Section 2: Waves & the Electromagnetic Spectrum Flashcards
What do waves transfer?
Energy and information
What is frequency?
Number of complete cycles of the wave passing a certain point each second
What is a period?
Amount of time it takes for a full cycle of a wave
How to calculate a period?
1/frequency
What is amplitude?
Maximum displacement of a point on a wave from its rest position
What is wavelength?
Length of a full cycle of a wave
Properties of transverse waves?
- Oscillate perpendicular to the direction that the wave travels
- Carry energy and information
Examples of transverse waves?
- Electromagnetic waves
- S-waves
- Ripples in water
Properties of longitudinal waves?
- Oscillate parallel to direction in which the wave travels
- Transfer energy and information
Examples of longitudinal waves?
- Sound waves
- P-waves
What can happen to a wave when it hits a boundary?
Absorbed
Reflected
Transmitted (either being refracted or not refracted)
What is reflection?
When the wave is reflected in the opposite direction
What is the law of reflection?
Angle of incidence = angle of reflection
What is refraction?
When a wave changes speed and direction as it crosses a boundary between two materials at an angle to the normal
What will happen if the waves slows down when it refracts?
Wave refracts —> slows down —> wavelength decreases —> wave bends towards normal
What will happen if the waves speeds up when it refracts?
Wave refracts —> speeds up —> wavelength increases —> wave bends away from the normal
What do electromagnetic materials do when refracted depending on density of material?
Slow down in denser materials
Speed up in less dense materials
What is total internal reflection?
When all light incident on a boundary is reflected back
What is the critical angle?
The minimum angle at which the total internal reflection occurs
What happens when the critical angle is larger than the angle of incidence?
The wave is mostly refracted, some reflected
What happens when the angle of incidence is larger than the critical angle?
There is total internal reflection
How do vibrations work in air?
- Vibrating object creates sound waves
- Sound waves travel as a series of compressions and refraction through air
How do vibrations pass through solids?
- Vibrating object creates sound waves
- Sound waves hitting solids cause the particles in the solid to vibrate
- Particles will then hit the next particles in line and so on - sound waves travel through the solid as these vibrations
How is sound heard?
- Sound waves reach ear
- This causes eardrum to vibrate
- These vibration cause other parts of ear to vibrate, allowing you to hear the sound waves
What is limited frequency range?
When conversion of sound waves to vibration in solids only occur over a certain frequency range
What are the limiting factors of frequency ranges in solid objects?
Size
Shape
Structure
What are ultrasound waves?
Sound waves with frequencies higher than 20,000Hz
What is ultrasound used for?
Medical scans e.g. pre natal scanning of foetus
Echo sounding (sonar) e.g. finding depth of water or locating objects in water
What are infrasound waves?
Sound waves with frequencies lower than 20Hz
What are P-waves?
Seismic waves that give evidence of the size of earths core and its structure
What are properties of P-waves?
Longitudinal waves
Travel through solids and liquids
What are S-waves?
Seismic waves that give evidence of the size of earths core and its structure