Physics - Light and Waves
Go over rest of those questions and answers.
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What is the human hearing range?
20 - 20,000 Hz
If there are 2.5 waves in 0.5 seconds, what is the frequency?
5 waves in 1 second(s). Frequency = 5Hz
At what age does a human have the best hearing range?
Age 7.
Complete the sentence. All waves _______ (inc. s____ and l____).
All waves reflect (inc. sound and light).
How is amplitude measured on a diagram?
Half the height of the wave. Often from the axis line to the top of the wave.
What does high refractive index mean?
High refractive index means low critical angle.
What is the equation that links speed, frequency and wavelength?
Speed = frequency x wavelength (m/s) (Hz) (m) V = f x λ
Complete the sentence(s). The faster an object vibrates the higher the _________ of the wave and the ______ the pitch of a sound.
The faster an object vibrates the higher the frequency of the wave and the higher the pitch of a sound.
E.G. BBC Radio Nottingham operates at 95.5MHz (95,500,000) and the waves travel at the spreed of light, 300,000,000 (3x10^8 m/s). How long are the waves?
λ = v / f = 3 * 10^8 / 95.5 * 10^6 = 300,000,000 / 95,500,000 = 3.14m
Go over symbol, units & unit symbol table (flip).
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Go over 'Homework: Questions Sheet' in exercise book and on question sheet.
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Go over 'Worksheet: Refractive index and Critical Angle' and answers in exercise book.
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Go over completing rays in and out of blocks.
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Go over how transverse vs longitudinal waves travel through the air.
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Go over topic questions on page 38 in CGP Revision Guide.
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Listen to refraction https://www.youtube.com/watch?v=FOwDgpKTqdY
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Make sure you can draw light waves going in, inside and out of blocks of glass, wood etc.
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Pages 27-38 in CGP Revision Guide cover this topic.
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Read over question packs and any sheets on the topic.
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Refraction: Enters more optically dense medium, moves towards the normal. Leaves a more optically dense medium (enters less optically dense), moves away from the normal (just like before it entered originally).
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Remember to be consistent with significant figures (/ decimal places)
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What is the method for showing Total Internal Reflection Experiment?
1. Place a semi circular block of glass on your book and draw around it. 2. Draw a normal line at the middle of the flat side. 3. Use a ray box and single slit to shine a ray of light to the normal line (ray must enter through the curved side). 4. Change the angle of the ray of light until total internal reflection occurs. 5. Then change the angle until the light is refracted along the horizontal side. 6. Mark two dots on the path of the refracted ray with a pencil. Join the dots with a ruler to show the path of the refracted ray. 7. Measure the critical angle and mark it on your diagram.
refractive index = 1.49 If the incident angle is 35° what is the refracted angle?
1.49 = Sin(i) / Sin(r) 1.49 = Sin35 / Sin(r) r = Sin⁻¹(Sin35 / 1.49) = 22.6°
How is TIR / fibre optics used in endoscopes?
Camera at end of optical fibre. Used to view inside patients.
What is wavelength?
Distance between two corresponding points of a wave.
What is TIR used in?
Fibre optics.
What is a method that proves the law of reflection?
Get a ray box, plane mirror, sheet of paper and protractor. Draw a vertical line on the piece of paper, on the middle of a horizontal line on the sheet. This horizontal line represents the normal. The vertical line is the mirror. Place a mirror on the horizontal line. Measure angle of 15,30,45 and 60 from the normal. Use a single slit in your raybox to shine a ray of light down your 15° line. Mark the position of the reflected angle (after the normal) and the incident angle (before the normal). Trace both rays onto paper. Record the reflected and incident angle with a protractor and repeat the experiment using the other angles. Use a protractor to change the incidence angles. Repeat for averages. Independent variable: angle of incidence. Dependent variable: angle of reflection. If the angle of incidence and angle of reflection are the same, the law of reflection has been obeyed and proven. Keep angle of incidence the same.
What was the method for proving virtual images distance?
Get an object, a plane mirror and a ruler / metre stick. Place the mirror in a vertical stand and draw the mirror line on a piece of paper using a ruler. Place an object on the objective side of the mirror and draw it on the diagram. Mark 2 points on the mirror line where the ray box will be shone. Shine one beam of light from the ray box, from the object onto one of the points on the mirror line (onto the mirror). Draw the incident and reflected ray. Back trace the reflected ray onto the image side, which constructs a virtual ray. It should be a dotted line. Repeat the above steps but change the independent variable which is the incident angle. Do it on the second point. The two virtual lines should cross over and this intersection is where the image is formed. Measure the distance from the virtual image to the normal and the distance from the object to the normal. If they are the same, the theory has been proven.
If i < _ then the light ray is reflected.
If i < c then the light ray is reflected.
If i = _ then the light ray is refracted along the ________.
If i = c then the light ray is refracted along the boundary.
If i > _ then total internal __________ occurs.
If i > c then total internal reflection occurs.
If the angle of incidence equals the ________ angle then the light _______ along the surface. (if i > c then TIR occurs).
If the angle of incidence equals the critical angle then the light refracts along the surface. (if i > c then TIR occurs.)
What must you do in order for TIR to occur?
In order for TIR to occur you must go from high to low refractive index.
Diagram of TIR in fibre optic cable(?) (flip)
Law of reflection still applies. Outer cladding creats lower refractive index than core.
What is an example of a transverse wave?
Light
Are sound waves longitudinal or transverse?
Longitudinal.
What is amplitude?
Maximum displacement from the equilibrium position.
What is frequency?
No. of complete oscillations per second. No. of complete waves that pass a point in a second. (Hz)
Why must the outer cladding be a lower refractive index than the core?
Outer cladding must be a lower refractive index than the core so the light doesn't refract instead of TIR occurring.
What is the equation for refractive index?
SIn(i) / Sin(r)
refractive index = 1.49 What is the critical angle?
SinC = 1 / n SinC = 1 / 1.49 Sin⁻1(1 / 1.49) c = 42.2°
What is the equation for critical angle?
SinC = 1 / n c = critical angle. n = refractive index.
What is Snell's Law?
Snell's law (also known as Snell-Descartes law and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air. http://www.physicsclassroom.com/class/refrn/Lesson-2/Snell-s-Law
In what state is sound fastest?
Solids.
What is an example of a longitudinal wave?
Sound
State two waves which are longitudinal.
Sound. P-waves (earthquakes).
What is the equation for Time Period?
T= 1/F
What is the law of reflection?
The angle of incidence = the angle of reflection.
The bigger the vibration the bigger the _________of the wave the louder the ______.
The bigger the vibration the bigger the amplitude of the wave the louder the volume.
Why is sound the fastest in solids?
The closer the particles are together and the more structured the better the sound travels.
How is wavelength measured on a diagram?
The distance from the point of one wave to another.
What is the particle displacment like in a Longitudinal wave?
The particle displacement is parallel to the wave direction.
What is the particle displacement like in a Transverse wave?
The particle displacement is perpendicular to the direction of the cause (wave?).
What kind of wave is a sound wave?
They are a longitudinal wave.
What can sound waves be?
They can be: reflected (echos, sonar) refracted (change in velocity changes the pitch) diffracted (spread out from a door)
What is time period?
Time taken for one complete wave (s).
How is TIR / fibre optics used in telecomms?
Used for data & voice. Information travels at speed of light. Undersea cables carry info around the world.
What are sound waves caused by?
Vibration.
What is the definition of a virtual image?
Virtual images are formed when the light rays bouncing off an object onto a mirror are diverging, so the light from the object appears to be coming from a completely different place. From teacher: Image through which light rays do not actually pass. (Image which cannot be projected onto a screen.) This ray diagram shows how an image is formed in a plane mirror.
State two waves which are transverse.
Water waves. EM Waves. S-waves (earthquakes).
What is Total Internal Reflection (TIR)?
When a light ray, travelling inside an optically dense medium encounters a boundary to a less dense medium, all of it will be reflected inside the dense medium if its travelling at an angle greater than the critical angle.
When ___ of the light is reflected and none is _________ then total internal reflection has occurred.
When all of the light is reflected and none is refracted then total internal reflection has occurred.
What is refraction (of light)?
When light passes from one medium (material) to another it changes speed. This is because the speed of a wave is determined by the medium through which it is passing. When light speeds up as it passes from one material to another, the angle of refraction is bigger than the angle of incidence. For example, this happens when light passes from water to air or from glass to water. http://www.bbc.co.uk/bitesize/higher/physics/radiation/refraction/revision/1/
What is diffraction?
When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is diffraction. The extent of the spreading depends on how the width of the gap compares to the wavelength of the waves. Significant diffraction only happens when the wavelength is of the same order of magnitude as the gap. For example: a gap much larger than the wavelength causes little spreading and a sharp shadow eg light through a doorway a gap similar to the wavelength causes a lot of spreading with no sharp shadow eg sound through a doorway http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway/home_energy/introduction_to_wavesrev6.shtml
Learn all these equations (flip).
f = 1 / T v = D / T v = f * λ n = Sin(i) / Sin(r) SinC = 1/ n
What is the equation for refractive index?
n = 1 / SinC
refractive index = 1.49 If the refracted angle was 20° what is the incident angle?
n = Sin(i) / Sin(r) 1.49 = Sin(i) / Sin20 Sin(i) = 1.49 x Sin20 i = Sin⁻1(Sin20 x 1.49) = 30.6°
The block is made from glass. The incident angle is 48° and the refracted angle is 30° what is the refractive index?
n = Sin(i) / Sin(r) = SIn48 / Sin30 = 1.49
