Waves
Units:
3.1- Use the following units: degree, Hertz, metre, metre/second, second.Properties of waves:
3.2- Describe longitudinal and transverse waves in ropes, springs and water where appropriate .
Transverse waves: waves move up and down, but energy moves forward. They are waves travel in a direction perpendicular to the direction of vibration. (E.g. light and water waves)
Longitudinal waves: waves move back and forth but energy moves forward. They are waves that travel in a direction parallel to the direction of vibration (E.g. sound waves)3.3- State the meaning of amplitude, frequency, wavelength and period of a wave.
Amplitude: this is the maximum displacement from the centre position. It is the height of the crest or depth of a trough measured from the rest position. (unit is meter). The bigger the amplitude the louder the sound.
Frequency: The number of one complete wave per second. The higher the frequency the higher the pitch. (unit is hertz (Hz)).
Period: the time taken for a certain point of the wave complete an oscillation, also known as a cycle. (unit is seconds)
Wavelength: the shortest distance from a certain point on one wave to the same spot on the other wave. For example two successive crests or troughs. For a longitudinal wave it is the distance between two back to back compressions or rarefactions. (unit is meter).
3.4- Recall that waves transfer energy and information without transferring matter.
A wave transfers energy and information from one place to another without transferring matter, there is an easy ways to prove this. If you place a leaf in a bowl of water, and then drop a pebble in it the water will make rings, but the leaf will not move from where it was it would only have bobbed up and down.
3.5- Recall and use the relationship between the speed, frequency and wavelength of a wave.
3.6- Use the relationship between frequency and time period.
- a higher frequency implies that move waves are produced in one second. the (T) period will be shorter.
3.7- Use the above relationships in different contexts including sound waves and electromagnetic waves.
Q1- What is the wavelength of a sound wave of frequency 100HZ?
*Remember the speed of sound is 340 m/s
A- v=f x λ
λ=v/f λ= 340 / 100 = 3.4m
Q2- A wave has an amplitude of 3.8cm, a frequency of 50Hz and a distance from a crest to the neighboring trough of 12.8cm. Determine the period of this wave.
*Remember to get rid of all extra information you don't need!
A- f=1/T...T=1/f
T=1/50
T=0.02s
Q3-a) some ripples travel 55cm in 5s. Find their speed in cm/s.
b) The wavelength of these waves is found to be 2.2 cm. What if their Frequency?
A-a) frequency is cm/s so if you have 55cm and 5s.
55 / 5= 11cm cm/s
*Don't forget to write down the measurement! (cm/s)
b) v= f x λ
f= v/ λ
f= 11 / 2.2=5Hz
*Don't forget to use your triangle
R-red
O-orange
Y -yellow *remember the last color on the visible light spectrum is violet and right after
G-green the visible light spectrum comes ultraviolet!
B-blue
I-indigo
V-violet
3.12- Recall some of the uses of electromagnetic radiation.
-Radio waves: broadcasting and communications
-Microwaves: cooking and satellite transmissions
-infrared: heaters and night vision equipment
-Visible Light: optical fibres and photography
-Ultraviolet: fluorescent lamps
-X-rays: obs. internal structure of objects and medical applications
-Gamme rays: sterilizing food and medical equipment
3.13- Recall the detrimental effects of excessive exposure of the human body to electromagnetic waves.
-Microwaves: internal heating of body tissue.
-Infra-red: skin burns
-Ultraviolet: damage to surface cells and blindness
-Gamma rays: cancer and mutations
-light waves are transverse waves that travel in straight lines.
-They reflect off objects into our eyes making it possible for us to see.
-They refract "light bending" , but remember the light ray itself is still straight.
3.15- Recall that the angle of incidence equals the angle of reflection.
" the angle of incidence equals the angle of reflection."- this is the law of reflection
- reflection is when a wave bounces off an object.
3.16- Construct ray diagrams to illustrate the formation of a virtual image in a plane mirror.
3.17- Describe experiments to investigate the refraction of light, using rectangular blocks, semicircular clocks and triangular prisms.
Method:
1.) place the glass blocks on top of a white sheet of paper, and trace it with a pencil.
2.) place a laser flat on the table and shine it through the glass block, and trace it from both sides and connect them together as in the diagram.
3.)Draw a normal line and measure both angles.
4.) repeat several times for different incident angles.
5.) make a graph and calculate a straight line.
Method:
1.) place your semi circle block on a white sheet of paper, trace it and draw a normal line straight through the center of the block.
2.)shine the laser beam through the curved side into the center of the straight side of the block.
3.)trace the laser beam, connect them both as showed in the diagrams.
4.) calculate the critical angle
sin i / sin r=n
Method:
1.) place your triangular block on a white piece of paper.
2.) shine the laser through on side of the triangle towards the center.
3.)you will get a total internal reflection. (90 degree angle)
*if you shine a white light through the triangle it will refract the spectrum, violet refracts the most because it has the shortest wavelength.
3.18- Recall and use the relationship between refractive index, angle of incidence and angle of refraction.
n=refractive index * you use this to find out what type of subs-
i=angle of incidence tance your light has been refracted through.
r=angle of refraction
-when light hits a denser material, it refracts towards the normal line, and slows down, velocity decreases but frequency doesn't .
-a constant frequency means that the same number of light waves has to pass through in the same amount of time. So as velocity decreases the wavelength has to decrease as well to keep a constant frequency.
3.19- Describe an experiment to determine the refractive index of glass, using a glass block.
shine a ray of light through the glass block. draw 2 normal lines and trace the light beam like in the diagram. Measure the angle of incidence and the angle of refraction, then use n=sin i/ sin r to find out the refractive index.
3.20- Describe the role of total internal reflection in transmitting information along optical fibers in prisms.
when all the light is reflected inside the substance.
it takes place when:
-the rays are traveling from a dense to a less dense substance.
-the angle of incidence in the substance is greater than the critical angle.
Optical fibres are hin and flexible.outer cladding has low refractive index. light rays will go in one end and come out the other thanks to total internal reflection. Optical fibers are used for telecommunications or for medical purposes mostly.
3.21- Recall the meaning of critical angle c.
-this is the angle of incidence in the denser substance for which the angle of refraction in the less dense material is a 90 degree angle.
3.22- Recall and use the relationship between critical angle, and refractive index.
3.26- Recall that sound waves are longitudinal waves which can be reflected, refracted and diffracted.
3.27- Recall that the frequency range for human hearing is 20Hz - 20 000 Hz.
-anything above 20 000 Hz is ultrasound!!!!
3.28- Describe how to measure the speed of sound in air.
Method:
1.)seal up the end of a resonance tube.
2.) connect it to a stand & clamp and place a mic. at the open end of the tube.
3.)make a sharp noise at the open end of the tube.
4.) measure the size of your tube.
5.)once you have your results calculate the echo time.
2x(tube distance) / time= speed of sound
- a higher frequency implies that move waves are produced in one second. the (T) period will be shorter.
3.7- Use the above relationships in different contexts including sound waves and electromagnetic waves.
Q1- What is the wavelength of a sound wave of frequency 100HZ?
*Remember the speed of sound is 340 m/s
A- v=f x λ
λ=v/f λ= 340 / 100 = 3.4m
Q2- A wave has an amplitude of 3.8cm, a frequency of 50Hz and a distance from a crest to the neighboring trough of 12.8cm. Determine the period of this wave.
*Remember to get rid of all extra information you don't need!
A- f=1/T...T=1/f
T=1/50
T=0.02s
Q3-a) some ripples travel 55cm in 5s. Find their speed in cm/s.
b) The wavelength of these waves is found to be 2.2 cm. What if their Frequency?
A-a) frequency is cm/s so if you have 55cm and 5s.
55 / 5= 11cm cm/s
*Don't forget to write down the measurement! (cm/s)b) v= f x λ
f= v/ λ
f= 11 / 2.2=5Hz
*Don't forget to use your triangle
The Electromagnetic spectrum
3.10- Understand that light is part of a continuous electric magnetic spectrum which includes radio, microwave, infrared, visible, ultraviolet, x-ray, gamma ray radiations and all these waves travel at the same speed in free space.
*these are all transverse waves, that travel at the speed of light, which is 3 x 10^8 m/s!
3.11- Recall the order of the electromagnetic spectrum in decreasing wavelength and increasing frequency, including the colors of the visible spectrum.
O-orange
Y -yellow *remember the last color on the visible light spectrum is violet and right after
G-green the visible light spectrum comes ultraviolet!
B-blue
I-indigo
V-violet
3.12- Recall some of the uses of electromagnetic radiation.
-Radio waves: broadcasting and communications
-Microwaves: cooking and satellite transmissions
-infrared: heaters and night vision equipment
-Visible Light: optical fibres and photography
-Ultraviolet: fluorescent lamps
-X-rays: obs. internal structure of objects and medical applications
-Gamme rays: sterilizing food and medical equipment
3.13- Recall the detrimental effects of excessive exposure of the human body to electromagnetic waves.
-Microwaves: internal heating of body tissue.
-Infra-red: skin burns
-Ultraviolet: damage to surface cells and blindness
-Gamma rays: cancer and mutations
LIGHT & SOUND
3.14- Recall that light waves are transverse waves which can be reflected and refracted.-light waves are transverse waves that travel in straight lines.
-They reflect off objects into our eyes making it possible for us to see.
-They refract "light bending" , but remember the light ray itself is still straight.
3.15- Recall that the angle of incidence equals the angle of reflection.
" the angle of incidence equals the angle of reflection."- this is the law of reflection
- reflection is when a wave bounces off an object.
3.17- Describe experiments to investigate the refraction of light, using rectangular blocks, semicircular clocks and triangular prisms.
Method:1.) place the glass blocks on top of a white sheet of paper, and trace it with a pencil.
2.) place a laser flat on the table and shine it through the glass block, and trace it from both sides and connect them together as in the diagram.
3.)Draw a normal line and measure both angles.
4.) repeat several times for different incident angles.
5.) make a graph and calculate a straight line.
Method:
1.) place your semi circle block on a white sheet of paper, trace it and draw a normal line straight through the center of the block.
2.)shine the laser beam through the curved side into the center of the straight side of the block.3.)trace the laser beam, connect them both as showed in the diagrams.
4.) calculate the critical angle
sin i / sin r=n
Method:
1.) place your triangular block on a white piece of paper.
2.) shine the laser through on side of the triangle towards the center.
3.)you will get a total internal reflection. (90 degree angle)
*if you shine a white light through the triangle it will refract the spectrum, violet refracts the most because it has the shortest wavelength.
3.18- Recall and use the relationship between refractive index, angle of incidence and angle of refraction.
n=refractive index * you use this to find out what type of subs-
i=angle of incidence tance your light has been refracted through.
r=angle of refraction
-a constant frequency means that the same number of light waves has to pass through in the same amount of time. So as velocity decreases the wavelength has to decrease as well to keep a constant frequency.
3.19- Describe an experiment to determine the refractive index of glass, using a glass block.
3.20- Describe the role of total internal reflection in transmitting information along optical fibers in prisms.
when all the light is reflected inside the substance.
it takes place when:
-the rays are traveling from a dense to a less dense substance.
-the angle of incidence in the substance is greater than the critical angle.
Optical fibres are hin and flexible.outer cladding has low refractive index. light rays will go in one end and come out the other thanks to total internal reflection. Optical fibers are used for telecommunications or for medical purposes mostly.
3.21- Recall the meaning of critical angle c.
-this is the angle of incidence in the denser substance for which the angle of refraction in the less dense material is a 90 degree angle.
3.22- Recall and use the relationship between critical angle, and refractive index.
3.27- Recall that the frequency range for human hearing is 20Hz - 20 000 Hz.
-anything above 20 000 Hz is ultrasound!!!!
3.28- Describe how to measure the speed of sound in air.
Method:
1.)seal up the end of a resonance tube.
2.) connect it to a stand & clamp and place a mic. at the open end of the tube.
3.)make a sharp noise at the open end of the tube.
4.) measure the size of your tube.
5.)once you have your results calculate the echo time.
2x(tube distance) / time= speed of sound
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