Flashcards in P5 Deck (40):
How does a satellite stay in orbit above earth?
They are pulled toward Earth by the force of gravity thus they are constantly falling but they also have a velocity at right angle to this fall and thus the resultant force of motion which is in a diagonal direction- this is the centripetal force
This happens at every point in the orbit so it changes direction constantly and accelerated in a circular path around the planet but at the same height
Describe how a geostationary satellite works?
They orbit high above the earth at around 36 000km so lower gravitational force and slower speed and so have an orbital period of 24 hours
They staying above the same position over the earth all the time - orbiting above the equator
It needs centripetal force provided by gravity to move in circular motion
Describe how a low polar satellite works?
It orbits closer to earth (340km) so gravitational force stronger and so has a shorter orbital period- around 90 minutes because it gas FASTER speed
As the Earth rotates, the satellite can observe any part of the planet over a few days
Goes over the poles
What are the uses of geostationary and low polar satellites?
- Geostationary used for TV and mobile phone signals
- used for weather mapping and forecasting
- Low polar creates clearer images because closer
- Needs less powerful communication tech
- Military uses- spying
What equation should you use if the object travels in a straight line and at a constant acceleration?
v = u + at
s = ut + 1/2at2
v2 = u2 + 2as
What is the name of the shape of the trajectory of a projectile?
Describe a projectile's motion in terms of its speed and acceleration
- Its horizontal velocity stays the same throughout because air resistance is ignored and the only force acting on it was the initial kick
- No horizontal acceleration
- Its vertical velocity increases steadily as it falls because gravity accelerates it at a rate of 10m/s2
- Creates a resultant vector- the resultant velocity- the ever increasing downward velocity
- Air resistance would decrease horizontal velocity if considered
What is Newton's third law?
Every action has an equal and opposite reaction
- equal and opposite force is exerted
When a crane holds a load, describe the forces involving this
The load pulls the crane down and crane pull sup with equal and opposite force
The earth attracts the load/crane to the ground and the crane/load attracts the earth to it
What is done to increase the quality of the signal?
Dishes with size much bigger than the wavelength is used
They reflect the signal into the central receiver to be processed by TV
What is a terrestrial signal?
Microwave signals sent from local transmitter
What kind of signal frequencies are used to communicate with nearby satellites?
What kind of signal frequencies are used to communicate with distant satellites?
Why does satellite communication use digital signals?
Because any interference can then be easily removed
Why do long radio waves have a large range?
Because they have a low frequency so they are reflected off the ionosphere and travel out of line of sight
Why do radiowaves diffract better?
Because they have longer wavelengths and the longer the wavelength, the bigger the diffraction
How are interference patterns caused?
They are caused by the waves travelling different distances- called the path difference
What produces constructive interference?
If 2 waves of similar frequencies coincide in phase they will superimpose the wave energy and produce a wave with double the amplitude
The path difference must be an even number of half wavelengths
What produces destructive interference?
If two waves are exactly out of phase they will cause a wave of 0 amplitude
The path difference must be an odd number of half wavelengths
What is AM?
Changing the amplitude of the carrier wave as it changes on the original signal
Who are the 2 scientists involved in the development of the light model?
Sir Isaac Newton
What did Newton say about light?
That it was a particle rather than wave because otherwise it would diffract but in shadows there is a clear edge
It would otherwise spread out but light travels in straight lines
How was Newton's light model proved to be wrong?
Waves were made to diffract using a small slit the same size as the wavelength
It forms an interference pattern as light waves do
It was also polarised showing that It is not only a wave but a transverse wave
What is polarisation?
It only happens in transverse waves
It uses a filter to make the vibrations of the light only move in one plane because there are filters in different directions preventing the light to move this way
It can use a Polaroid filter to do this
What affects the refractive index of a material?
- The more slowly light travels through that material
- The denser the material
....the higher the refractive index
- The shorter the wavelength of the light the slower it travels in the medium thus the greater the refractive index
Materials with a higher refractive index causes the light to ...
...slow down more and bend towards the norm
When light enters a denser medium...
... it slows down, wavelength reduces,
Both speed and wavelength return to normal once it exits the medium`
What are the two conditions needed for total internal reflection?
- It must be in the more optically denser material
- Angle of incidence must be higher than the critical angle
How does refractive index affect critical angle?
The bigger the refractive index, the smaller the critical angle
Give some uses of TIR
Cats' eyes TIR the car's headlight to show where the road markings far ahead of them
Optical fibres to send info/ endoscope
Binoculars and telescopes
The fatter the convex lens...
... the shorter the focal length because it refracts more
Light hitting the lens parallel to the principle axis will...
... refract and go through the principle focus
Light hitting the lens at an angle to the principle axis after diverging from a focus will...
... travel out of the lens a parallel to principle axis
Light passing through the optical centre will...
... continue to travel in the same direction
What kind of images form from a projector?
It will form an inverted image that is real- meaning it will form on a screen when focused
If the object is close to the lens, it will be a larger image
if object is far away, it will form smaller image than size of object
What kind of images do magnifying glasses produce?
It forms a virtual image that is the right way up
What parts of the electromagnetic spectrum cannot pass through the atmosphere?
The higher energy waves such as gamma
What frequency of radio waves are reflected by atmosphere and what pass through?
less than 30MHz be reflected but more than this and it will pass through
How are signals passed between satellites?
As digital signals: pulses of microwaves