Waves Flashcards
Transverse waves
A wave that oscillates perpendicular to the direction of energy transfer
E.g. electromagnetic waves
Longitudinal waves
A wave that oscillates parallel to the direction of energy transfer
E.g. sound waves in air
Amplitude
The maximum displacement of a wave peak to its undisturbed position
The bigger the amplitude the more energy the waves carries
Wavelength
The distance from a point on one wave to the same point on the next wave
Frequency
The number of waves passing a point each second
Period
The time taken for each wave to pass a specific point
Period formula
1 / frequency
Wave speed
The speed at which the energy is transferred (or the wave moves) through a medium
Wave speed formula
Frequency x wavelength
Measuring waves in a ripple tank practical
Set up the ripple tank as shown in the diagram with about 5 cm depth of water
Adjust the height of the wooden rod so that it just touches the surface of the water
Switch on the lamp and motor and adjust until low frequency waves can be clearly observed
Measure the length of a number of waves then divide by the number of waves to record wavelength
Count the number of waves passing a point in ten seconds then divide by ten to record frequency
Reflection
Reflection of waves
Waves can be reflected at the boundary between two different materials causing echoes
Law of reflection
Angle of incidence = angle of reflection
Specular reflection
Reflection in which light travelling towards a surface in one direction is all reflected in a single direction
E.g. a mirror
The image in a mirror is upright and virtual
Diffuse reflection
When light is reflected off a surface and is scattered in different directions
Causes a distorted image, e.g. rippling water
Reflection of light on different surfaces required practical
Place a glass block onto an A3 sheet of paper and trace around it using a pencil
Using a ray box shine a light perpendicular to the block and draw a dotted line on either side of the block where the light enters and exits
Label this line as ‘N’ indicating the normal
Then use the ray box to shine a ray of light at the point where the normal meets the block
Draw a dotted line for where the light enters and exits
Calculate the angle of reflection, angle of incidence and angle of refraction
Repeat this whilst increasing the angle of incidence in 10 degree increments until 70 degrees
Refraction
A process whereby a wave changes speed and sometimes direction upon entering a denser or less dense medium
Refraction of waves
As a wave enters a different medium (e.g. air into glass), the light wave loses energy as glass is denser than air, and therefore loses speed and bends away from the normal
Sound waves
Can travel through solids causing vibrations in the solid
Sound travels faster in solids than in liquids and gases
Cannot travel through space, because space is a vacuum (there are no particles to carry the vibrations)
Range of human hearing
20 Hz to 20 kHz
Ultrasound waves
Has a frequency higher than the upper limit of hearing for humans
Partially reflected at a boundary between two different media
Uses of ultrasound waves
The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is, allowing ultrasound waves to be used for both medical and industrial imaging
Echo sounding
When high frequency sound waves is used to detect objects in deep water and measure water depth
Distance = speed of sound in water × time taken
P-waves
Longitudinal waves
Can travel through liquids and solids
Faster than S-waves
