• Waves that require a medium are called MECHANICAL WAVES.

• Waves that DO NOT require a medium are called ELECTROMAGNETIC WAVES.

• Waves are created when a source of energy causes a medium to vibrate, or electric/magnetic fields are created by charged particles

• A vibration is a back and forth or up and down motion, also called oscillations

2 Categories of Waves

Based on HOW the move!• A wave that moves at a right angle to how the

material moves- TRANSVERSE wave• Waves that vibrate in a parallel direction-

LONGITUDINAL wave

Rest Position

• Equilibrium, natural position, place a wave would be if nothing had disturbed it, starting point

Parts of a wave

• Amplitude- the MAXIMUM position the medium can become away from its REST position (transverse)

• OR how compressed or rarefied the wave becomes

Wavelength

• Or the distance between two similar parts of a wave

• Transverse- crest-crest or trough to trough• Longitudinal- compression to compression

Frequency

• The number of times a complete wave passes a given point in one second- measured in HERTZ (unit Hz)

Math time! Speed of waves

• Speed= wavelength x frequency• Frequency (Hertz, Hz) = speed/wavelength• Wavelength= speed/frequency

• Can you draw the triangle for this equation?

Practice problems!

• A wave has a wavelength of 2 m and a frequency of 3 Hz. What is the wave’s speed?

• The speed of a wave on a rope is 50 m/s and its wavelength is 10 m. What is the wave’s frequency?

• The speed of a wave on a guitar string is 142 m/s and the frequency is 110 Hz. What is the wavelength of the wave?

Doppler Effect- vroom!

• is the change in FREQUENCY of a wave based on the observer and the source.

• Examples- sirens, trains, cars, how we measure distances of stars…

• Compared to the initial frequency (start), the received frequency (what you hear) is higher during the approach, identical at the instant of passing by, and lower after it passes.

All about Angles

• The approach of a wave to a surface- Angle of Incidence

• Angle of a wave bouncing of a surface- Angle of Reflection

More about Waves

• Reflection- The bouncing back of a wave when it can not pass through the medium

• Refraction- The bending of a wave when it enters a new medium- changes its speed

• Diffraction- The bending/ spreading of waves as they move

around a barrier or pass through an opening

Interference!• Constructive- The interference that occurs

when two waves combine to make a wave with an AMPLITUDE LARGER than either of the original 2 waves

• Destructive- (the opposite) interference that occurs when 2 waves combine and make a new wave with an AMPLITUDE SMALLER than the originals

Types of Waves

• Sound• Water• Seismic• Light

• Let’s look at them one at a time…

SOUND!!!!

• Velocity can depend on frequency and the medium it is travelling though, can travel though all mediums- ex 1200 ft/s in air

• So can if go through a vacuum?• Longitudinal • Use your EARS to sense• The denser the material, the greater the speed(shorter distance between particles in the medium)- High notes= high frequency, Low notes = low frequency

More SOUND!• Resonance- increase in amplitude of a vibration that occurs when

external vibrations match an object’s natural frequency

• Pitch- how sound is perceived as high or low

• Intensity- amount of energy carried through a unit by means of a wave

• Decibels-a unit used to compare the loudness of sounds (dB)

• Sonic boom- is a sound associated with a shock wave where the object moving is travelling faster than the speed of sound, creates an explosion like sound

Water Waves (Liquid/Currents)

• Speed can vary depending on other forces, temperature, gravity, density

• Can be Longitudinal and Transverse.• Transmitted in water or anything in a liquid form• The radius of the circles decrease and the depth

increases (long. waves)• Feel or see the force of water• Shallow water= large amplitude and slow frequency

Seismic Waves- EARTHQUAKES

• Velocity varies depending on the material• 3 kinds- P waves- Longitudinal

S waves- Transverse Surface Waves- Both

Seismic waves travel though rocks, sediment, and whatever else crosses its path and can be felt

P waves have the highest frequency (most energy, S- waves are slower, and surface waves are the slowest

Electromagnetic Waves

• Transverse waves, don’t necessarily need a medium to travel though- can travel though all materials unless they are opaque

• The denser the material, the harder it is for light to travel (particle block movement)

• You can see light, but also feel• Low frequency = red light, High frequency =

Purple/Violet light

The Electromagnetic Spectrum!

EM Waves

• They are TRANSVERSE waves without a medium. (They can travel through empty space- vacuum)

• They travel as vibrations in electrical and magnetic fields.

• Have some magnetic and some electrical properties to them.

• Speed of electromagnetic waves = 300,000,000 meters/second (Takes light 8 minutes to move from the sun to earth {150 million miles} at this speed.)

Things to know about LIGHT

Waves or Particles• Electromagnetic radiation has properties of waves

but also can be thought of as a stream of particles.• Example: Light as wave or particles (photons)• Light as a wave: Light behaves as a transverse wave

which we can filter using polarized lenses.• When directed at a substance light can knock

electrons off of a substance (Photoelectric effect)

Spectrum

• The waves have been ordered in INCREASING frequency-

Radio Waves 103 m

• A. Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.

• B. A radio picks up radio waves through an antenna and converts it to sound waves.

• Used by cell phones • C. Each radio station in an area broadcasts at a

different frequency. # on radio dial tells frequency.• D. MRI (MAGNETIC RESONACE IMAGING)

– Uses Short wave radio waves with a magnet to create an image

How a RADIO works

– AM=Amplitude modulation—waves bounce off ionosphere can pick up stations from different cities.

– (535kHz-1605kHz= vibrate at 535 to 1605 thousand times/second)

– FM=Frequency modulation—waves travel in a straight line & through the ionosphere--lose reception when you travel out of range.

– (88MHz-108MHz = vibrate at 88million to 108million times/second)

Microwaves 10-2 m

• Microwaves—have the shortest wavelengths and the highest frequency of the radio waves.– Used in microwave ovens.

• Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food.

– Used by cell phones (sometimes)– RADAR (Radio Detection and Ranging)

• Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.

Infrared 10-5 m

• Infrared= below red• Shorter wavelength and higher frequency than

microwaves.• You can feel the longest ones as warmth on your skin• Heat lamps give off infrared waves.• Warm objects give off more heat energy than cool

objects.• Thermogram—a picture that shows regions of

different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off. Therefore people give off infrared rays.

Visible .5 X 10-6 m• Shorter wavelength and higher frequency than infrared

rays.• Electromagnetic waves we can see.• Longest wavelength= red light• Shortest wavelength= violet (purple) light• When light enters a new medium it bends (refracts). Each

wavelength bends a different amount allowing white light to separate into it’s various colors ROYGBIV.

• Sonoluminescence- when a bubble is popped in a liquid (by sound) and emits light- form of cavitation

• Bioluminescence- when an organism can make and emit light

Ultraviolet 10-8 m

• Shorter wavelength and higher frequency than visible light

• Carry more energy than visible light• Used to kill bacteria. (Sterilization of equipment)• Causes your skin to produce vitamin D (good for

teeth and bones)• Used to treat jaundice ( in some new born

babies.• Too much can cause skin cancer. • Use sun block to protect against (UV rays)

X-ray 10-11 m• Shorter wavelength and higher frequency than UV-rays• Carry a great amount of energy• Can penetrate most matter.• Bones and teeth absorb x-rays. (The light part of an x-ray

image indicates a place where the x-ray was absorbed)• Used to examine for broken bones or foreign objects• Too much exposure can cause cancer

– (lead vest at dentist protects organs from unnecessary exposure)

• Used by engineers to check for tiny cracks in structures.– The rays pass through the cracks and the cracks appear dark on

film.

Gamma 10-12 m

• Shorter wavelength and higher frequency than X-rays

• Carry the greatest amount of energy and penetrate the most.

• Used in radiation treatment to kill cancer cells• Can be very harmful if not used correctly.

- What is the relationship between frequency and wavelength?

- What is meant by ‘spectrum’?- What does ROY G BIV mean?- Which color is more energetic, red or yellow?- Which type of wave travels faster, gamma or radio?- Why are microwaves more dangerous than radio

waves?- If I were in a car accident, which section of the EM

spectrum would be the most useful and WHY?