Download OCR Physics P5 - Wey Valley School

OCR Physics Module P5 SPACE FOR REFLECTION
P5a Satellites, gravity and circular motion
Satellite
a satellite is an object that orbits a larger object in space
Orbit
gravitational force keeps a satellite in orbit
Gravity
universal force of attraction between masses; decreases as the masses get further apart
Circular motion
circular motion requires a centripetal force and that gravity provides the centripetal force for orbital motion
Circular motion – acceleration
artificial satellites are continually accelerating towards the Earth due to the Earth’s gravitational pull, but their
tangential [“straight line”] motion keeps them moving in an approximately circular orbit
Orbital period
time taken for a satellite to make one complete orbit
Orbit of Moon/Earth
the Moon remains in orbit around the Earth and the Earth in orbit around the Sun due to gravitational forces
between them
Orbit of planets
the orbit period of a planet depends upon its distance from the sun; orbit is not circular but is a slight ellipse
Orbit of comets
the variation in speed of a periodic comet during its orbit around the sun is caused by its highly elliptical orbit
Gravity
universal force of attraction between masses; decreases as the masses get further apart
Orbit height
the orbit of an artificial satellite depends on its height above the Earth’s surface
Satellite orbit
orbital period of an artificial satellite increases with height above the Earth’s surface; satellites in lower orbits
travel faster because the gravitational force is stronger
Satellite use
height of orbit of an artificial satellite determines its use
Geostationary orbiting satellite
high orbit; slower orbit speed; orbits the Earth once in 24 hours around the equator; orbits over ‘fixed point’ on
Earth’s surface (Communications; Weather forecasting; GPS)
Polar orbiting satellite
low orbit; faster orbit speed; orbits the Earth in a few hours over the Poles; covers more area as it orbits the
rotating Earth; (Imaging the Earth’s surface; Military uses [‘Spy satellites])
P5b Vectors and equations of motion
Scalar quantity
Vector quantity
Parallel vectors
Vectors at right angles
Speed
Velocity
Equations of motion
Use equations
direction is not important – e.g. speed, mass
direction is important – e.g. velocity, force
calculate the resultant vector by adding the individual components together
calculate the resultant vector by right angle triangle rule [Pythagoras] – H2 = (A2 +O2)
scalar quantity; measures how fast an object is moving; s=d/t
vector quantity; speed + distance
suvat; s= distance (!); u = start speed; v = final speed; a = acceleration: t = time
v = u + at;
s = (u + v) t
v2 = u2 +2as;
s = ut + ½ at2
2
P5c Projectile motion
Projectiles
Trajectory
Object moving horizontally
Horizontal projection
Equations (P5b)
Vectors
Resultant velocity
Forces
Downward acceleration
Horizontal acceleration
P5d Momentum
Momentum
Momentum – equation
Action/reaction
Collisions
Collisions – forces
Force – equation
Acceleration and injuries
Acceleration and force
Safety features in cars
Changing momentum
Conservation of momentum
Events
Momentum of collisions
P5e Satellite Communication
EM spectrum – communication
Microwaves
Earth’s atmosphere
Effect of ionosphere
Effect of particles
Radio waves
Radio/TV reception
Diffraction
Diffraction – maximum
Long wave radio waves
FM radio
when fired in the air; missiles, cannon balls, golf balls, netballs, darts and long-jumpers
path of a projectile; path of an object projected horizontally in the Earth’s gravitational field is curved – parabolic
has two components of velocity – horizontal and vertical (ignore air resistance)
an object projected horizontally in the Earth’s gravitational field, (ignore air resistance): has a constant horizontal
velocity; is accelerating towards the ground so has a steadily increasing vertical velocity
use suvat equations for calculations for an object projected horizontally above the Earth’s surface where the
gravitational field is still uniform
the horizontal and vertical velocities of a projectile are vectors
the resultant velocity of a projectile is the vector sum of the horizontal and vertical velocities
ignoring air resistance, the only force acting on a ball during the flight is gravity
projectiles have a downward acceleration and that this only affects the vertical velocity
for a projectile there is no acceleration in the horizontal direction (ignore air resistance)
the greater the mass of an object and/or the greater velocity, the more momentum the object has in that
direction
momentum = mass x velocity
every action has an equal and opposite reaction
ball struck by an object in sport (e.g. cricket ball and bat) is an example of a collision
when an object collides with another object, the two objects exert an equal and opposite force on each other
Force = change in momentum ÷ time
injuries in vehicle collision and many sporting injuries are due to a very rapid acceleration of parts of the body
a rapid acceleration causes a rapid change in momentum and so a large force is exerted
crumple zones; seatbelts; airbags; work by increasing the time for change in momentum
spreading the change in momentum over a longer time: reduces the forces required to act; reduces the injury
momentum is a property that is always conserved; total momentum is the same before and after the event
such as collisions; explosions; recoil; rocket propulsion
total momentum the same before and after a collision two objects moving in the same direction (including
calculations of mass, speed or momentum)
em waves used to transmit information – microwaves; radio waves
information transmitted using microwaves to orbiting artificial satellites and then retransmitted back to Earth;
microwaves are sent as a thin beam because they only diffract by a small amount due to their short wavelength
stops some radio frequencies; allows others to pass through; reflects others
radio frequencies below 30MHz are reflected by the ionosphere
above 30GHz, rain, dust and other atmospheric effects reduce the strength of the signal due to absorption and
scattering
radio waves have a very long wavelength
aerial for radio/terrestrial TV; ‘dish’ for satellite TV
waves can ‘spread out’ as they pass an object or pass through a gap; amount of diffraction depends upon the
size of the gap and the wavelength of the wave
maximum diffraction occurs when the wavelength equals the size of the gap
long wave radio waves have a very long range because they diffract around hills and over the horizon
shorter range; only to ‘horizon’
AM
FM
P5f Nature of waves
Interference of waves
Constructive interference
Destructive interference
Interference – results
Constructive interference
Destructive interference
Light – as waves
Light – diffraction patterns
Polarisation
Polaroid
P5g Refraction of waves
Medium
Refraction
Normal
Change in wave speed
Change in wavelength
Change in direction
Refractive index
Refractive index – equation
Snell’s law
Reflection
Air to glass
Dispersion
Refraction and critical angle
Total internal reflection (TIR)
TIR and refractive index
Media and critical angle
Critical angle – equation
P5h Optics
Convex lens
Focal length
‘Fat’ lenses
Convex lenses uses
Real image
Ray diagrams
Focussing – camera
Focussing – projector
Virtual images
Magnification formula
medium wave and long wave radio waves are AM (amplitude modulation); signal transmitted on a carrier wave
that has the signal superimposed on it; information transmitted as variation in amplitude of the wave
higher frequency waves; higher ‘quality’ signal but shorter range; information transmitted as variation in the
frequency of the wave
an effect resulting from two waves that overlap
areas where the waves add together; patterns of reinforcement
areas where the waves subtract from each other; patterns of cancellation
louder and quieter areas in sound; bright and dark areas in light
number of half wavelengths in the path difference for two waves from the same source is an even number
number of half wavelengths in the path difference for two waves from the same source is an odd number
diffraction of light and its associated interference patterns are evidence for the wave nature of light
stripes of light and dark; explained by interference
electromagnetic waves are transverse waves and so can be plane polarised – vibrations in one plane
block ‘glare’ from water etc by polarising light being reflected from the surface into one plane
a substance that light passes through
change in direction of a wave due to the wave passing from one medium into another
reference line at 90˚ to the point the wave enters the medium; angles measured from the normal line
refraction occurs at the boundary between two mediums due to a change in the wave speed
change in speed causes a change in wavelength and may cause a change in direction
as a wave enters a denser medium, the wave speed decreases and the wave bends towards the normal
refractive index is limited to the amount of bending after a boundary; more dense medium has higher refractive
index
refractive index = speed of light in vacuum ÷ speed of light in medium
refractive index (n) = sin i ÷ sin r; i = angle of incidence; r = angle of refraction
some, or all, of a light ray can be reflected when travelling from glass, or water, to air
a ray of light travelling from air into glass the angle of incidence is usually greater than the angle of refraction
when white light is refracted into the spectrum colours; blue light is deviated more than red light
refraction occurs when a ray of light hits a glass/air boundary at an angle less than the critical angle
TIR happens when a ray of light hits a glass/air boundary at an angle greater than the critical angle
TIR can only occur when a ray of light travels from a medium with a higher refractive index into a medium with a
lower refractive index and the angle of incidence is greater than the critical angle
different media have different critical angles because of having different refractive index; the higher the refractive
index of a medium the lower is its critical angle
Sin c = nr ÷ ni ; c = critical angle; ni = refractive index of ‘incident’ medium; nr = refractive index of ‘refraction’
medium
() shape; converging lens; converge parallel rays of light onto a single point (focal point/focus)
of a convex lens as being measured from the centre of the lens to focal point (focus)
have short focal lengths
magnifying glass; cameras; projectors
projectors and cameras produce real images on a screen/film; image can be projected; image inverted (upside
down)
find the position and size of the real image formed by a convex lens by drawing suitable ray diagrams
images produced by cameras are focussed by moving the lens closer to /further from the film/sensors
images produced by cameras and projectors are focussed by moving the lens closer/further to the object
cannot be projected onto a screen but are the right way up
magnification = image size ÷ object size