Topic 6 waves GCSE Physics Flashcards
What happens when waves travel through a medium?
- the particles of the medium oscillate and transfer energy between each other
What is the amplitude of a wave?
- maximum displacement of a wave from its undisturbed position
What is the wavelength?
- distance between the same point of two adjacent waves (between the trough of one wave and the trough of another)
What is the frequency?
- number of complete waves passing a certain point per second
- measured in Hz
What can you find from the frequency?
- period of the wave
- so the amount of time it takes for a full cycle of the wave
How can you calculate the period of a wave?
period= 1/frequency
How are the vibrations in transverse waves?
- oscillations are perpendicular to the direction of energy transfer
What are some examples of transverse waves?
- all electromagnetic waves (light)
- ripples and waves in water
- a wave on a string
How are the vibrations in longitudinal waves?
- oscillations are parallel to the direction of energy transfer
What are some examples of longitudinal waves?
- sound waves in air (ultrasound)
- shock waves
What is wave speed?
- the speed at which energy is being transferred
What is the wave equation?
wave speed= frequency X wavelength
How can you use an oscilloscope to measure the speed of sound? - p24
1-set up the oscilloscope so the detected waves at each microphone are shown as separate waves
2- start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display (but have moved exactly one wavelength apart)
3- measure the distance between the microphone to find one wavelength
4- then use the formula wave speed = wavelength X frequency to find the speed
What is the speed of sound in air?
- 330 m/s
How can you measure the speed of water ripples using a lamp? p74
1- using a signal generator attached to the dipper of a ripple tank
2- use a lamp to see wave crests on a screen below the tank
3- the distance between each shadow line is equal to one wavelength, measure the distance between the shadow lines that are 10 wavelengths apart
4- use wave speed = frequency X wavelength to measure speed of waves
How can you use the wave equation for waves on a string?
p74 look at diagram
What are the three things that can happen when waves arrive at a boundary between two materials?
1- waves are absorbed by the material, this transfers energy to the materials energy store
2- the waves are transmitted, carry on travelling to new material
3- waves are reflected
What is the rule of all reflected waves?
angle of incidence = angle of reflection
What is the angle of incidence?
- angle between the incoming wave and the normal
What is the angle of reflection?
- angle between the reflected wave and the normal
What is the normal?
- imaginary line that’s perpendicular to the surface at the point of incidence
- shown with a dotted line
When does speculation reflection happen?
- happens when a wave is reflected in a single direction by a smooth surface
What is diffuse reflection?
- happens when a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions
Why does diffuse reflection happen?
- because the normal is different for each incoming ray which means the angle of incidence is different for each ray
What are all EM waves?
- transverse waves that transfer energy from a source to an absorber
What do all EM waves travel at?
- same speed through air or a vacuum
What do electromagnetic waves form?
- a continuous spectrum over a range of frequencies
How are electromagnetic waves grouped?
- into 7 different types
- based on their wavelength and frequency
What is the order of the electromagnetic spectrum from smallest to highest?
radio, micro, infrared, visible light, ultra violet, X-rays, gamma rays
Why is there such a large range of frequencies for the EM spectrum?
- because EM waves are generated by a variety of changes in atoms and their nuclei
What happens when a wave crosses a boundary between materials at an angle?
- the wave changes direction
- so its refracted
What does refraction in waves depend on?
- depends on how much the wave speeds up or slows down
- usually depends on the density of the two materials
What happens if a wave crosses a boundary and slows down or speeds up?
slows down- it will bend towards the normal
speeds up- bend away from the normal
What is the optical density of a material?
- measure of how quickly light can travel through it (bottom of pg 76 for ray)
How can you use transparent materials to investigate refraction?
1- place a transparent rectangular block on a piece of paper and trace around it, use a ray box or laser to shine a ray in the middle of one side of the box
2- trace the incident ray and mark where the light ray emerges
3- remove block and draw a straight line, join the incident ray and the emerging point to show the path of the refracted ray
4- draw normal where the light ray entered the block
5- measure the angle
How can you find out the amount of light that different materials reflect?
1- draw a straight line on a piece of paper
2- shine a ray of light at the objects surface and trace the incoming reflected light beam
3- draw a normal where the light hits the object
4- measure angle of incidence and angle of reflection
5- repeat experiment with different objects
What are EM waves made up of?
- oscillating electric and magnetic fields
What are alternating currents made up of?
- oscillating charges
- as the charges oscillate, they produce oscillating electric and magnetic fields (electromagnetic waves)
How can you produce radio waves?
- using an alternating current in an electrical circuit
What is a transmitter?
- object which changes oscillate to create the radio waves is called a transmitter
What happens when transmitted radio waves reach a receiver?
- they are absorbed
- energy carried by the waves is transferred to the electrons in the material of the receiver
- energy causes electrons to oscillate
- if receiver id part of a complete electrical circuit it generates an alternating current
What are radio waves?
- used mainly for communication
- EM radiation with wavelengths no longer than 10cm
Why can short-wave radio signals be received at long distances from the transmitter?
- at long distances from the transmitter
- because they are reflected from the ionosphere
What does Bluetooth use?
- short wave radio to send data over short distances between devices without wires
What can medium waves signals can reflect?
- reflect from the ionosphere depending on the atmospheric conditions and the time of day
What are radio waves used for?
- TV and FM radio transmissions (have very short wavelengths)