WAVES

What are waves? What aren't they? Give some examples.

WAVES

A wave consists of oscillations which move without carrying matter with them.

The oscillations carry energy.

A wave can be used to carry the energy itself, or it can be used to carry a signal.

Pulse

A pulse is a single wave 'bump' or a disturbance.A pulse can easily be sent down a string or spring.

A wave is made of lots of regular pulses.

A Nice Animation

http://upload.wikimedia.org/wikipedia/commons/7/74/Simple_harmonic_motion_animation.gif

Amplitude

Amplitude determines how much energy the waves have.

More amplitude = brighter light, louder sound etc.

Wavelength = = lowercase (Greek) 'lambda'.What is the relationship between v, f and ?

http://upload.wikimedia.org/wikipedia/commons/f/fa/Wave.JPG

Transverse Waves

https://encrypted-tbn0.google.com/images?q=tbn:ANd9GcTQfDMrJa4Kw3LKud7j9t21lk9914Y7F59pyY5OXJL2r0eh28wphQ

Longitudinal Waves

Longitudinal waves are the opposite of transverse waves.

The direction of propagation is the same as the direction of vibration in the medium.

https://encrypted-tbn1.google.com/images?q=tbn:ANd9GcQR5t6Oj40x-1weZmNDzDCeZA6sv_PnjFXm7ymtMoCgOtXBQ82k_Q

Example

William is swimming at a beach with waves constantly coming from the sea. He estimates that the distance between the wave crests is 6m, and two wave crests pass him every second. How fast are the waves travelling?

Example 2

David shouts across the room at Aska. He shouts with a low frequency of 5000 Hertz, and the waves travel at a speed of 340 m/s. What is the wavelength of David's voice?

Quick Review

Write a definition in your own words of:
A. Frequency
B. Wavelength
C. Wave speed
D. Amplitude
E. Crest
F. Trough

State and explain the wave equation, including explaining why it works.

A. What is the time period of a wave if two waves pass every twenty seconds?

B. What is the frequency of the wave from A?

C. Hard: what is the relationship between time period and frequency (for any wave)? Write it like a math equation, using f for frequency and T for time period. It is ok if you can't do this question :)

The speed of sound in air is about three hundred and forty metres per second.

10. What is the frequency of a sound wave with a wavelength of 6.8 meters?

11. Humans can hear approximately twenty hertz to twenty kilohertz. Calculate the minimum and maximum wavelengths humans can hear.

12. The speed of light is 300 000 000 (3 * 108) meters per second. Calculate the wavelength of red light, given that it has a frequency of 500 000 000 000 000 (5 * 1014) Hertz.

The Microwave

Calculate the wavelength of the microwaves in a microwave oven.

Maxence is swimming in a wave pool. The wave generator creates two waves each second, and they travel at a speed of three metres per second.

A. Will Maxence notice the wave crests or troughs?

B. How far apart are two crests or two troughs?

QuantitySymbolFormulaUnit

Speed/
velocityVs = f*metres per second (m/s)

f = v/Hertz (Hz)

(lambda)

Sound

Sound is a longitudinal wave.

It can travel through liquids and all gases.

An oscilloscope can convert sound waves to visible transverse waves.

Humans can hear from around 20 Hz to 20 kHz, and the range decreases with age. A phone can typically carry waves ranging from 300Hz to 3.4kHz.

Pitch and Loudness

Recall humans can hear from 20 Hz to 20 kHz.

Frequency = pitch

Amplitude = volume

http://www.sciencelearn.org.nz/Contexts/The-Noisy-Reef/Sci-Media/Images/Graphs-of-sound-waves

Frequency Ranges

Drum = 20Hz

Low note from a singer = 100Hz.

High note from singer = 1000Hz.

Whistle = 10 000 Hz.

All images from wikimedia commons.

Testing your Speakers

Use onlinetonegenerator.com to test the speaker in your computer OR smartphone (or other device).

Either wear headphones (not too loud!) or work in groups, for obvious reasons!

Testing Skype

Use a tone generator software (tonegen is free but 'expires', or use a smartphone) to test the frequency response range of skype (or your microphone).

Noise and decibels (dB)

Noise is unwanted sound.

Sound level is measured in decibels (dB).

http://impact.books.officelive.com/ProtectYourHearing.aspx

Sound and Waves Review

1. What is a wave?2. Describe the two main types of waves.3. State the wave equation, and the formula which relates them.
4. Name one property of a wave which is not part of the wave equation. How do we observe this property of sound waves.
5. How do we observe frequency of sound waves?
6. State the maximum audible range of humans.

Ripple Tank Here

Either the real one or a virtual one :)http://phet.colorado.edu/en/simulation/wave-interference

Go to phet.colorado.edu/web-pages/simulations-base.html Go to Sound and Waves. Choose Water (top left), one drip and no barrier (centre right).

Devise an experiment to calculate the speed of the waves in the water.

Aim: To measure the effect of frequency and amplitude on wave speed in water.

Prediction: As the frequency increases, the wave speed will ____________
because ___________________________________________.As the amplitude increases, the wave speed will ____________
because ___________________________________________

Speed, Frequency, Wavelength

The velocity of waves in a medium is not affected by amplitude or frequency. What happens to the wavelength as the frequency increases?

What happens to the frequency as the wavelength increases?

Hard:
What is the mathematical relationship between frequency and wavelength?

Wavefronts

A wave can be drawn as a series of lines, where each line represents a crest.

We can also draw them as a line through the middle of the wave, often called a ray.

What is the mathematical relationship between the ray and the wavefronts?

http://www.studyphysics.ca/newnotes/20/unit03_mechanicalwaves/chp141516_waves/lesson43.htm

Reflection of Waves

The region two different media meet is called a boundary.

At a boundary a wave can reflect.

http://science.jburroughs.org/mschober/waveslite/problem6solution.html

Refraction of Waves

If a wave enters a different medium, its speed will probably change.

A change in speed causes a change in direction.

Depth of water changes the speed of waves.

Image from Giancoli Physics, Sixth Edition removed.

Diffraction

As waves pass a barrier or through a gap in a barrier, they spread out.

The diffraction is generally only noticeable if the gap is not much larger than one wavelength.

http://innovativescience.blogspot.com/2011/02/diffraction.html

Textbook work

All questions on page 95.

The Electromagnetic Spectrum

http://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/EM_Spectrum_Properties_edit.svg/675px-EM_Spectrum_Properties_edit.svg.png

Electromagnetic Spectrum

Wave ApproximateFrequencyApproximate WavelengthUses

Radio waves103mMicrowaves10-2mInfra Red Waves10-5mVisible Light5 *10-7mUltraviolet Light10-8mX Rays10-10mGamma Rays10-12m

seeing things; for cell phones and for heating things which contain water; transmitting signals; photographing bones which can't be seen with visible light; remote controls; identifying genuine or forged documents, and for purification of air and water; to sterilise food and seeds, and for cancer treatment

The words

seeing things; for cell phones and for heating things which contain water; transmitting signals; photographing bones which can't be seen with visible light; remote controls; identifying genuine or forged documents, and for purification of air and water; to sterilise food and seeds, and for cancer treatment

Signals

Electromagnetic waves are used to carry signals.

A continuous variation is called an analog signal, whereas digital signals are represented as numbers. Most early communications devices used analogue, while most modern devices use digital (exceptions?).

http://news.bbc.co.uk/2/hi/technology/6142998.stm

Signals

Electromagnetic waves are used to carry signals.

A continuous variation is called an analog signal, whereas digital signals are represented as numbers. Most early communications devices used analogue, while most modern devices use digital (exceptions?).

http://news.bbc.co.uk/2/hi/technology/6142998.stm

Radio Waves

Radio waves are used to carry signals for radio, TV and mobile phones.

Either the frequency or amplitude must be changed (modulation) to carry the signal.

http://www.softwareforeducation.com/wikileki/index.php?title=FM

Frequency Bands

Different frequencies (bandwidths) are used for different applications. They must be managed(as a resource) to ensure that people don't use the same frequency in the same place.

http://en.wikipedia.org/wiki/Radio_spectrum

AM and FM

AM radio waves can diffract around hills and mountains, so are best for rural areas.

FM signals are better quality, and are generally used in urban areas.

http://scienceaid.co.uk/physics/waves/radio.html

Fibre Optics

Fibre optics are thin glass cables which carry electromagnetic radiation(IR or visible light) inside them.

They are thinner and lighter than electrical wire, and lose less signal over long distances.

http://upload.wikimedia.org/wikipedia/commons/thumb/4/49/Fibreoptic.jpg/220px-Fibreoptic.jpg

Radio Waves

Radio waves are used to carry signals for radio, TV and mobile phones.

Either the frequency or amplitude must be changed (modulation) to carry the signal.

http://www.softwareforeducation.com/wikileki/index.php?title=FM

Diffraction of AM and FM

AM radio waves can diffract around hills and mountains, so are best for rural areas.

FM signals are better quality, and are generally used in urban areas.

http://scienceaid.co.uk/physics/waves/radio.html

Frequency Bands

Different frequencies (bandwidths) are used for different applications. They must be managed(as a resource) to ensure that people don't use the same frequency in the same place.

http://en.wikipedia.org/wiki/Radio_spectrum

Absorption by the Atmosphere

http://en.wikipedia.org/wiki/File:Atmospheric_electromagnetic_opacity.svg

The Dog at the Beach

http://www.flickr.com/photos/velo4it/1746214612/

How the Dog Runs

Sea Sand

http://commons.wikimedia.org/wiki/File:Dog_retrieving_stick.jpg

http://commons.wikimedia.org/wiki/File:2009-11-19_(31)_Branch,_Ast.JPG

http://commons.wikimedia.org/wiki/File:Brittany_Spaniel_Dog.jpg

How the Dog Runs

Sea Sand

http://commons.wikimedia.org/wiki/File:Dog_retrieving_stick.jpg

http://commons.wikimedia.org/wiki/File:2009-11-19_(31)_Branch,_Ast.JPG

http://commons.wikimedia.org/wiki/File:Brittany_Spaniel_Dog.jpg

Sand

Light

Light is an electromagnetic wave, therefore: It travels at a speed of _________.

It can travel through _________.

3) As a wave, it can d______, r_______ or r________.Light can be drawn as rays, where the ray is perpendicular to the w___________.

Light (rays) must travel in s______ l_______.

The eye detects light (more later). Some things emit light (eg __________) while most things we see reflect light (eg _____________________)

http://commons.wikimedia.org/wiki/File:Gluehbirne_2_db.jpg

Reflection of Light

Most objects reflect light but scatter it in all directions. Mirrors (and other shiny surfaces) reflect light so that they produce images.

Reflected rays follow two rules:
1. The angle of incidence equals the angle of reflection.
2. The incident ray, normal and the reflected ray all lie in the same plane.

Angle of incidence

Angle of reflection

http://upload.wikimedia.org/wikipedia/commons/b/b2/Ray_optics_diagram_incidence_reflection_and_refraction.svg

i=r

Images from Plane Mirrors

Plane mirrors form images which are:1. the same size
2. the same distance from the mirror
3. laterally inverted (left and right swapped).

A great site below:

http://www.kss.sd23.bc.ca/staff/jstracha/physics_11/course_material/unit8/U08L01/pages/ray7_plane_jpg.htm

Bookwork

Page 85 and 87.

Refraction

When light enters a different medium, it changes direction, unless it enters along the normal (an angle of incidence of ______).

As light enters a more dense medium, it slows down, and bends ____________ the normal.

As light enters a less dense medium, it speeds up, and bends ____________ from the normal.

http://www.daviddarling.info/images/refraction.gif

The Brain

Recall that the part of the brain which subconsciously controls the eye 'thinks' that light always travels in straight lines.

http://www.mikecurtis.org.uk/light3.gif

Why Something Looks Bent in Water

http://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Pencil_in_a_bowl_of_water.svg/1000px-Pencil_in_a_bowl_of_water.svg.png

Refraction and Colour

High frequency light (eg violet) is bent more than low frequency light (eg red).

This is why a prism can separate white light into its different colours.

This process is known as dispersion.

http://upload.wikimedia.org/wikipedia/commons/0/06/Prism_rainbow_schema.png

Angles

The Semi-Circular Block

When light is shone towards the centre of the (semi) circle, the angle if incidence is always ________.

The Critical Angle is the angle for which the refracted ray has an angle of refraction of 90.

10A got to here just intro TIR and CA

Total Internal Reflection

When light travels from a MORE dense medium to a LESS dense medium, it bends _____ _______ the normal.

If the refracted light has an angle of refraction greater than the critical angle, the light is instead reflected. This is called total internal reflection.

Determining The Critical Angle

Determine the critical angle for perspex.

While you are using the ray boxes, also observe and draw how light refracts through a rectangular perspex block, and the convex and concave lenses.

http://www.one-school.net/Malaysia/UniversityandCollege/SPM/revisioncard/physics/light/images/criticalangle.png

http://upload.wikimedia.org/wikipedia/commons/thumb/c/c0/Total_internal_reflection_of_Chelonia_mydas_.jpg/800px-Total_internal_reflection_of_Chelonia_mydas_.jpg

Why Do Diamonds Sparkle

http://roniece.com/wp-content/uploads/2010/09/sun.gif

http://commons.wikimedia.org/wiki/File:CZ_brilliant.jpg

Questions

Page 89 & 91.

Convex Lenses

A convex lens can produce a real image.

A real image forms when light leaves an object and meets somewhere else. The object appears to be where its image is.

Images

An image can be:

enlarged, diminished or the same size

upright or inverted

real (light focusses there) or virtual (light looks like it focuses there).

Real Images

A real image can be focussed onto a screen. The object appears to be where the image is. If it is bright and clear enough, a real image can trick the eye (and person) into thinking that something is really there.

C

F

F

Ray 1: Parallel to the principle axis and through the focus.

Ray 2: Through the optical centre.

Ray 3: Through the closest focus and then parallel to the principle axis.

principle axis

http://upload.wikimedia.org/wikipedia/commons/a/af/Pencil_drawing.png

CAMERA

Film/ CCD

If the image were a very, very long way away, what would the distance from the lens to the film be?

http://commons.wikimedia.org/w/index.php?title=File:Person_Outline_2.svg&page=1

CAMERA

Film/ CCD

If the image were a very, very long way away, what would the distance from the lens to the film be?

Answer: In the animation, as the man walked closer to the camera, the lens moved towards the man in order for the image to remain focussed on the film.

CAMERA

F

At this point, the image of the man is focussed on the film.

Film/ CCD

CAMERA

F

When the man walks closer, the(larger) image forms behind the CCD.

Film/ CCD

CAMERA

F

To keep the image focussed on the CCD, the lens is moved towards the man. The image is larger, which makes sense because the object being photographed is closer.

Film/ CCD

An Excellent Site to Try Out

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=48.msg297#msg297

In this simulation it's possible to try many different locations for objects and images.