Waves and the Electromagnetic Spectrum Flashcards
describe longitudinal waves in terms of oscillation
oscillations parallel to the direction of travel
describe transverse waves in terms of their oscillation
perpendicular to the direction of wave travel
give 3 examples of longitudinal waves
- sound waves
- ultrasound waves
- seismic P-waves
give 5 examples of transverse waves
- ripples on the surface of water
- vibrations in a guitar string
- a Mexican wave in a sports stadium
- electromagnetic waves - eg light waves, microwaves, radio waves
- seismic S-waves
define amplitude
the maximum displacement of a point of a wave from its rest position
define wavelength
distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough
define frequency
the number of waves passing a point each second
define time period (in waves)
the time taken for a full cycle of the wave, usually measured from peak to peak, or trough to trough
define wave speed
the distance the wave travels in a given amount of time
describe a method for measuring the speed of sound waves in air
A person fires a starting pistol and raises their hand in the air at the same time. A distant observer stood 400 metres (m) away records the time between seeing the action (the light reaches the time keeper immediately) and hearing the sound (which takes more time to cover the same distance).
how is frequency related to sound
- high frequency sound waves are high pitched
- low frequency sound waves are low pitched
how is amplitude related to sound
*high amplitude sound waves are loud
*low amplitude sound waves are quiet
what is an electromagnetic wave?
A transverse wave caused by oscillations in an electromagnetic field
how is the electromagnetic spectrum grouped?
a spectrum containing seven groups going from very long wavelength, low frequency and low energy to very short wavelength, high frequency and high energy
list the groups of electromagnetic waves in order of decreasing wavelength and increasing frequency/ energy
- radio waves
- microwaves
- infrared
- visible light
- ultraviolet
- x-rays
- gamma rays
why can our eyes only detect visible light?
because our eyes can only detect a limited range of electromagnetic waves and visible light contains all the frequencies that can be detected by the human eye.
what colour has the lowest frequencies of visible light?
red
what colour has the highest frequencies of visible light?
violet
what is refraction?
a process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens
* change in material
* causes change in direction
* causes change in speed
how are radio waves produced?
by oscillations in electrical circuits
what can radio waves be absorbed by?
electrical circuits
what do changes in atoms and the nuclei of atoms result in?
electromagnetic waves being generated or absorbed (over a wide frequency range)
what is the angle of refraction less than?
the angle of incidence
what is the angle of incidence?
the angle between the normal line and incident ray
what is the angle of refraction?
the angle between the normal line and the refracted ray
what is the incident ray?
the light ray going into/ pointed at an object
hazard of radio waves
very small rise in temperature
hazard of microwaves
can cause internal heating of body tissues
hazard of infrared
radiation is felt as heat and causes skin to burn
hazard of visible light
from a laser which is very intense can damage the retina at the back of the eye
hazard of ultraviolet
can damage skin cells and lead to skin cancer and damage the eyes, it can cause skin to age prematurely
hazard of x-rays
damage cells inside the body causing dangerous ionisation in living cells which damages DNA which can lead to cancer
hazard of gamma rays
damage cells inside the body causing dangerous ionisation in living cells which damages DNA. This can lead to cell death and cancer.
use of radio waves
communication
why are radio waves used for communication?
because they are transmitted easily through air, don’t cause damage if absorbed by the human body, and can be reflected to change direction.
uses of microwaves
cooking food and for satellite communication
why are microwaves used for cooking food and for satellite communication?
- they’re high frequency so easily absorbed in food, increasing the internal energy of the food molecules
- they pass easily through the atmosphere, so they can pass between stations on Earth and satellites in orbit
uses of infrared
electrical heaters, cookers, infrared cameras which detect people in the dark
why is infrared used for electrical heaters, cookers, infrared cameras which detect people in the dark?
- it has frequencies which are absorbed by some chemical bonds, the internal energy of the bonds increases when they absorb infrared light
- all objects emit infrared light but the human eye cannot see this light but infrared cameras can detect it so ‘thermal imaging’ is useful for detecting people in the dark
uses of visible light
fibre optic communications
why is visible light used for fibre optic communications?
because our eyes can detect it’s wavelengths
uses of ultraviolet
energy-efficient lamps
why is ultraviolet used for energy-efficient lamps?
fluorescent substances in the lamps absorb ultraviolet light produced inside the lamp, and re-emit the energy as visible light
uses of x-rays and gamma rays
internal imaging
why are x-rays and gamma rays used for internal imaging?
because they are transmitted through body tissues with very little absorption and X-rays are absorbed by dense structures like bones, which is why X-ray photos are used to help identify broken bones
how do wave front diagrams work?
- as a wave travels into a denser medium, such as water, it slows down and the wavelength decreases.
- Although the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter.
- if for example the right hand side of the incoming wave slows down before the left hand side does. This causes the wave to change direction.
