waves Flashcards
what is a longitudinal wave
oscillations are in the same direction as the energy transferred by the wave
eg: sound
what is a transverse wave
oscillations are perpendicular to the direction of the energy transferred by the wave
eg: light
explain the dopler effect
waves produced by a source which is moving towards/away from an observer will appear to have a different wavelength than they would if they were stationary.
the wave speed is constant so if the source is moving, it catches up to the waves in front; the waves in-front bunch up and the waves behind spread out.
- the frequency of a source moving towards you will seem higher and the wavelength will seem shorter (and vice versa)
describe the role of total internal reflection in transmitting information along optical fibres
the core of the fibre is so narrow that light signals always passing through it always hit the glass at an angle higher than C, so are totally internally reflected
describe the role of total internal reflection in prisms
the ray of light travels into one prism where it is totally internally reflected by 90 degrees.
It then travels into another prism lower down and is refracted 90 degrees again
the light ends up travelling parallel to its original path but at a different height
relationship between refractive index and angle of incidence and refraction
n =sin i/sin r
relationship between refractive index and critical angle
n= 1/sinc
what is the order of the electromagnetic spectrum (longest-shortest wavelengths)
radio, micro, infrared, visible, UV, Xray, gamma
use of radio waves
communications + broadcasting
use of microwaves
cooking + satellite transmissions
use of infrared
heaters+ night vision
use of visible light
optical fibres, photography
use of UV light
fluorescent lamps
use of Xray
observing internal structure of objects
use of gamma rays
sterilising food and equipment; cancer treatment
dangers of microwaves and infrared
micro: internal heating of body tissue
infrared: skin burns
dangers of ultraviolet waves
damage to surface cells and blindness
dangers of gamma rays
cancer, mutation and simple protective measures against risks
describe a method to find the refractive index of a block of glass
draw around block; mark positions of incident and emergent rays; (remove block and) draw refracted ray; measure i; measure r; measure angle(s) to the normal; range of values; plot (graph of) sin i against sin r; graph is straight line; gradient gives refractive index;
what is wavelength
distance between two peaks
what is frequency
how many complete waves there are per second
what is amplitude
height of the wave from rest(middle) to crest (top)
what is the period
the time taken for a complete wave to pass a point
wave speed formula
wave speed = frequency x wavelength
what do all waves do
transfer energy and information without matter
what properties do all electromagnetic waves share
all are transverse
all travel at the same speed in a vacuum
in visible light, which colours have the longest/ shortest wavelength
red= longest wavelength, lowest frequency violet= shortest wavelength, highest frequency
what is the law of reflection
angle of incidence= angle of reflection
what is a virtual image
an image that cannot be formed on a screen
what is refraction
waves changing speed or direction
what happens to EM (eg light) waves as they enter a different medium
they are refracted
they travel more slowly in a denser medium
eg when light enters a glass block it goes slower
in what direction is the light refracted when it goes in and out of a glass block
going into the block= denser medium so travels slower, so travels closer TO the normal
going out of the block= less dense medium so travels slower, so travels AWAY from normal
FAST ( faster= away; slower= towards)
what happens to sound waves as they enter a different medium
going into denser medium= speed up
opposite to light waves
