waves

Question 1

what is a longitudinal wave

Answer 1

oscillations are in the same direction as the energy transferred by the wave
eg: sound

Question 2

what is a transverse wave

Answer 2

oscillations are perpendicular to the direction of the energy transferred by the wave
eg: light

Question 3

explain the dopler effect

Answer 3

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)

Question 4

describe the role of total internal reflection in transmitting information along optical fibres

Answer 4

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

Question 5

describe the role of total internal reflection in prisms

Answer 5

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

Question 6

relationship between refractive index and angle of incidence and refraction

Answer 6

n =sin i/sin r

Question 7

relationship between refractive index and critical angle

Answer 7

n= 1/sinc

Question 8

what is the order of the electromagnetic spectrum (longest-shortest wavelengths)

Answer 8

radio, micro, infrared, visible, UV, Xray, gamma

Question 9

use of radio waves

Answer 9

communications + broadcasting

Question 10

use of microwaves

Answer 10

cooking + satellite transmissions

Question 11

use of infrared

Answer 11

heaters+ night vision

Question 12

use of visible light

Answer 12

optical fibres, photography

Question 13

use of UV light

Answer 13

fluorescent lamps

Question 14

use of Xray

Answer 14

observing internal structure of objects

Question 15

use of gamma rays

Answer 15

sterilising food and equipment; cancer treatment

Question 16

dangers of microwaves and infrared

Answer 16

micro: internal heating of body tissue
infrared: skin burns

Question 17

dangers of ultraviolet waves

Answer 17

damage to surface cells and blindness

Question 18

dangers of gamma rays

Answer 18

cancer, mutation and simple protective measures against risks

Question 19

describe a method to find the refractive index of a block of glass

Answer 19

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;

Question 20

what is wavelength

Answer 20

distance between two peaks

Question 21

what is frequency

Answer 21

how many complete waves there are per second

Question 22

what is amplitude

Answer 22

height of the wave from rest(middle) to crest (top)

Question 23

what is the period

Answer 23

the time taken for a complete wave to pass a point

Question 24

wave speed formula

Answer 24

wave speed = frequency x wavelength

Question 25

what do all waves do

Answer 25

transfer energy and information without matter

Question 26

what properties do all electromagnetic waves share

Answer 26

all are transverse

all travel at the same speed in a vacuum

Question 27

in visible light, which colours have the longest/ shortest wavelength

Answer 27

red= longest wavelength, lowest frequency
violet= shortest wavelength, highest frequency

Question 28

what is the law of reflection

Answer 28

angle of incidence= angle of reflection

Question 29

what is a virtual image

Answer 29

an image that cannot be formed on a screen

Question 30

what is refraction

Answer 30

waves changing speed or direction

Question 31

what happens to EM (eg light) waves as they enter a different medium

Answer 31

they are refracted
they travel more slowly in a denser medium
eg when light enters a glass block it goes slower

Question 32

in what direction is the light refracted when it goes in and out of a glass block

Answer 32

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)

Question 33

what happens to sound waves as they enter a different medium

Answer 33

going into denser medium= speed up

opposite to light waves