Waves Flashcards
(43 cards)
What is a wave?
A wave is something which transfers energy from one place to another without net movement of matter
What is the difference between a transverse wave and a longitudinal wave?
- In a transverse wave, the vibrations are at right angles to the direction of energy transfer
- In a longitudinal wave, the vibrations are parallel to the direction of energy transfer
Give examples of transverse waves
- All electromagnetic waves
- Waves on a string
- Seismic S-waves
Give examples of longitudinal waves
- Sound
- Ultrasound
- Compression waves on a slinky/spring
- Seismic P-waves
Where are the peaks and troughs on a wave?
- The peaks are the highest points on a wave
- The troughs are the lowest points
What is meant by the term “compression”?
A compression occurs when particles in the medium are pushed closer together as the wave passes
What is meant by the term “rarefaction”?
A rarefaction occurs when particles in the medium are pulled further apart as the wave passes
What are the 7 electromagnetic waves?
- Radio
- Microwave
- Infra-red
- Visible light
- Ultra-violet
- X-ray
- Gamma-ray
What is the wavelength of a wave? How can you measure it from a graph?
” just the physical length of the wave”
in TRANSVERSE WAVES:
it is measured by finding the distance between any two similar points on adjacent waves – e.g. peak to peak, or trough to trough
in LONGITUDINAL WAVES:
it is measured by finding the distance between adjacent compressions (or rarefactions) in a longitudinal wave
What is the amplitude of a wave? How can you measure it from a graph?
“Amplitude of a sound wave corresponds to the volume you hear”
in TRANSVERSE WAVES:
-Measure the height of the wave – from the resting position to the peak;
-the distance from trough to peak is double the amplitude
in LONGITUDINAL WAVES:
-from a point where the conc of particles is highest to when the conc is lowest
What is a period?
The time taken to complete one cycle of vibration (oscillation)
What is the frequency of a wave?
The number of vibrations (oscillations) per unit time at a point in the wave
- Measured in hertz (Hz)
- 1 Hz = 1 oscillation per second
What equation is used to calculate frequency?
Frequency = 1 / [period]
What is the equation for wave speed?
(Wave speed = distance/ time)
OR
(wave speed = frequency/ wavelength)
What happens when something is reflected?
- All or part of the wave energy is bounced off the surface
- The wave energy is called the “incident” wave
- the wave the bounces off the surface is called the “reflect” wave
What is the law of reflection?
When a wave energy is reflected there are 2 angles that can be calculated:
1) “i” is the incident angle: the angle between the normal and the direction of the incident wave
2) “r” is the reflected angle: the angle between the normal and the direction of the reflected wave
(the normal is an imaginary line drawn perpendicular to the surface)
The law states that:
[incident angle = reflected angle]
(Both rays and the normal must also lie in the same plane)
How does a rough surface affect a reflection?
NORMALLY with a SMOOTH surface:
-all the normals are parallel to one another -all the waves are reflected in an orderly way; images can be formed
when a surface is ROUGH:
- the normals at each point are in different directions
- each ray is reflected in a random direction
What is refraction?
When waves cross a boundary between two different media, 2 things can happen:
- If the light crossing the boundary is PARALLEL to the normal, it will slow down/ speed up, but continue straight through the new medium, with no change in direction
- If the light crossing the boundary is AT AN ANGLE, it will change direction; this is refraction
How does the medium affect the direction/ speed of refraction?
If a wave enters a MORE optically DENSE medium:
- it will slow down
- it will refract towards the normal (if it entered the boundary at an angle)
If a wave enters a LESS optically DENSE medium:
- it will speed up
- it will refract away from the normal (if it entered the boundary at an angle)
What is meant by the term “partial reflection”?How does this affect the measure of incident energy?
- This is what usually always happens; where not 100% of the incident wave energy is reflected
- At a boundary between two media some of the wave energy will be absorbed, some will be transmitted and some will be reflected;
- This needs to be taken into account when measuring incident energy using the formula:
[Incident energy = reflected energy + transmitted energy + absorbed energy]
How does reflection effect the direction, speed, frequency and wavelength of a wave?
- Changes the direction
- Speed is UNCHANGED
- Frequency is UNCHANGED
- Wavelength is UNCHANGED
How does refraction effect the direction, speed, frequency and wavelength of a wave?
if the wave enters a MORE optically DENSE medium:
- it will change direction; toward the normal
- It will slow down
- Frequency is UNCHANGED
- Wavelength decreases
if the wave enters a LESS optically DENSE medium:
- it will change direction; away from the normal
- It will speed up
- Frequency is UNCHANGED
- Wavelength increases
Describe how sound is produced
Sound waves are produced by a vibrating source, that causes the surrounding medium to vibrate- this pattern of vibrations travels away from the source as sound waves
How do the frequency, amplitude and speed of the sound waves, compare to the original vibrations from the source?
- The sound waves have the SAME FREQUENCY (or frequencies) as the vibrations of the source
- The AMPLITUDE of the sound waves depends on the amplitude of the vibrations of the source
- The SPEED of the sound waves is determined by the medium through which they travel and NOT by the source
