P12- Wave properties Flashcards
Mechanical waves
Examples?
Key feature?
What type?
Sound waves, water waves, seismic waves
Travel through a medium
Can be transverse or longitudinal
Electromagnetic waves
Examples?
Key feature?
What type?
Light waves, radio waves microwaves
Can travel through a vacuum (no medium is needed)
All are transverse waves
What do waves transfer?
Energy and information without transferring matter, as the substance itself doesn’t travel
Transverse waves
Direction of oscillations?
Examples?
Oscillates perpendicular to the direction of the energy transfer
Radio waves, light waves, water waves
Longitudinal waves
Direction of oscillations?
Examples?
Oscillates parallel to the direction of the energy transfer
Sound waves, ultrasound waves
Amplitude
Def?
How does it relate to energy?
Where is it on a graph?
The maximum displacement of a point of a wave from its rest position
The bigger the amplitude, the more energy it carries
Difference between rest and peak
Wavelength
Def?
Wave speed
Def?
Distance from one point on a wave to another (trough to trough or peak to peak)
Distance travelled by each wave every second through a medium
Frequency
Def?
Unit?
Period?
Calculation?
Number of waves passing a fixed point every second
hertz (Hz)
Time taken for each wave to pass a fixed point
period (s) = 1 / frequency
Measuring the speed of sound in the air
Person A stands at a long, measured distance from Person B, but still in sight, they crash two cymbals together and Person B times the interval between seeing it and hearing it. Calculate speed using speed= distance/ time
What happens to a plane wave when it crosses a boundary at an angle?
Each wave changes speed, wavelength and direction, but has the same frequency
Plane waves when reflected from a straight barrier
Key fact and why?
Reflected at same angle because speed and wavelength doesn’t change
What happens to a substance when waves are directed at it?
Some or all of the wave may be reflected. Substance can be heated as it gains energy from the absorbed waves
Density affecting waves?
The denser the object, the more slowly light passes through it
How to find the frequency of waves from a ripple tank?
Count the number of waves passing through a point in 10 seconds and divide no of waves by 10.
How to find wavelength, frequency and wave speed in a ripple tank?
-Sheet of white card under tank
-Adjust rod to touch surface of water
-Switch and adjust lamp and motor until pattern is shown
-Measure total length of pattern, and divide by no of waves to find wavelength
-Count no of waves passing a point in 10s and divide no of waves by 10 to find frequency
-Use wave speed= frequency x wavelength
How to find wavelength, frequency and wave speed on a string?
-Set up string suspended between a bridge and generator
-Switch on signal generator, adjust tension of spring until it shows a pattern
-Use ruler to measure length between bridge and generator
-Divide total length by no of half waves
-Multiply by 2 to find wavelength
-Frequency shown by signal generator
-Use wave speed= frequency x wavelength
Investigating wave speed practical
-Fill tray with small amount of water
-Gently drop one side
-Measure distance the wave travels and time it takes
-Calculate speed= distance / time
High frequency=?
High amplitude=?
High pitch
High volume
The ear
Can hear between what frequency range?
How do we hear?
Why is human hearing limited?
20-20,000 kHz
Sound waves make ear drum vibrate, send signals to brain
The conversion of sound waves to vibrations of solids only work up to a frequency range
Ultrasound waves
Sound waves with a frequency greater than 20,000 Hz, so humans can’t hear
What is echo sounding and what is it used for?
Using high-frequency sound waves to detect objects in deep water or depth below ship
How do ultrasound scanners work?
Ultrasound waves are partially reflected from tissue boundaries and return at different times to build an image of tissue boundaries on a screen.
2 advantages of using ultrasound waves?
-Can scan organs and other tissues in the body
-Non-ionising, so is harmless
Layer of the Earth and their states of matter?
Inner core= solid
Outer core= liquid
Mantle= solid
Crust= solid
Seismic waves
Waves that travel through the Earth
Focus def?
Epicentre def?
Where an earthquake originates from
The nearest point on the surface to the focus
2 types of seismic waves?
also called?
type of waves?
Primary waves (P-waves)– longitudinal
Secondary waves (S-waves)– transverse
Primary waves and secondary waves
Cause?
What do they do?
Initial tremors that last around 1 min, push or pull on material
Tremors a few minutes later, shake the material from side to side
P and S waves when in the Earth?
3 key facts
-Both bend as travel through mantle, change in speed due to changing depth, so direction changes
-P-waves refract at mantle and outer core boundary
-S-waves can’t travel through liquid outer core
