Section 2 – Waves & EM Spectrum Flashcards
Recall that waves transfer energy and information without transferring matter
Describe evidence that with water and sound waves it is the wave and not the water or air itself that travels
• to travel from one place to another, the waves vibrate/oscillate
Definition of amplitude, wavelength, frequency, period
Amplitude - distance from equilibrium line to the maximum displacement (crest or trough)
Wavelength - the distance of one entire oscillation (the distance of a wave from one crest to another)
Frequency - the number of waves passing a certain point per second
Period - the number of seconds it takes for one full cycle .
Period = 1/frequency
Difference between transverse & longitudinal waves
TRANSVERSE WAVES
• the vibrations are perpendicular to the direction the wave travels.
• most waves are transverse —> all electromagnetic waves, S-waves, waves of strings (in guitar), ripples and waves in water
LONGITUDINAL WAVES
• the vibrations are parallel to the direction the wave travels.
• some regions of longitudinal waves are more spread/stretched out & other regions are more compressed due to the waves vibrating back and forth
• e.g: sound waves & seismic P-waves
Equations to calculate wave speed
1) Wave speed = frequency x wavelength
2) Wave speed = distance/time
Describe how to measure the velocity (speed) of sound in air and ripples on water surfaces
SPEED OF SOUND
Describe what happens to a wave when it reaches a material interface (boundary)
The wave is:
• REFLECTED - the wave bounces off the boundary
• REFRACTED - the wave changes direction as it passes into a new material due to its change in speed
• TRANSMITTED - waves passes through the material
• ABSORBED - the wave transfers energy to the material’s energy stores
Explain how waves will be refracted at a boundary in terms of change in direction & speed
• When a wave hits a boundary at an angle, the wave changes speed, and this causes a change in direction (refraction)
•The wave bends towards the normal the wave slows down, and away from the normal if it speeds up.
• wavelength decreases if wave slows down; wavelength increases if wave speeds up.
because light bends closer to the normal
Recall that different substances may absorb, transmit, refract or reflect waves in ways that vary with wavelength
How the Ear works
Ear canal —> Eardrum —> Tiny bones —> Tiny bones —> Cochlea —> Hairs —> Auditory nerve
• A sound wave enters the ear and causes the eardrum to vibrate
• These vibrations are transmitted through the ear
• and turned into electrical signals which are sent to your brain.
Recall that sound with frequencies greater than 20,000Hz is known as ultrasound
Recall that sound with frequencies less than 20Hz is known as infrasound
Explain uses of ultrasound & infrasound, including sonar, foetal scanning, exploration of the Earth’s core
Uses of ULTRASOUND:
• SONAR - a pulse of ultrasound is sent below a ship, and the time taken for it to reflect and reach the ship can be used to calculate the depth —> this is used to work out if there is a shoal of fish below the ship —> or how far the seabed is below the ship.
• FOETAL SCANNING - used to create an image of the foetus, allowing measurements to be made to check if the foetus is developing normally —> this works because ultrasound waves partially reflect at each surface boundary, this can be used to work out the distances and therefore produce an image of the foetus
USES of infrasound:
• can be used to EXPLORE THE EARTH’S CORE
There’s seismic waves inside the Earth (P-waves & S-waves)
• P-waves are longitudinal —> they travel through solids and liquids —> they travel faster than S-waves
• S-waves are transverse —> they only travel through solids —> slower than P-waves
Explain the difference between specular and diffuse reflection
Specular reflection is when waves are reflected in a single direction by a smooth surface (e.g. when light if reflected by a mirror)
Diffuse reflection is when waves are reflected by a rough surface. (E.g. paper) and the waves are reflected in all directions
Explain how the colour of light is related to a) differential absorption at surfaces b) transmission of light through filters
a) Opaque objects don’t transmit light. When visible light waves hit them, they absorb some wavelengths/colours of light & reflect others.
• a cucumber looks green because it reflects green light but absorbs all the other colours of light
b) When white light passes through a coloured filter, all colours are absorbed except for the filter colour. —> e.g. an orange filter transmits orange light but absorbs all the other colours
• an object appears black if it absorbs all the wavelengths/colours of visible light —> e.g. a red object appears black through a blue filter because all of the light reflected by the object will be absorbed by the blue filter
