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
S-waves
Transverse waves
Can travel through solids only
Slower than P-waves
Electromagnetic waves
They are transverse waves that transfer energy from the source of the waves to an absorber
They form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum (space) or air
Electromagnetic spectrum
Radio waves (long wavelength — low frequency — lowest energy)
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays (short wavelength — high frequency — highest energy)
Properties of electromagnetic waves (1)
Properties of electromagnetic waves (2)
How different surfaces affect infrared intensity practical
Place a Leslie cube on a heat-resistant mat
Fill it, almost to the top, with boiling water and replace the lid
Leave for one minute, this is to enable the surfaces to heat up to the temperature of the water
Use the infrared detector to measure the intensity of infrared radiation emitted from each surface or the temperature of the surface
Make sure that the detector is the same distance from each surface for each reading
Radio waves
Used for TV’s and radios
Microwaves
Used for satellites and cooking food
Infrared
Used for electrical heaters, cooking food, infrared cameras
Visible light
Used for fibre optic communications
Ultraviolet
Used for energy efficient lamps, sun tanning
X-rays and gamma rays
Used for medical imaging and treatments
Converging lens (convex)
Forms an image by refracting light
Parallel rays of light converge to the principal focus
The distance from the lens to the principal focus is called the focal length
The image produced by a convex lens can be either real or virtual
Diverging lens (concave)
Forms an image by refracting light
Parallel rays of light diverge from a principal focus
The image produced by a concave lens is always virtual
Magnification
Image height / object height
Transparent objects
Transmits the light through the object, some of it refracts
Translucent objects
Transmits light through but is scattered or refracted
Object has internal boundaries that repeatedly change the direction of light
Opaque objects
Absorb all light that hits it, reflects all of it or scatters it on a surface
White light
White light can be split up to produce a spectrum containing all the different colours of visible light
White light can be split up into a spectrum of colours using a prism
Red, green and blue make white light
White surfaces reflect all colours of light
Black light
Black surfaces absorb all colours of light
