physics Flashcards
what is a transverse wave?
they oscillate perpendicular
they don’t require a medium to travel
examples include em waves and light
what is a longitudinal wave?
they oscillate parallel
they don’t require a medium to travel through
examples include sound seismic p-waves
whats the equation for wave speed
frequency x wavelength
what em wave has the lowest energy?
radio
what em wave has a higher energy?
gamma rays
what em wave has the lowest frequency?
radio
what em wave has the highest frequency?
gamma
what em wave has the smallest wavelength?
gamma
what em wave has the largest frequency?
radio
what is a use for radio waves?
tv signals
what is a use of microwaves ?
reheating food and mobile phone connections
what is a use for infrared?
heating and optical fibre communication
what is a use for visible light?
seeing
what is a use for uv light?
tanning and detecting forged bank notes
what is a use for x-rays?
medical images
what is a use for gamma rays ?
killing cancer cells
what are the applications of em waves?
satellite communication, mobile phones, infrared, bluetooth and wifi
what is satellite communication?
refers to any communication link that involves the use of an artificial satellite in its propagation path.
what kind of signals does satellite communication use?
high power signals over long distances, concentrated by a dish antenna
what kind of wave is used by satellite communication?
1-40 GHz microwaves
how do mobile phones work with em waves?
A mobile phone receives microwave signals from a nearby phone mast (or ‘transmitter’) and sends microwave signals back.
what kind of signal does a mobile phone use?
High power networked system, range of several km.
what kind of wave is used by a mobile phone?
800 MHz to 2.6 GHz microwave borderline
whats the difference between 2G 3G 4G 5G?
these offer increasing speeds for data. high frequencies have a greater data capacity but travel less distance 9in the air and penetrate into buildings less
what is infrared?
this is a wireless mobile technology used for device communication over shorter ranges
what kind of signal does infrared use?
Low power device to device links, range only a few meters
what kind of em wave does infrared use?
IR wavelength 870 nm or 930-950 nm.
what is one application of infrared
Used for remote controls and for data transfer between computers, phones etc. Requires lines of sight.
what is bluetooth?
a wireless technology that allows the exchange of data between different devices
what kind of signal does bluetooth use?
Low power device to device links, range up to about 10 m.
what kind of em wave does bluetooth use?
2.4 to 2.4835 GHz borderline of microwave and radio waves
what is wifi?
Wi-Fi is the wireless technology used to connect computers, tablets, smartphones and other devices to the internet.
what kind of signal does wifi use?
Medium power networked system, range ~ 10-100m
what kind of em waves does wifi use?
2.4 to 2.4835 GHz borderline of microwave and radio waves
what is phase difference?
When two waves have the same frequency and wavelength, the phase difference tells us the difference in phase angle between the waves.
what happens if two waves are in antiphase?
they will have a phase difference of 180 degrees meaning that the peaks will overlap with the throughs
what is a coherent wave?
Coherent waves have a constant phase difference with one another. Waves can only be coherent if they have the same wavelength or frequency.
when does destructive interference?
Destructive interference will take place when the peaks of one wave line up with the troughs of the other wave.
when will constructive interference occur?
Constructive interference will take place when the peaks of one wave line up with the peaks of the other wave.
constructive interference =
n λ
destructive interference
ⁿ⁄₂ λ
what is diffraction?
Diffraction changes the direction of a wave and causes it to spread. Diffraction occurs when a wave:
passes an edge
passes through a narrow gap
goes past an object
whats changed during diffraction?
direction in which the wave is going
when does maximum diffraction occur?
when the wavelength of the gap is equal to the gap
a gap much larger than the wavelength causes …..
little spreading and a sharp shadow
a gap similar to the wavelength causes ….
a lot of spreading with no sharp shadow
