waves Flashcards
transverse waves
wavelength: crest to crest or trough to troughamplitude: half the height of the wavefrequency: the number of waves passing a point each second (Hz)Period(T): time for one wave to pass (s0
frequency
f= 1/period or f=1/t
law of reflection
-when a wave reflects, the angle of incidence (i) equals the angle of reflection (r)- angles of incidence are always measured with respect to the normal
why can you see your face in a mirror but not on a brick wall?
on rough surfaces, light is scattered in random directions and so an image can not be seenon smooth surfaces the light is all reflected in the same direction and an image is formed
refraction of light
-when light travels from a less dense medium into a denser medium it slows down and bends towards the normal-when the light leaves the glass block it speeds up and bends away from the normal
why does light bend?
when the wave enters the denser medium, thee side entering slows down first and drags the wave around
find the refractive index of a material(experiment)
1) place a perspex block in the centre of a piece of paper and draw round it. Draw in a normal and label point A.
2) Draw a line(BA) which goes to the normal and stops at the edge of the block which has an angle of incidence of 20 degrees (i=20)
3) shine a ray along BA through the block, making sure it passes through point A
4) Mark point X where the ray leaves the block. take the block away and draw line AX. Measure the angle of refraction and enter it in a table.5)repeat for different angles of incidence from 0 to 90 degrees by drawing further lines BA and AX
6) calculate values of sin i and sin r and enter them in the tale, giving your values to 4 decimal places
7) plot a graph of sin i (y axis) against sin r (x axis) and draw a line of best fit.
8) calculate the gradient of the line of best fit- this is your estimate for the refrative index of the material
snell’s law
n = sin i / sin r - the bigger the refractive index (n) the more refraction occurs
total internal refraction
when a ray of light travelling through a denser medium is reflected when the angle of refraction is 90 degrees occurs when the angle of refraction is greater than 90 degrees n= 1/sin C or sin C= 1/n c= critical angle
what can TIR be used for ?
to send light down optical fibres
wave equation
v=fd
v=velocity
f=frquency
d=distance
real and virtual images
- real images can be projected on a screen- virtual images cannot be projected on a screen- the distance of the virtual image behind the mirror is the same as the actual distance of the object in front of the mirror
analogue and digital signals
analogue signal= data can have any value
digital signal= data can only have certain values
