waves Flashcards

1
Q

what is a longitudinal wave

A

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

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2
Q

what is a transverse wave

A

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

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3
Q

explain the dopler effect

A

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)

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4
Q

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

A

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

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5
Q

describe the role of total internal reflection in prisms

A

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

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6
Q

relationship between refractive index and angle of incidence and refraction

A

n =sin i/sin r

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7
Q

relationship between refractive index and critical angle

A

n= 1/sinc

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8
Q

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

A

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

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9
Q

use of radio waves

A

communications + broadcasting

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10
Q

use of microwaves

A

cooking + satellite transmissions

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11
Q

use of infrared

A

heaters+ night vision

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12
Q

use of visible light

A

optical fibres, photography

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13
Q

use of UV light

A

fluorescent lamps

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14
Q

use of Xray

A

observing internal structure of objects

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15
Q

use of gamma rays

A

sterilising food and equipment; cancer treatment

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16
Q

dangers of microwaves and infrared

A

micro: internal heating of body tissue
infrared: skin burns

17
Q

dangers of ultraviolet waves

A

damage to surface cells and blindness

18
Q

dangers of gamma rays

A

cancer, mutation and simple protective measures against risks

19
Q

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

A
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;
20
Q

what is wavelength

A

distance between two peaks

21
Q

what is frequency

A

how many complete waves there are per second

22
Q

what is amplitude

A

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

23
Q

what is the period

A

the time taken for a complete wave to pass a point

24
Q

wave speed formula

A

wave speed = frequency x wavelength

25
what do all waves do
transfer energy and information without matter
26
what properties do all electromagnetic waves share
all are transverse | all travel at the same speed in a vacuum
27
in visible light, which colours have the longest/ shortest wavelength
``` red= longest wavelength, lowest frequency violet= shortest wavelength, highest frequency ```
28
what is the law of reflection
angle of incidence= angle of reflection
29
what is a virtual image
an image that cannot be formed on a screen
30
what is refraction
waves changing speed or direction
31
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
32
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)
33
what happens to sound waves as they enter a different medium
going into denser medium= speed up | opposite to light waves