Happy New Year!
3B 28/03/06
Take note that different waves have very different values for speeds, frequencies and wavelengths. Sound in air travels at 330m/s and tend to have wavelengths measured in cm or m. Sound in water travels at more like 1500m/s. Light, and all other electromagnetic waves, travel at 300 million m/s. The wavelengths of visible light vary from 0.4 to 0.7 millionths of a m.
Echo location works by bouncing a wave off an object and listening for the echo. The time taken for the wave to reach the object and come back again can tell you how far away the object is (as long as you know how fast the wave is travelling.)
Distance travelled = Speed times time
Because the wave travels there and back again, the distance to the object is half of the distance travelled by the wave.
Read how bats use echolocation to find their prey.
We made a measurement of the speed of sound by bouncing a loud noise made from th top of school off the Tate modern building and timing how long the sound took to get there and back. We used a map to find the distance to the Tate.
Our times were not particularly accurate even though we took an average of 4 readings. Human reaction time may have effected this.
Our speed of sound came out as about 250m/s whereas the true value is more like 330m/s
HW Set of questions on the speed of sound.
3B 24/03/06
We saw videos on the basics of waves and on noise pollution and how to avoid fit.
3H 23/03/06
We looked at performing calculations based on waves.
Wavespeed = Frequency times Wavelength
You must be able to use this formula and to rearrange it to make any of the 3 quantities the subject. (this is used in algebra in maths all the time)
Take note that different waves have very different values for speeds, frequencies and wavelengths. Sound in air travels at 330m/s and tend to have wavelengths measured in cm or m. Sound in water travels at more like 1500m/s. Light, and all other electromagnetic waves, travel at 300 million m/s. The wavelengths of visible light vary from 0.4 to 0.7 millionths of a m.
Echo location works by bouncing a wave off an object and listening for the echo. The time taken for the wave to reach the object and come back again can tell you how far away the object is (as long as you know how fast the wave is travelling.)
Distance travelled = Speed times time
Because the wave travels there and back again, the distance to the object is half of the distance travelled by the wave.
Read how bats use echolocation to find their prey.
We made a measurement of the speed of sound by bouncing a loud noise made from th top of school off the Tate modern building and timing how long the sound took to get there and back. We used a map to find the distance to the Tate.
Our times were not particularly accurate even though we took an average of 4 readings. Human reaction time may have effected this.
Our speed of sound came out as about 250m/s whereas the true value is more like 330m/s
HW Set of questions on the speed of sound.
3H 21/03/06
We did a couple of questions on waves. A new formula was introduced.
Wavespeed = Frequency * Wavelength
Diffraction: Waves spread out when passing through a gap. The smaller the gap, the more spread out the waves become. If the gap is much larger than the wavelength, then diffraction less unnoticeable.
Light is very rarely seen to diffract due to its very small wavelength (between 4 and 7 10 millionths of a metre). In order for noticeable diffraction to occur the wave must pass through a gap which is similar in size to its wavelength. (Note, waves also diffract around obstacles which are similar in size to their wavelength.)
3B 21/03/06
We played various musical instruments into the oscilloscope and saw that they all produced subltely different shaped waves. This is what makes them sound different. Each instrument has a different set of overtones which leads to the subtley different sounds.
All musical instruments require a source of vibration whose frequency can be varied to play different notes. We made up some "instruments" in the lab to play.
You saw my baritone sax, even bigger ones can play lower as a longer colomn of air vibrates.....
HW Choose your favourite musical instrument and explain on one A4 side, how it makes vibrations, how you can play different notes, loudly and softly and how it is tuned. Go into more detail for commendations.....
3B 17/03/06
We did a couple of questions on waves. A new formula was introduced.
Wavespeed = Frequency * Wavelength
Diffraction: Waves spread out when passing through a gap. The smaller the gap, the more spread out the waves become. If the gap is much larger than the wavelength, then diffraction less unnoticeable.
We saw a laser diffract and did a few a questions along with a summary of the simple facts that you have to know about waves.
Above, a thin laser beam is shone into a diffraction grating, the light spreads out from each individual tiny slit and the resulting waves interfere with each other creating the pattern.
Light is very rarely seen to diffract due to its very small wavelength (between 4 and 7 10 millionths of a metre). In order for noticeable diffraction to occur the wave must pass through a gap which is similar in size to its wavelength. (Note, waves also diffract around obstacles which are similar in size to their wavelength.)
HW I need one of each major family of musical instruments in for next time....
3H 16/03/06
We played some sounds into a microphone connected to an oscilloscope. This makes it much easier to see things like amplitude and wavelength. The sound is converted into an electrical signal by the microphone and can then be represented as a transverse wave.
Important quantities that you know are:
1. Amplitude - the maximum "height" of the vibration. Easy to see in a transverse wave, not so easy in a longitudunal.
2. Wavelength - The distance from the peak of one wave, to the peak of the next. It can really be measured from any point on the wave, to the next equivalent point.
We played higher sounds into the microphone and found that the wavelength shown on the oscilloscope screen got smaller when we played a higher note. If you play a note that is one octave higher, you double the frequency of the vibrations and the wavelength is half as big.
Louder sounds showed a larger amplitude.
We played various musical instruments into the oscilloscope and saw that they all produced subltely different shaped waves. This is what makes them sound different.
All musical instruments require a source of vibration whose frequency can be varied to play different notes. We made up some "instruments" in the lab to play.
HW Choose your favourite musical instrument and explain on one A4 side, how it makes vibrations, how you can play different notes, loudly and softly and how it is tuned. Go into more detail for commendations.....
3H 13/03/06
We saw several demonstrations relating to sound.
Sound is a longitudunal wave (as above) where the vibrations in the medium take place in the same direction as the wave is travelling.
We saw how a loudspeaker vibrates in order to cause sound and the vibrations travel through the air. We saw that the loudspeaker caused a candle flame to flicker at the same frequency as the speaker cone was.
We also tested the range of frequencies that humans can hear using a signal generator and a loudspeaker. Most of you could hear sound between 20Hz and about 20kHz. I could only hear up to about 14kHz because I am old and rubbish.
Bell jar in a vacuum demonstration.
We looked at a bell ringing in a glass jar. The air was sucked out of the jar and we could no longer hear the bell. Sound requires a medium to travel, in a vacuum sound cannot propagate. Light, however, travels easily through a vacuum. This is because it is a wave of oscillating electric and magnetic fields.
Light is an electromagnetic wave. Radiowaves, microwaves, infrared waves (those that carry heat), ultraviolet light, X rays and gamma rays are all also part of the electromagnetic spectrum and can move through a vacuum. They all move at the speed of light, which is 300 million metres a second.
Books were taken in (again).
3B 13/03/06
We saw several demonstrations relating to sound.
Sound is a longitudunal wave (as above) where the vibrations in the medium take place in the same direction as the wave is travelling.
We saw how a loudspeaker vibrates in order to cause sound and the vibrations travel through the air. We saw that the loudspeaker caused a candle flame to flicker at the same frequency as the speaker cone was.
We also played some sounds into a microphone connected to an oscilloscope. This makes it much easier to see things like amplitude and wavelength. The sound is converted into an electrical signal by the microphone and can then be represented as a transverse wave.
Important quantities that you know are:
1. Amplitude - the maximum "height" of the vibration. Easy to see in a transverse wave, not so easy in a longitudunal.
2. Wavelength - The distance from the peak of one wave, to the peak of the next. It can really be measured from any point on the wave, to the next equivalent point.
We played higher sounds into the microphone and found that the wavelength shown on the oscilloscope screen got smaller when we played a higher note. If you play a note that is one octave higher, you double the frequency of the vibrations and the wavelength is half as big.
Louder sounds showed a larger amplitude.
We also tested the range of frequencies that humans can hear using a signal generator and a loudspeaker. Most of you could hear sound between 20Hz and about 20kHz. I could only hear up to about 14kHz because I am old and rubbish.
Bell jar in a vacuum demonstration.
We looked at a bell ringing in a glass jar. The air was sucked out of the jar and we could no longer hear the bell. Sound requires a medium to travel, in a vacuum sound cannot propagate. Light, however, travels easily through a vacuum. This is because it is a wave of oscillating electric and magnetic fields.
Light is an electromagnetic wave. Radiowaves, microwaves, infrared waves (those that carry heat), ultraviolet light, X rays and gamma rays are all also part of the electromagnetic spectrum and can move through a vacuum. They all move at the speed of light, which is 300 million metres a second.
HW Your write up for all today's demonstrations to be handed in on Friday!
3B 10/03/06
We went through the light test.
3H 09/03/06
RM absent (ill) You did text book questions on waves and sounds.
HW Have cover work ready to hand in for next time.
3H 07/03/06
Going through the light test.
3B 07/03/06
We sat the light test and just started on the new topic - waves.
Light is a type of wave. Waves transfer energy from one place to another without transfering matter from one place to another. The energy is transferred as vibrations in a material, called the medium
We saw 2 different types of waves produced on a slinky.
Waves come in 2 major types, transverse and longitudunal.
In transverse waves, vibrations occur which are perpendicular to the direction in which the wave is travelling. e.g. water waves, light.
Longitudunal waves have vibrations which are parallel to the direction of wave travel.
3B 03/03/06
We taked about your half term projects. Too much information was taken from websites and not referenced, and some people missed out on some details.
We then watched a couple of videos revising light.
HW Revise all that we have covered on light (since electricity) for a big old test on Tuesday.
3H 02/03/06
We sat the light test and just started on the new topic - waves.
Light is a type of wave. Waves transfer energy from one place to another without transfering matter from one place to another. The energy is transferred as vibrations in a material, called the medium
We saw 2 different types of waves produced on a slinky.
Waves come in 2 major types, transverse and longitudunal.
In transverse waves, vibrations occur which are perpendicular to the direction in which the wave is travelling. e.g. water waves, light.
Longitudunal waves have vibrations which are parallel to the direction of wave travel.
3H 28/02/06
We taked about your half term projects. Too much information was taken from websites and not referenced, and some people missed out on some details.
We then watched a couple of videos revising light.
HW Revise all that we have covered on light (since electricity) for a big old test on Thursday.
3B 28/02/06
We did an experiment to see how lenses can be used to form images.
Putting an object close to a convex lens means that it acts like a magnifying glass and forms a virtual image if you look through it.
We also tested putting an object at different distances away from the lens. Real images were then projected onto a screen. The image was either smaller than the object with the object far away (acting like a camera) or it was larger (acting like a slide projector). In both cases the image was upside down.
We looked at the correction of short and long site using lenses.
Long sighted people are unable to focus on nearby objects. A convex (converging) lens is used to correct this.
Short sighted people have a retina which is too far away from the front of the eye. A convex (diverging) lens is needed to correct their sight.
HW Complete Qs 1-7 from handout and finish the experiment write up if not done in the lesson.
3B 24/02/06
We looked through some magnifying glasses to see how things looked.
With the object you were looking at close to the lens, a magnified image is seen through the lens. It is "virtual" (not really there).
If you changed the distance of the object from the lens then the image turned upside down.
This animation shows excellently what was happening.
We then looked at some models of the eye, which uses a convex lens to form an image on the retina at the back of the eye, hence allowing you to see!
The eye and a camera both operate in the same basic way. All the rays from the same point on an object are focussed onto the same point on the film/retina by a convex lens.
The eye can focus on nearby objects (from which the light rays are spreading out more) by squashing the lens in the eye using muscles, making it stronger (having a shorter focal length).
A camera has a lens made of glass and so it can't change shape. To focus near and far objects, the lens is moved backwards and forwards instead.
HW None, projects back next time.
3H 23/02/06
We did an experiment to see how lenses can be used to form images.
Putting an object close to a convex lens means that it acts like a magnifying glass and forms a virtual image if you look through it.
We also tested putting an object at different distances away from the lens. Real images were then projected onto a screen. The image was either smaller than the object with the object far away (acting like a camera) or it was larger (acting like a slide projector). In both cases the image was upside down.
We looked at the correction of short and long site using lenses.
Long sighted people are unable to focus on nearby objects. A convex (converging) lens is used to correct this.
Short sighted people have a retina which is too far away from the front of the eye. A convex (diverging) lens is needed to correct their sight.
HW None! I'm still marking half term projects.
3H 21/02/06
We looked through some magnifying glasses to see how things looked.
With the object you were looking at close to the lens, a magnified image is seen through the lens. It is "virtual" (not really there).
If you changed the distance of the object from the lens then the image turned upside down.
This animation shows excellently what was happening.
3B 21/02/06
We did a short practical which used lenses. A convex lens converges parallel rays of light to a point. This is called the focal point of the lens, and the distance between the centre of the lens and the focal point is called the focal length.
A concave lens diverges (spreads out) parallel rays. It has a focal point which is imaginary, made by continuing the spreading out rays onwards. Diverging lenses have a negative focal length.
Poxy fire alarm got in the way.
No HW this week as I'm mini project marking.....
3H 07/02/06
We did a short practical which used lenses. A convex lens converges parallel rays of light to a point. This is called the focal point of the lens, and the distance between the centre of the lens and the focal point is called the focal length.
A concave lens diverges (spreads out) parallel rays. It has a focal point which is imaginary, made by continuing the spreading out rays onwards. Diverging lenses have a negative focal length.
HW Optical fibres/digital project as before.
3H 07/02/06
A series of practical puzzles were attempted trying to get light to do certain things using the laws of refraction and total internal reflection.
HW Big old optical fibres and digital communications mini project is HW until after half term.
3B 07/02/06
A series of practical puzzles were attempted trying to get light to do certain things using the laws of refraction and total internal reflection.
Then the homework for half term was introduced.
An analogue signal is an exact copy of a signal (such as a sound wave). A digital signal records the level of the original signal many times a second and so the information can be sent as a series of numbers.
The series of numbers is usually turned into binary code which means it is turned into base 2. The only possible numbers in base 2 are 1 or zero.
It is much easier to retain the quality of a signal if it is sent in binary code. Any interference does not usually stop the ability of the reciever to tell the difference between a 1 or 0.
HW A large mini project piece of work which muts contain the following:
1. A description of how optical fibres work, including a diagram.
2. A discussion of the advantages of using an optical fibre to send information rather than electrical signals down copper wires.
3. An explanation of the difference between analogue and digital signals, including a diagram.
4. A discussion of the advantages of sending information digitally.
3B 03/02/06
Optical fibres.
Total internal reflection (as seen in the semi circular glass block experiment) can be used to carry light down transparent cables, called optical fibres.
Light enters the cable at one end and leaves at the other. Every time it hits the internal surface of the cable, it strikes at greater than the critical angle. Therefore total internal reflection occurs and it passes on through the cable.
We saw a video on optical fibres. Light entering the cable at one end is totally internally reflected all the way to the other end, as long as it doesn't strike the internal suface at less than the critical angle.
Advantages of optical fibres over electrical wires are:
There are a couple of disadvantages: It is hard to join (splice) optical fibres together accurately. Also, the very careful manufacturing process required for optical fibres means they need high technology and expensive factories to make them.
3H 02/02/06
Only a single lesson due to the maths challenge. We talked about optical fibres and their advantages, then about sending signals digitally instead of analogue.
An analogue signal is an exact copy of a signal (such as a sound wave). A digital signal records the level of the original signal many times a second and so the information can be sent as a series of numbers.
The series of numbers is usually turned into binary code which means it is turned into base 2. The only possible numbers in base 2 are 1 or zero.
It is much easier to retain the quality of a signal if it is sent in binary code. Any interference does not usually stop the ability of the reciever to tell the difference between a 1 or 0.
HW A large mini project piece of work which muts contain the following:
1. A description of how optical fibres work, including a diagram.
2. A discussion of the advantages of using an optical fibre to send information rather than electrical signals down copper wires.
3. An explanation of the difference between analogue and digital signals, including a diagram.
4. A discussion of the advantages of sending information digitally.
3H 31/01/06
Optical fibres.
Total internal reflection (as seen in the semi circular glass block experiment) can be used to carry light down transparent cables, called optical fibres.
Light enters the cable at one end and leaves at the other. Every time it hits the internal surface of the cable, it strikes at greater than the critical angle. Therefore total internal reflection occurs and it passes on through the cable.
We saw a video on optical fibres. Light entering the cable at one end is totally internally reflected all the way to the other end, as long as it doesn't strike the internal suface at less than the critical angle.
Advantages of optical fibres over electrical wires are:
There are a couple of disadvantages: It is hard to join (splice) optical fibres together accurately. Also, the very careful manufacturing process required for optical fibres means they need high technology and expensive factories to make them.
3B 31/01/06
We did an experiment to see how the angle of a ray of light changed as it exited a glass block.
The ray doesn't bend on the way in, it is at 90 degrees to the glass surface. It turns away from the normal on the way out, as it speeds up. It obeys Snell's law in this case.
As the angle increases, the ray is refracted nearer to the glass surface and is split into a coloured spectrum and a weak reflected ray appears.
Above a certain angle, the critical angle (about 42 degrees for glass) all of the ray is reflected back. This is called total internal reflection
HW Complete the sheet on Snell's law and refraction. Remember - n stands for the refractive index of a material. c stands for the speed of light. Divide the speed of light in a vacuum by the refractive index of a material to find the speed of light in that material.
3B 27/01/06
We did an apparent depth practical. By lining up pins, we could work out the apparent position of a pin when viewed through a perspex block. This meant intersecting 2 different rays.
The refractive index of a transparent material can be found by dividing the actual depth by the apparent depth of an object viewed through it.
The refractive index is a measure of how much light is slowed down by the material.
Speed of light in a material = Speed of light in a vacuum / Refractive index
Books taken in.
3H 26/01/06
We did an experiment to see how the angle of a ray of light changed as it exited a glass block.
The ray doesn't bend on the way in, it is at 90 degrees to the glass surface. It turns away from the normal on the way out, as it speeds up. It obeys Snell's law in this case.
As the angle increases, the ray is refracted nearer to the glass surface and is split into a coloured spectrum and a weak reflected ray appears.
Above a certain angle, the critical angle (about 42 degrees for glass) all of the ray is reflected back. This is called total internal reflection
HW Complete the sheet on Snell's law and refraction. Remember - n stands for the refractive index of a material. c stands for the speed of light. Divide the speed of light in a vacuum by the refractive index of a material to find the speed of light in that material.
3H 24/01/06
We did an apparent depth practical. By lining up pins, we could work out the apparent position of a pin when viewed through a perspex block. This meant intersecting 2 different rays.
The refractive index of a transparent material can be found by dividing the actual depth by the apparent depth of an object viewed through it.
The refractive index is a measure of how much light is slowed down by the material.
Speed of light in a material = Speed of light in a vacuum / Refractive index
Books taken in.
3B 24/01/06
An experiment was carried out to see how much rays of light bent when they passed into a glass or perspex block. Rays were found to always bend towards the normal line (90 degrees from the glass surface) when they entered the block. This bending is called refraction. It happens because the light changes speed as it enters the perspex block.
There was a mathematical relationship between the angle of incidence (angle between ray on the way in and the normal) and the angle of refraction (angle between the ray inside the block that has changed direction and the normal)
This used the function sin . sin i was proportional to sin r . You will learn about sin in maths.
sin i / sin r (the gradient of the graph you plotted) gave us an idea of how much perspex bent light. This is a property of the perspex known as its refractive index, n. Our answer was about 1.4. This means that light travels 1.4 times slower in perspex than it does in air. (air hardly slows down light at all - it has a refractive index of very slightly over 1)
Your experimental work was taken to be assessed.
HW Qs 1-8 P89-91 Spectrum Physics
3B 20/01/06
Some coins had been stuck into the bottom of some metal beakers. The coins, which were slightly out of view, became visible when the metal beakers were filled with water. This could not be explained by light travelling in straight lines. The light that reflected from the coin was bent somehow when it moved from the water back out into the air. This allowed us to see "around the corner".
This phenomenon is known as refraction. It occurs because light travels at a slower speed in transparent mediums (materials that it can pass through)than it does in air/a vacuum.
This also makes objects viewed underwater appear shallower than they actually are.
Books in.
3H 19/01/06
An experiment was carried out to see how much rays of light bent when they passed into a glass or perspex block. Rays were found to always bend towards the normal line (90 degrees from the glass surface) when they entered the block. This bending is called refraction. It happens because the light changes speed as it enters the perspex block.
There was a mathematical relationship between the angle of incidence (angle between ray on the way in and the normal) and the angle of refraction (angle between the ray inside the block that has changed direction and the normal)
This used the function sin . sin i was proportional to sin r . You will learn about sin in maths.
sin i / sin r (the gradient of the graph you plotted) gave us an idea of how much perspex bent light. This is a property of the perspex known as its refractive index, n. Our answer was about 1.4. This means that light travels 1.4 times slower in perspex than it does in air. (air hardly slows down light at all - it has a refractive index of very slightly over 1)
Your experimental work was taken to be assessed.
HW Qs 1-8 P89-91 Spectrum Physics
3H 17/01/06
We remembered some fairly important facts about light. It is emitted by luminous objects and only reflected by other objects. It travels at a great speed (300 million m/s) in a straight line unless it reflects off an object.
However...
Some coins had been stuck into the bottom of some metal beakers. The coins, which were slightly out of view, became visible when the metal beakers were filled with water. This could not be explained by light travelling in straight lines. The light that reflected from the coin was bent somehow when it moved from the water back out into the air. This allowed us to see "around the corner".
This phenomenon is known as refraction. It occurs because light travels at a slower speed in transparent mediums (materials that it can pass through)than it does in air/a vacuum.
This also makes objects viewed underwater appear shallower than they actually are.
Books in.
3B 17/01/06
We sat the electricity quiz and marked it. Then the answers to the test from last time were gone through.
Then we moved on to introduce light. We recapped the idea of colours.
The primary colours are red, green and blue. Mix all three together and we see white. This is due to us having seperate red, green and blue colour sensitive cones in our retinas. When they all fire off simultaneously, we see white.
However, white light from the Sun comes with all of the the colours of the rainbow present (RedOrangeYellowGreenBlueIndigoViolet). Light can be split into its constituent parts by using a prism, this also occurs naturally in a rainbow.
Red objects appear red because they absorb all light except red, which they reflect. A red filter only allows red light ot pass through it.
You filled in a table showing what happened when a pair of filters were placed over each other.
HW Answer all the questions from the handout sheet in your book.
3H 12/01/06
We went through the test done on Tuesday. Then we sat and marked the small extra quiz as promised.
Then we moved on to introduce light. We recapped the idea of colours.
The primary colours are red, green and blue. Mix all three together and we see white. This is due to us having seperate red, green and blue colour sensitive cones in our retinas. When they all fire off simultaneously, we see white.
However, white light from the Sun comes with all of the the colours of the rainbow present (RedOrangeYellowGreenBlueIndigoViolet). Light can be split into its constituent parts by using a prism, this also occurs naturally in a rainbow.
Red objects appear red because they absorb all light except red, which they reflect. A red filter only allows red light ot pass through it.
HW Finish Qs 1-8 P93-95
3H 10/01/06
Same as 3H in all details really. Remember to revise for the little top up quiz next time too.
HW Top up quiz same as 3H below.
3B 10/01/06
We sat the promised electricity test - this covered Ohm's law and adding resistances.
HW Revise circuit symbols, diodes, thermistors and general electricity for an quiz on Friday.
