Light and Sound Flashcards
(29 cards)
What is the equation linking refractive index, angle of incidence and angle of refraction?
n = sin i/sin r
What is the equation linking critical angle and refractive index?
sin c = 1/n
What are transverse waves?
most are (light, all other em), a slinky spring wiggled up and down travel forward, waves on strings, ripples on water - the vibrations are at 90 degrees to the direction energy is transferred the wave, can be reflected or refracted
What are longitudinal waves?
some are (sound, ultrasound, shock), slinky when you push the end - the vibrations are along the same direction as the wave transfers energy
What is the frequency range of human hearing?
20-20000 Hz
What do waves do?
transfer energy without transferring matter
What is the law of reflection?
angle of incidence = angle of refraction
What is the normal?
imaginary line thats perpendicular to the surface at the point of incidence
Describe an experiment to investigate the refraction of light through a glass block
draw around glass block and direct ray of light through it at an angle, trace incident and emergent rays,r move block and draw refracted ray between. draw normal and use protractor to measure i and r
Describe an experiment to investigate the refraction of light through a glass triangular prism
different wave lengths of light refract by different amounts so white light disperses in different colours as it enters the prism and the different wavelengths are refracted by different amounts - rainbow effect
Describe an experiment to investigate the reflection of light through a semi circle
incident ray is aimed at curved edge of block so it always enters at right angles, this means it doesn’t bend as it enters the block only when it leaves
mark positions of rays and block on paper and use a protractor to measure i and r for different angles of incidence
What is the angle or reflection and incident?
i - angle between incoming wave and normal
r - angle between the reflected wave and normal
How to draw a ray diagram for a reflected and refracted ray?
reflected = boundary (mirror) with normal and i on the left going into mirror and r on the right bouncing off refracted = boundary and normal w i going into normal and then r bended into normal. if the 2nd material is less dense the r is larger than i
How do you achieve r = 90?
light going from a material with a higher refractive index to a lower one speeds up and so bends away from the normal (glass to air), if you keep increasing the i, the r get closer to 90 degrees and then a critical angle which means this light is refracted along the boundary and above this you get total internal reflection - no light leaves the medium
Describe what happens when the i is above, equal or below
above - no light comes out and is all internally reflected (total internal reflection)
equal - emerging ray comes out along surface, a lot of internal reflection
below - light passes out a but a little bit is internally reflected
How do optical fibres use total internal reflection?
made of plastic or glass and consist of an internal core surrounded by cladding w a lower refractive index
the core of the fibre is so narrow that light signals passing through it always hit the core-cladding boundary at angles higher than C - so the light is always internally reflected (unless bent sharply)
How do prisms use total internal reflection?
allows us to see objects not in line of sight (i.e periscope), ray of light travels into one prism where it is totally internally reflected by 90 degrees, it then travels to another prism lower down and is totally internally reflected by 90 degrees. its now traveling parallel to its initial path at a different height
What is the angle or reflection and incident?
i - angle between incoming wave and normal
r - angle between the reflected wave and normal
How to draw a ray diagram for a reflected and refracted ray?
reflected = boundary (mirror) with normal and i on the left going into mirror and r on the right bouncing off refracted = boundary and normal w i going into normal and then r bended into normal. if the 2nd material is less dense the r is larger than i
How do you achieve r = 90?
light going from a material with a higher refractive index to a lower one speeds up and so bends away from the normal (glass to air), if you keep increasing the i, the r get closer to 90 degrees and then a critical angle which means this light is refracted along the boundary and above this you get total internal reflection - no light leaves the medium
Describe what happens when the i is above, equal or below
above - no light comes out and is all internally reflected (total internal reflection)
equal - emerging ray comes out along surface, a lot of internal reflection
below - light passes out a but a little bit is internally reflected
How do optical fibres use total internal reflection?
made of plastic or glass and consist of an internal core surrounded by cladding w a lower refractive index
the core of the fibre is so narrow that light signals passing through it always hit the core-cladding boundary at angles higher than C - so the light is always internally reflected (unless bent sharply)
How do prisms use total internal reflection?
allows us to see objects not in line of sight (i.e periscope), ray of light travels into one prism where it is totally internally reflected by 90 degrees, it then travels to another prism lower down and is totally internally reflected by 90 degrees. its now traveling parallel to its initial path at a different height
How would you find the speed of sound in air?
2 microphones, oscilloscope
detected waves at each microscope can be seen as a separate wave by starting with both microphones and slowly moving away until the waves are aligned on the display but one wavelength apart. measure the distance to find wavelength and then equation to find speed in air (frequency is whatever you set it to first)
