Section 3: Light and sound Flashcards
What are light waves?
Transverse waves which can be reflected, refracted and diffracted
refraction
Light waves change speed when they pass through objects of different densities, this causes them to change direction. When they return to the original density they will continue in the original direction.
reflection
Light hitting a reflective surface will ‘bounce’ back from the surface (at the same angle they hit the surface.)
diffraction
When light meats a barrier, it will carry on through the gap and spread out in the area beyond.
What is the law of reflection?
The angle of incidence is the angle that light hits a mirror; it is taken between 90 degrees from the mirror and the incidence wave (the wave that hits the mirror.)
The angle of reflection is the angle that light leaves the mirror; it is taken between 90 degrees from the mirror and the angle of reflection.
The angle of incidence is always the same as the angle of reflection.
Describe an experiment to determine the refractive index of glass using a glass block
Shine a ray of light through a glass block, measure the angle of incidence and the angle of refraction. Do sin(i) divided by sin(r) and you will have the refractive index of glass.
Describe experiments to investigate the refraction of light, using rectangular blocks, semicircular blocks and triangular prisms
Place a block of glass on a piece of paper, drawing an outline.
At one point, draw the normal line.
Draw a line at 30 degrees to the normal line, shine a ray of light down this line.
Draw a line where the light comes out the other side. Connect the two lines, drawing the refracted ray.
Measure the angle of the emergent ray.
Repeat for different shaped glass.
What is the relationship between refractive index, angle of incidence and refraction
refractive index = angle of incidence / angle of refraction
n = sin i / sin r
Describe the role of total internal reflection in transmitting information along optical fibres and in prisms
Beyond the critical angle, light will be reflected back into the medium they came from at the same angle. In this way they are trapped in the medium.
By reflecting light past its critical angle you can make it travel through a medium to send information: this is done in optical fibres
What is the critical angle?
The angle of incidence at which maximum refraction occurs
Analogue signals
The amplitude and/or frequency constantly vary.
Digital signals
Consists of pulses with two states: on; off
What is the relationship between the critical angle and refractive index?
sin c = 1 / n
sin (critical angle) = 1 / refractive index
What are the advantages of using digital signals ?
As signals get transmitted, they become weaker and need to be amplified. Regeneration of digital signals create a clean, accurate copy of the original.
However regeneration of analogue signals also amplify any accompanied noise, which may create errors in the signal.
What are sound waves?
Longitudinal waves which can be reflected, refracted and diffracted
What is the frequency range for human hearing?
20 Hz - 20 000 Hz
Describe an experiment to measure the speed of sound in air
Measure the distance between two places, have a sound made in one place, as soon as you see the sound has been made start a stop watch, as soon as you hear the sound made stop the stopwatch.
distance/time= speed
How is an oscilloscope and microphone used to display sound waves?
A microphone detects sound waves, it can feed this information into an oscilloscope which will display it as a wave (or straight line.)
Describe an experiment using an oscilloscope to determine the frequency of a wave
Have an noise made into a microphone attached to an oscilloscope, for example have someone try to sing a note. See how many oscillations there are per second, this will be your frequency. Try changing the pitch of the note and see it the number of oscillations per second changes.
An oscillation is the completion of one wave i.e from one peak and the next.
What does the pitch of sound depend on?
The frequency of vibration of the source
What des the loudness of a sound depend on?
The amplitude of vibration
What does sound require?
A medium to transfer energy
