Unit 6 - Waves Flashcards
Unit of measure for frequency
Hertz (Hz)
Longitudinal waves
The vibrations are parallel to the direction of travel.
Eg sound waves
Transverse waves
The vibrations are perpendicular to the direction of travel
Eg light waves, surface water waves
What is amplitude
Amplitude is the height (or depth) of the crest measured from the midpoint
More amplitude = louder sound
What is frequency
Frequency is the number of waves passing a point each second
Measured in Hz
Higher frequency = higher pitched sound
What is the wavelength
The distance (in meters) from one waves crest to the next waves crest. Measured in λ (lambda)
What is the period of a wave
Time period of a wave is the time taken for one complete wave to pass (bottom to top to bottom)
Measured in seconds
Wave speed (m/s) =
Wave speed (m/s) = frequency (Hz) X wavelength (m)
How do waves transfer energy
Waves transfer energy without transferring matter
Time period (s) =
Time period (s) = 1 / frequency (Hz)
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 diffraction depends on the wavelength and physical properties of the gap
What can cause as wave to diffract
Passing through a gap
Pass an edge
Properties of light waves
Transverse wave
Can be reflected, refracted, and diffracted
Law of reflection
Angle of incidence (coming into the normal) equals the angle of reflection (leaving the normal)
What is rarefaction
Refraction is the bending of light when it enters a material of a different density.
Light refracts towards the normal when entering a higher density and away from the normal when entering a lower density.
What is the angle of incidence
The angle at which the light enters the material
measured from the normal
What is the angle of refraction
The angle that the light travels at once it has entered the new material
measured from the normal
What is the refractive index
The ratio of the velocity of light in a vacuum to its velocity in a specified medium (object)
Equation for refractive index
n = sin(i) / sin(r)
i is the angle of incidence
r is the angle of refraction
What is total internal reflection
Total internal reflection is the complete reflection of a light ray inside a Perspex wire
Describe the role of total internal reflection in transmitting information along optical fibres
Behind 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. You can use this to send information down optical fibres
What is the critical angle (c)
Once the angle of incidence reaches a certain point, the light will simply be refracted back into the medium. This point is the critical angle
Equation for critical angle
Sin(c) = 1 / n
n is the refractive index
c is the critical angle
Properties of sound waves
Longitudinal waves
can be reflected, refracted, and diffracted
What is light
Light is a part of a single electromagnetic spectrum
This includes radio, microwave, infrared, visible, X-ray, ultra violet and gamma rays
All of these travel at the same speed
The order of the electromagnetic spectrum starting at the highest frequency and decreasing
Gamma ray, X-ray, ultraviolet, visible, infrared, microwave, radio
The order of the electromagnetic spectrum starting from the smallest wavelength and increasing
Gamma ray, X-ray, ultraviolet, visible, infrared, microwave, radio
Uses of radio waves
Broadcasting and communications
Uses of microwaves
Cooking and satellite transmissions
Uses of infrared
Heaters and night vision equipment
Uses of visible light
Optical fibres and photography
Uses of ultraviolet light
Fluorescent lamps
Uses of X-rays
Observing the internal structure of objects and materials and medical applications
Uses of gamma rays
Sterilising food and medical equipment
Detrimental effects of excessive exposure to microwaves and how to prevent it
Internal heating of body tissue
Avoid it by moving further away
Detrimental effects of excessive exposure to infrared and how to prevent it
Skin burns
Avoid it by wearing SPF
Detrimental effects of excessive exposure to ultraviolet and how to prevent it
Damage to surface cells and blindness
Avoid it by wearing protective clothing
Detrimental effects of excessive exposure to gamma rays and how to prevent it
Cancer and cell mutation
Avoid it by wearing protective clothing and increasing distance from the source
What is meant by an analogue signal
An analogue signal can constantly vary in frequency and amplitude, eg a persons voice
What is meant by a digital signal
A digital signal is binary and can only be a 1 or a 0, eg a modern radio signal
What is the benefit to transmitting data in the digital format
All signals lose definition when transmitted and need to be amplified. When amplified, and analogue signal will remain unclear and is difficult to clarify whereas a digital signal can only be a 1 or 0 so it is easy to amplify and regain clarity
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.
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.
How digital signals carry more information
They have a larger bandwidth
What is the frequency range of 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.
How an oscilloscope and microphone can be used to display a sound wave
A microphone converts sound energy into electrical energy in the form of electronic signals. A computer or an oscilloscope can be used to display these electronic signals, which show the same changes in amplitude and frequency as the sound waves.
Describe an experiment using an oscilloscope to determine the frequency of a sound 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.
