Waves Flashcards
What is a wave
Waves can be used to transfer energy
What is a transverse wave?
A wave for which the oscillations are perpendicular to the direction of energy transfer.
What is a longitudinal wave?
A wave for which the oscillations are
parallel to the direction of energy
transfer.
Give two examples of transverse waves.
- Electromagnetic waves
- Seismic s-waves
Give two examples of longitudinal waves.
- Sound waves
- Seismic p-waves
What are the two parts of a longitudinal
wave called?
Compressions and rarefactions.
What is a wave’s amplitude?
The maximum displacement of a point
on a wave from its undisturbed position.
Height of a wave measured from equilibrium position to peak
What is wavelength?
● The distance from a point on a wave to
the same position on the adjacent
wave
● Most commonly peak to peak or
trough to trough
What is the frequency of a wave?
The number of waves that pass a given
point each second.
What is meant by a frequency of 200Hz?
200 waves pass a given point each
second.
What is wave speed?
The speed at which the wave moves or
at which energy is transferred through a
medium.
What word is used to describe when a wave
bounces off a surface?
Reflection
How do sound waves travel through a
solid?
The particles in the solid vibrate and
transfer kinetic energy through the
material.
What is the frequency range of human
hearing?
20 Hz - 20kHz
What are ultrasound waves?
Waves that humans cannot hear
What is a high pitch sound?
high frequency
What is a loud sound?
Big amplitude
What is the period of a wave
Time taken for one complete wave to pass
The law of reflection states that
angle of incidence = angle of reflection
What is the normal?
normal - an imaginary line at 90° to the surface.
What is called reflection from a smooth surface?
Reflection from a smooth, flat surface is called specular reflection. This is the type of reflection that happens with a flat mirror. The image in a mirror is:
upright
virtual
How is a specular reflection?
The image in a mirror is:
upright
virtual
What is a virtual image?
In a virtual image, the rays appear to diverge from behind the mirror, so the image appears to come from behind the mirror.
What is diffuse reflection?
If a surface is rough, diffuse reflection happens. Instead of forming an image, the reflected light is scattered in all directions. This may cause a distorted image of the object, as occurs with rippling water, or no image at all. Each individual reflection still obeys the law of reflection, but the different parts of the rough surface are at different angles.
What is refraction?
Different materials have different densities. Light waves may change direction at the boundary between two transparent materials. Refraction is the change in direction of a wave at such a boundary.
Why can refraction cause optical illusions?
Refraction can cause optical illusions as the light waves appear to come from a different position to their actual source.
Why does refraction happen?
The density of a material affects the speed that a wave will be transmitted through it. In general, the denser the transparent material, the more slowly light travels through it.
Glass is denser than air, so a light ray passing from air into glass slows down. If the ray meets the boundary at an angle to the normal, it bends towards the normal.
The reverse is also true. A light ray speeds up as it passes from glass into air, and bends away from the normal by the same angle.
A useful way of remembering the speed and direction changes of light during refraction is ‘FAST’: Faster - Away / Slower - Towards.
Do refracted waves have the same frequency?
Yes
Do refracted waves have the same wavelengths?
No because they travel at different speed
What are sound waves?
They are longitudinal waves. They are vibrations that travel through a medium
Can sound waves travel through a vacuum?
No
Why do we get an echo?
Sound waves can reflect off surfaces. We hear reflected sound as an echo.
Hard, smooth surfaces are particularly good at reflecting sound. This is why large, empty rooms produce lots of echoes.
Soft, rough surfaces are good at absorbing sound. This is why rooms with carpets and curtains do not usually produce lots of echoes.
What happens when sound waves reach the ear?
Sound waves make the eardrum vibrate and your ear sends signals to the brain
Why is human earing limited?
Because the conversion of sound waves to vibration of solids only works over a limited frequency range
How are objects detected in high water and to measure water depth below a ship?
Using Echo sounding. Pulses of high frequency sound waves are sent by a transmitter and reflected by the sea bed. The pulses are then detected by a receiver placed at the same hight as the transmitter. The time taken by the wave to reach the sea bed and back is measured.
What are ultrasounds used for?
Image of organs or prenatal scans
How do ultrasound scans work?
These uses rely on what happens when ultrasound waves meet the boundary between two different materials. When this happens:
some of the ultrasound waves are reflected at the boundary
the time taken for the waves to leave a source and return to a detector is measured
Advantages of using ultrasound waves vs x rays
- they reflect at boundaries between different type of tissues
- non ionising so harmless
What is an oscilloscope used for?
measure time taken by the wave to travel from the transmitter to the boundary and back
There are two types of seismic waves:
There are two types of seismic waves:
P-waves, which are longitudinal waves: they cause the first tremor after and earthquake and last about 1 minute
S-waves, which are transverse waves
Properties of P and S waves
P-waves S-waves
Type of wave longitudinal transverse
Relative speed faster slower
Can travel through solids and liquids solids only
Why are seismic waves important in science?
They allowed to study the structure of the earth
S-waves are not detected on the opposite side of the Earth what does this suggest?
S-waves are not detected on the opposite side of the Earth - this suggests that the mantle has solid properties, but the outer core must be liquid.
Why are P-waves are detected on the opposite side of the Earth.
Because they can travel through solids and liquids
Why do P waves refract at the boundary between mantle and outer core?
Their speed changes
Why do P and S waves bend as they travel through the mantle?
Their speed changes with depths and so their direction
What is a wavefront?
Imaginary line that connects all the same point in a set of waves
