physics test waves Flashcards
amplitude
– the distance from the equilibrium position to the maximum displacement
wavelength
the distance between a point on one wave and the corresponding point on the next wave
Frequency
the number of waves that pass a single point per second
Speed
the distance travelled by a wave each second
what is speed related to
frequency and wavelength
What does speed equal
𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 × 𝒘𝒂𝒗𝒆𝒍𝒆𝒏𝒈𝒕𝒉
transverse waves
Has crests and troughs
Vibrations of the particle are at right angles to the direction
of travel of the wave
An example is light
Longitudinal waves
Consists of compressions (particles pushed together) and rarefactions
(particles moved apart)
Vibrations of particles are parallel to the direction of travel
of the wave
An example is sound
what is a wavefront
a surface containing points affected in the same way by a wave at a given time such as crests or troughs.
Reflection
Waves reflect off smooth, plane surfaces rather than
getting absorbed
Angle of incidence = angle of reflection
Rough surfaces scatter the light in all directions, so they
appear matte and unreflective
Frequency, wavelength, and speed are all unchanged
Refraction
The speed of a wave changes when it enters a new medium
If the wave enters a more optically dense medium, its speed
decreases and it bends towards the normal
If the wave enters a less optically dense medium, its speed
increases and it bends away from the normal
In all cases, the frequency stays the same but the wavelength
changes.: speed is proportional to wavelength.
diffraction
Waves spread out when they go around the sides of
an obstacle or through a gap
The narrower the gap or the greater the
wavelength, the more the diffraction
Frequency, wavelength, and speed are all unchanged
What happens when light is reflected of a plane mirror
Upright Same distance from the mirror as the object Same size Virtual A line joining object and image cuts the mirror at right angles.
when can refraction be shown
when light is passed through a glass slab at an angle to its normal
When light enters a more optically dense medium
the angle of incidence is greater than the angle of refraction
The opposite is true when light enters a less optically dense medium.
Angle of incidence
The angle between the incident ray
and the normal
angle of refraction
The angle between the refracted ray and the normal
The refractive index n of a medium is defined as
the ratio between the speed of light
Total internal reflection occurs when
the angle of incidence is greater than the critical angle and the light reflects back into the medium.
the light must also be travelling from a more optically dense medium into a less
optically dense medium (most common example is glass to air).
optical fibre
a long thin rod of glass surrounded by cladding which uses total internal reflection to transfer information by light, even when bent.
converging (convex) lens
A transparent block which brings light rays together at a point
called the principal focus by utilising refraction.
focal length
the distance between the centre of the lens and the principal focus.
when are real images formed
when the distance of the object from the centre of the
lens is greater than the focal length. They are images where light actually
converges to a position and can be projected onto a screen.
When are virtual images formed
When the distance of the object from the centre of
the lens is smaller than the focal length. They are images where light only
appears to have converged and they cannot be projected onto a screen.
How to describe image
The image formed is enlarged/same size/diminished and upright/inverted
where are converging lenses used in
Converging lenses are used in magnifying glasses and binoculars
What happens when white light is passed through a glass prism
When white light is passed through a glass prism, it splits
up into its constituent colours. This happens because the
different colours travel at different speeds in the glass, so
they refract by different amounts.
what are the seven colours in order of decreasing wavelength
The seven colours in order of decreasing wavelength
are red, orange, yellow, green, blue, indigo and violet
(ROYGBIV).
the shorter the wavelength the greater the
refractive index.
Properties of electromagnetic waves
Transverse waves Do not need a medium All electromagnetic waves travel with the same high speed of 3.0 x 108 ms -1 in a vacuum and approximately the same speed in air can be polarised
Typical wavelengths
radio: several metres to several km; • microwaves: 2 - 3 cm; • infra-red: between 780 nm and 1 mm; • visible light: 4 x 10-7 to 7 x 10-7 m; • u.v. : 100-400 nm; • X-rays: ~ 10-8 to 10-11 m; • gamma rays < 10-12 m
The higher the frequency of an EM wave, the greater its ____
energy
Radio waves are used for
radio and television communications. They have a longwavelength
and are reflected by the ionosphere.
Microwaves are used for
satellite communication and in microwave oven. They pass through the
ionosphere and penetrate deep into food.
Infrared radiation is used in
remote controllers and infrared cameras.
Visible light is used in
fibre optics.
Ultraviolet light is used in
medical and dental practices such as killing bacteria, creating
fluorescent effects, curing inks and resins, phototherapy
X-rays are used in
medical imaging and in security as they can penetrate material easily
Gamma radiation is used in
medicine (radiotherapy), industry (sterilization and disinfection) due
to its high energy.
Hazards of electromagnetic waves
Too much exposure to ultraviolet light skin increases the risk of skin cancer.
X-rays and gamma rays are ionising radiation that can cause mutations leading to cancer.
Microwaves can cause internal heating of body tissues.
Infrared radiation can cause skin burns.
Sound waves
Sound waves are longitudinal waves created by vibrating sources.
Sound waves comprise compressions and rarefactions.
The wavelength is the distance from the centre of one compression (or from the centre of one
rarefaction) to the centre of the next compression (or rarefaction).
A medium is needed to transmit sound waves (such as air).
amplitude and frequency of sound waves
The greater the amplitude of a sound wave, the louder it is.
The greater the frequency of a sound wave, the higher its pitch.
Speed of sound in different mediums
The speed of sound in air is 343 ms-1(increases with temperature), the speed of sound in water is 1493 ms-1, and the speed of sound in steel is 5130 ms-1
The range of audible frequencies for a healthy human ear is
20 Hz to 20000 Hz.
Infrasound
Is low-frequency sound waves with a frequency below 20 Hz.
Ultrasound
Is high frequency sound with a frequency greater than 20000 Hz
Where do you measure amplitude from
the middle line
The sine of the critical angle at an air-glass surface is equal to
1/refractive index of glass
A real image of an object projected onto a screen by a converging lens is always ___
inverted
What is the wavelength of microwaves
0.125m
What type of electro magnetic wave does a tv sensor use
infrared
What sit he speed of sound in water
1500 m/s
