Waves Flashcards
What are waves
Waves are a way of transferring energy and information without transferring matter
What are the two types of waves
Transverse waves and longitudinal waves
What is a transverse wave
A transverse wave is a wave whose oscillations are perpendicular to the direction of motion
What is the crest of a wave
The crest of a wave is the point where the particles are at the top of their oscillation
What is the trough of a wave
The trough of a wave is the point where the particles are at the bottom of their oscillation
Give some examples of transverse waves
All waves of the Electromagnetic spectrum (radio waves, microwaves)
Secondary seismic waves
What is a longitudinal wave
A longitudinal wave is a wave whose oscillations are parallel to the direction of motion
What are the compressions of a wave
Compressions are high pressure areas where particles are close to each other
What are the rarefactions of a wave
Rarefactions are low pressure areas where particles are further apart
Give some examples of longitudinal waves
Sound waves
Primary seismic waves
What is the amplitude of a wave
The amplitude of a wave is the maximum displacement from equilibrium (measured in m)
What is the wavelength of a wave
The wavelength is the distance between a particular point on a wave and the same point on the next wave
Define frequency
Frequency is the number of waves produced each second
Give the equation for frequency
Frequency (Hz) = number of waves/time
Define the time period
Time period is the time taken for one complete oscillation
State the equation that links frequency with time period
Frequency = 1 / time period
A generator produces 48 waves in 12 seconds. Calculate the frequency of the waves
f = w / t
f = 48 / 12
f = 4 Hz
A generator produces 48 waves in 12 seconds. Calculate the time period of the wave
f = 4 Hz
T = 1 / f
T = 1 / 4
T = 0.25s
What is a wavefront
A wavefront is a line on a wave where all vibrations are on the same position
State the equation for wave speed
Wave speed = frequency(Hz) * wavelength(m)
What is the speed of a wave with a frequency of 2.5kHz and wavelength of 50 cm
s = f * λ
s = 2500 * 0.5
s = 1250 m/s
What is the doppler effect
The doppler effect is the apparent change in the frequency of a wave caused by the relative motion between the source and the observer
Explain how the sound heard by a student throwing a buzzer away from him changes
The sound heard from the student changed due to the doppler effect. As the buzzer started to move away, the observed wavelength increased, the wavefronts were further apart and the frequency decreased, while the wave speed remained constant
What are mechanical waves
Mechanical waves are waves that require a medium in order to propagate. They cannot transmit energy through vacuum
Give some examples of mechanical waves
Sound waves
Water waves
What are electromagnetic waves
Electromagnetic waves are waves that can transmit energy through vacuum. They do not require a medium in order to propagate
What separates the waves of the electromagnetic spectrum
The waves of the electromagnetic spectrum are separated by their different wavelengths and frequencies
What is the color spectrum of visible light waves called
ROYGBIV
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Name all the waves of the electromagnetic spectrum in terms of increasing frequency
radio waves
microwaves
infrared waves
visible light waves
ultraviolet waves
x-rays
gamma rays
What are the common properties of electromagnetic waves
They carry energy and information
They are transverse waves
They can travel through vacuum at the speed of light
They can all be reflected and refracted
What are the uses and dangers of Gamma rays
Uses: They are used to sterilize equipment as they can kill bacteria
Dangers: Mutation of DNA can cause cancer
What are the uses and dangers of X-rays
Uses: Observing internal structures of objects and materials as they can penetrate soft tissues but not bones
Dangers: Mutation of DNA can cause cancer
What are the uses and dangers of Ultraviolet waves
Uses: Detecting security ink as it fluoresces with UV light
Dangers: Blindness
What are the uses and dangers of Visible light waves
Uses: Optical fibres as they can undergo total internal reflection
Dangers: High intensity light can damage eyes
What are the uses and dangers of Infrared waves
Uses: Optical fibres as they can undergo total internal reflection
Dangers: Skin burns
What are the uses and dangers of Microwaves
Uses: Satellite communication because they can penetrate the Earth’s atmosphere
Dangers: Internal heating of body tissue
What are the uses and dangers of Radiowaves
Uses: Long range communication because they can be reflected from the Earth’s atmosphere
Dangers: Radio waves have no danger :)
What are luminous objects
Luminous objects are objects that emit their own light
What are non-luminous objects
Non-luminous objects are objects that do not emit their own light
Give two examples of luminous and non-luminous objects
Luminous: Sun, light bulbs
Non-luminous: desks, walls
What does the law of reflection state
The law of reflection states that when a light ray strikes a plane mirror, it is reflected so that the angle of incidence is equal to the angle of reflection
Which angle is the angle of incidence
The angle of incidence is always the angle between the incident ray and the normal
What is the normal line
The normal is an imaginary line drawn perpendicular to the plane mirror
What is refraction
Refraction is the change in the direction of a wave at the boundary between two media due to a change in speed
What happens when light enters a more dense medium
When light enters a more dense medium, it slows down and bends towards the normal
What happens when light enters a less dense medium
When light enters a less dense medium, it speeds up and bends away from the normal
What happens if the incident ray strikes the boundary between two media at 90 degrees
The ray will continue without a change of direction. This is because the angle of incidence is 0, so the angle of refraction will be also 0
State three ways in which light waves change as they pass into another medium
Change of speed
Change of direction
Wavelength decreases
What is the refractive index
The refractive index is a number that expresses the ability of a medium to bend light
What is the refractive index of water
1.3
What is the refractive index of glass
1.5
State the equation used to calculate the refractive index of a medium
n = sin i / sin r
*this can only be used when traveling from air to a denser medium
Describe the experiment used to calculate the refractive index of a glass block
Shine a ray of light through a glass block using a light box. Mark the positions of the incidence and refracted rays on the piece of paper and draw the refracted ray using a pencil. Using a protractor, measure the angle of incidence and the angle of refraction. Repeat this for many different values of the refractive index. Then she should find the sine of the two values and calculate their ratios by diving the sine of the angle of incidence with the sine if the angle if refraction in order to find the refractive index. She could also plot a graph with the values of sin i and sin r and measure the gradient to find the refractive index
What is total internal reflection
Total internal reflection is the total reflection of light that occurs when moving from an area of high density to one of low density, while the angle of incidence is bigger than the critical angle
What is the critical angle
The critical angle is the angle of incidence that offers an angle of refraction of 90 degrees
What is the equation for the critical angle
sin c = 1 / n
What is total internal reflection used for
Binoculars
Optical fibres
Periscopes
What do optical fibres do
Optical fibres use total internal reflection to contain and guide light
Give two uses for optical fibres
Fibre broadband sends computer information coded as pulses of light along underground optical fibres
Doctors can look at the inside of their patients using an endoscope
What is dispersion
Dispersion occurs when white light passes through a prism and emerges out as a band of different colors
Why does dispersion occur
Dispersion occurs because the different colors of white light travel in the glass prism at different speeds, and they thus are refracted by different amounts
What is the human audible range
20Hz - 20000Hz
What are ultrasound waves
Waves above the audible range
What are infrasound waves
Waves below the audible range
What does the loudness of a sound depend on
The amplitude
What does the pitch of a sound depend on
The frequency
What do we use to display a sound wave
An osciloscope
How does SONAR work
SONAR helps calculate the depth of water. Sound pulses are emitted towards the seabed, they reflect and their echo is received. The time between emission and return of the echo is recorded. Since we know both the time and the speed of sound in water we can calculate its depth
