P5 - Space For Reflection Flashcards
P5 - Space for Reflection
What happens if the distance from a planet is doubled (gravity)?
Gravitational force decreases by a factor of 4 (22)
P5 - Space for Reflection
What is the formula for gravity?
F ∝ 1/d²
P5 - Space for Reflection
What does gravity provide to ensure planets orbit in a circular motion?
A centripetal force - it is directed to the centre of the circle.
P5 - Space for Reflection
What happens if a planet is twice as close (gravity)?
Gravitational force increases by a factor of 4
P5 - Space for Reflection
What is speed?
How fast something’s going
P5 - Space for Reflection
Why is velocity a more useful measure of motion?
Because it describes both the speed and direction
P5 - Space for Reflection
What is a scalar quantity?
A quantity like speed that has only a number
P5 - Space for Reflection
What are some examples of scalar quantities?
Speed Mass Temperature Time Length
P5 - Space for Reflection
What is a vector quantity?
A quantity like velocity that has a direction and a number
P5 - Space for Reflection
What are some examples of vector quantities?
Velocity Force Displacement Acceleration Momentum
P5 - Space for Reflection
What is relative speed?
How fast something is going relative to something else.
P5 - Space for Reflection
What will the relative speed be of a car going the same way as you?
The car will have a small speed relative to your car
P5 - Space for Reflection
What will the relative speed be of a car going the opposite direction to you?
The car will have a bigger speed relative to your car.
P5 - Space for Reflection
What happens to the vectors if two things are moving in the same directions?
The vectors are added
P5 - Space for Reflection
What happens to the vectors if two things are moving in the same directions?
Vectors are subtracted
P5 - Space for Reflection
What is used if an object mov against the current e.g. Across the wind?
Pythagoras theorem. Velocity is needed.
P5 - Space for Reflection
What does u stand for in the equations of motion?
Initial velocity
P5 - Space for Reflection
What does v stand for in the equations of motion?
Final velocity
P5 - Space for Reflection
What does s stand for in the equations of motion?
Distance (or displacement)
P5 - Space for Reflection
What does t stand for in the equations of motion?
Time
P5 - Space for Reflection
What does a stand for in the equations of motion?
Acceleration
P5 - Space for Reflection
What is a projectile?
Something that is projected, or dropped and only has Earth’s gravitational field acting on it.
P5 - Space for Reflection
Give some examples of projectiles…
Golf ball, missile, football.
P5 - Space for Reflection
What is a trajectory?
The path a projectile takes
P5 - Space for Reflection
What shape is a projectile trajectory?
Parabolic
P5 - Space for Reflection
What does the distance a projectile travels depend on?
Angle it is launched at.
P5 - Space for Reflection
At what angle will a projectile travel the furthest?
45 degrees
P5 - Space for Reflection
What happens to the projectile if launched at less than 45 degrees?
Won’t travel as far
P5 - Space for Reflection
What happens to the distance travelled by the projectile if launched at more than 45 degrees?
Projectile will take longer to hit ground and won’t travel as far
P5 - Space for Reflection
How is motion split up?
Into horizontal and vertical
P5 - Space for Reflection
How does gravity affect motion?
Acts downwards - doesn’t affect horizontal at all.
P5 - Space for Reflection
Why does an object launched horizontally accelerate vertically?
Due to gravity. Has no horizontal acceleration (velocity stays same).
P5 - Space for Reflection
How is the resultant velocity calculated?
The vector sum of the separate motions
P5 - Space for Reflection
What happens when an object exerts a force on another object?
It always experiences a force in return.
P5 - Space for Reflection
What is an interaction pair?
When an object exerts a force and experiences one in return
P5 - Space for Reflection
What is Newton’s Third Law of Motion?
If object A exerts a force in object B, then object B exerts an equal and opposite force on object A.
P5 - Space for Reflection
What is the equation for momentum?
Mass x velocity
P5 - Space for Reflection
What are the units for momentum?
Kg m/s
P5 - Space for Reflection
In a collision when no other forces are involved, what happens to momentum?
It is conserved
P5 - Space for Reflection
What does coalesce mean?
Join together (when two objects collide)
P5 - Space for Reflection
What does m1 stand for?
Mass of first object
P5 - Space for Reflection
What does m2 stand for?
Mass of second object
P5 - Space for Reflection
What does u1 stand for?
Velocity of first object
P5 - Space for Reflection
What does u2 stand for?
Velocity of second object
P5 - Space for Reflection
What does v stand for in the momentum equation?
Velocity of combined objects
P5 - Space for Reflection
If the forces are equal how does anything move?
The forces are acting on different objects
P5 - Space for Reflection
What does kinetic theory say that gases consist of?
Very small particles constantly moving in random directions.
P5 - Space for Reflection
How much space do the gas particles take up?
Hardly any - most of gas is empty space.
P5 - Space for Reflection
What do the particles in a gas do with each other?
Constantly collide and bounce off each other (or off the walls).
P5 - Space for Reflection
Why do gas particles exert a force when they collide?
Because gas particles have some mass.
P5 - Space for Reflection
What happens with gas particles in a sealed container?
Gas particles smash against container walls - creates outward pressure.
P5 - Space for Reflection
What happens when the same volume of gas is put in a bigger container?
Larger volume decreases pressure. Fewer collisions between gas particles and walls.
P5 - Space for Reflection
What happens when the volume is reduced in a gas container?
Particles are more squashed - hit walls more often - pressure increase.
P5 - Space for Reflection
What does the pressure of a gas depend on?
How fast the particles are moving and how often they hit the container walls.
P5 - Space for Reflection
What happens if you heat a gas?
Particles move faster and have more kinetic energy. Hit container wall more often, creating more pressure.
P5 - Space for Reflection
What happens if a gas is cooled?
Particles have less kinetic energy - hit walls with less force and less often - pressure reduced.
P5 - Space for Reflection
As well as moving and having a mass, what else do gas particles have?
Momentum
P5 - Space for Reflection
What happens to momentum when gas particles hit the container walls?
Changes velocity and momentum - exerts force on container (pressure).
P5 - Space for Reflection
What is an orbit?
A balance between the forward motion of an object and a force pulling it inwards. (centripetal)
P5 - Space for Reflection
What provides the centripetal force so the planets orbit the Sun in orbits?
Gravitational force between each planet and the sun.
P5 - Space for Reflection
There must be a force acting on it if…
An object is travelling in a circle and constantly changing direction.
P5 - Space for Reflection
Why does the moon orbit the earth?
Because of the centripetal force produced by the gravitational force between Earth and Moon.
P5 - Space for Reflection
What happens to gravity the closer you get to a star or planet?
Stronger force of attraction
P5 - Space for Reflection
What does a stronger force of attraction mean the planets do?
Planets nearer sun move faster and cover orbits quicker.
P5 - Space for Reflection
In addition to planets/stars, what else are held in orbit by gravity?
Moons, artificial satellites and space stations.
P5 - Space for Reflection
What type of orbit do periodic comets have?
Highly elliptical orbits
P5 - Space for Reflection
What happens to comets when they are closer to the sun?
Greater the gravitational force of attraction. Travel much faster here.
P5 - Space for Reflection
What type of orbit do communications satellites need?
Quite high orbit. Above equator. Orbit once every 24hrs.
P5 - Space for Reflection
Whereabouts do communications satellites stay in relation to the earth?
Over same point. Earth rotates with them.
P5 - Space for Reflection
What is the name given to communications satellites?
Geostationary artificial satellites/geosynchronous satellites.
P5 - Space for Reflection
What are geostationary satellites ideal for?
Telephone, TV and radio.
P5 - Space for Reflection
Why are geostationary satellites ideal for TV, radio and telephone?
Stay at same point above Earth and can transfer signals from one side of earth to another in fraction of a second.
P5 - Space for Reflection
Why are geostationary satellites not used for weather and spying satellites?
Too high and too stationary
P5 - Space for Reflection
What kind of orbit do weather and spying satellites need?
Low polar orbit, passing over both poles.
P5 - Space for Reflection
What happens in a low polar orbit?
Satellite sweeps over both poles whilst earth rotates beneath it.
P5 - Space for Reflection
What is the difference for low polar orbit satellites in terms of gravity?
Much closer to earth = pull of gravity stronger and move faster.
P5 - Space for Reflection
How long is the orbit of a low polar orbit satellite?
Often under 2 hours
P5 - Space for Reflection
What happens each time the low polar orbit satellite orbits and what does this allow?
It can scan the next bit of globe and allows whole surface. To be monitored each day.
P5 - Space for Reflection
What wave do communications to and from satellites use?
Microwaves
P5 - Space for Reflection
How are signals for satellite TV and phones transmitted?
From transmitter. Picked up by satellite receiver dish orbiting 1000s of km above Earth. Satellite transmits signal back to earth in different direction and received by satellite dish on ground. OR satellites receiving signal retransmit it to other satellites and eventually back to earth.
P5 - Space for Reflection
What type of frequency do microwaves have?
High frequency - over 3,000MHz (3GHz)
P5 - Space for Reflection
How can microwaves reach distant parts of the planet?
They pass easily through the atmosphere to satellites orbiting Earth.
P5 - Space for Reflection
How is the frequency different for low orbit satellites than those in a geostationary orbit?
Those in low orbit use lower frequencies.
P5 - Space for Reflection
Why do satellite signals weaken?
They travel over long distances (losing intensity and picking up interference).
P5 - Space for Reflection
Why are digital signals used for satellites?
High quality and don’t suffer as much interference.
P5 - Space for Reflection
What is the magnification formula?
image size ÷ object size
P5 - Space for Reflection
What type of lenses do magnifying glasses use to create images?
Convex lenses
P5 - Space for Reflection
Where must the object being magnified be placed?
Closer to the lens than the focal length
P5 - Space for Reflection
What image is produced from a magnifying glass?
Virtual image
P5 - Space for Reflection
What are the stages when photographing an object?
Light from object travels to camera and is refracted by lens, forming an image on the light sensor.
P5 - Space for Reflection
What is the image type when taking a photograph?
Real image - light rays actually meet
P5 - Space for Reflection
What is the image size when taking photos? Why?
Smaller than object because object’s further away than focal length of lens
P5 - Space for Reflection
How does the image appear in a photo?
Inverted (upside down)
P5 - Space for Reflection
Where is an object positioned for a projector?
Object much closer than focal length
P5 - Space for Reflection
What size if the image from a projector?
Larger
P5 - Space for Reflection
How does the object need to be placed when projecting it?
Upside down and very close to lens
P5 - Space for Reflection
What happens to light when an object is projected?
Refracted by lens
P5 - Space for Reflection
What image is produced when an object is projected?
Real, inverted and magnified image on screen
P5 - Space for Reflection
When will an image be in focus?
When the light that forms the image converges on the screen or sensor
P5 - Space for Reflection
How is the image focused in cameras/projectors?
By moving the lens closer to or further from the object
P5 - Space for Reflection
The closer the object to the lens…
The further from the lens the image is formed
P5 - Space for Reflection
If 2 speakers both play the same note at exactly the same time where does constructive interference occur?
When distance travelled by waves from both speakers is either same or different by a WHOLE NUMBER of wavelengths.
P5 - Space for Reflection
If 2 speakers both play the same note at exactly the same time, where does destructive interference occur?
When difference in distance travelled by waves from both speakers is 1/2 wavelength, 1 1/2 wavelength, 2 1/2 wavelength, etc.
P5 - Space for Reflection
What is path difference?
Difference in distance travelled by waves from both speakers
P5 - Space for Reflection
What is a pattern of loud and quiet called?
Interference pattern
P5 - Space for Reflection
What is an interference pattern?
Pattern of constructive (loud) and destructive (quiet) interference. Applies for all type of waves.
P5 - Space for Reflection
What do you need to get a stable interference pattern?
A coherent wave source
P5 - Space for Reflection
What does it mean to have a coherent wave source?
- Waves at same frequency/wavelength
- Waves in phase (troughs and crests line up)
- Waves have same amplitude
P5 - Space for Reflection
What is the coherent source for light?
Monochromatic light (type produces interference patterns)
P5 - Space for Reflection
Why are EM waves with different frequencies used to transmit different types of communication signals?
Thay behave differently in the atmosphere
P5 - Space for Reflection
What happens to signals below 30MHz?
Radiowaves reflected off ionosphere, allowing wave to travel longer distances and deal with Earth’s curvature.
P5 - Space for Reflection
What happens to signals between 30MHz and 30GHz?
Radiowaves and Microwaves pass straight through atmosphere so transmissions must be in line of sight (can’t reflect off atmosphere).
P5 - Space for Reflection
What happens to signals above 30GHz?
Rain and dust in atmosphere absorb and scatter microwaves. This reduces signal strength, so highest frequency that can be used for satellite transmission is about 30GHz.
P5 - Space for Reflection
If 2 speakers both play the same note at exactly the same time, depending on where you stand, what do you hear?
Either loud sound or almost nothing
P5 - Space for Reflection
If 2 speakers both play the same note at exactly the same time what is heard in areas of constructive interference?
Loud sound - waves in phase and amplitude doubles
P5 - Space for Reflection
If 2 speakers both play the same note at exactly the same time what is heard in areas of destructive interference?
Almost no sound - waves exactly out of phase, cancel out.
P5 - Space for Reflection
What happens to all waves as they pass an object or through a narrow gap?
They diffract
P5 - Space for Reflection
What is classed as a ‘narrow gap’?
One which is about the same size as the wavelength.
P5 - Space for Reflection
What achieves the maximum amount of diffraction?
When size of gap = wavelength of wave
P5 - Space for Reflection
Why are long-wave radiowaves great for broadcasting?
Can diffract over hills, through tunnels and over horizon.
P5 - Space for Reflection
How are terrestrial TV and radio signals transmitted?
Using radiowaves (and a dish) and are received by an aerial.
P5 - Space for Reflection
How is a narrow beam produced when transmitting microwaves or radiowaves?
Dishes are many times larger than wavelength so waves don’t diffract much - producing a narrow beam.
P5 - Space for Reflection
What do all waves cause in a medium?
Some kind of disturbance.
P5 - Space for Reflection
What do water waves disturb?
Water particles
P5 - Space for Reflection
What do sound waves disturb?
Air particles
P5 - Space for Reflection
What do EM waves disturb?
Electric and Magnetic fields
P5 - Space for Reflection
What is constructive interference?
Waves disturb in the same direction and reinforce each other.
P5 - Space for Reflection
What is destructive interference?
Waves disturb in opposite directions and cancel each other out.
P5 - Space for Reflection
What is the total amplitude of a wave at any point?
The sum of the displacements (taking into account direction) of the wave at that point.
P5 - Space for Reflection
When do you get interference patterns?
When waves of equal frequency or wavelength overlap.
P5 - Space for Reflection
What happens when a wavefront passes through a gap?
Light from each point along the gap diffracts.
P5 - Space for Reflection
What must a gap be so that light will diffract?
About the same size as the wavelength of light.
P5 - Space for Reflection
What does an interference pattern create?
A bright central fringe, with alternating dark and bright fringes on either side.
P5 - Space for Reflection
What 2 theories were there in the 17th Century to explain the nature of light?
- Particle theory - Isaac Newton
- Wave theory - Christiaan Huygens
P5 - Space for Reflection
What could the particle theory explain?
Reflection and refraction
P5 - Space for Reflection
What could the particle theory not explain?
Diffraction and interference
P5 - Space for Reflection
Why could the particle theory not explain diffraction and interference?
They are both unique to waves
P5 - Space for Reflection
What did Thomas Young’s double slit experiment show?
That light could diffract (through 2 narrow slits) and interfere (to form interference patterns on screen).
P5 - Space for Reflection
What did Thomas Young’s Double Slit experiment involve?
A coherent light source (e.g. laser) shone through two narrow slits.
P5 - Space for Reflection
What is now accepted about light?
It shows properties of a wave (diffraction, interference and polarisation).
P5 - Space for Reflection
What type of wave are EM waves?
Transverse - vibrations at 90º to direction of travel.
P5 - Space for Reflection
How can you make (imitate) a transverse wave?
Shake a rope up and down/side to side, or in a mixture of directions.
P5 - Space for Reflection
What is plane polarisation?
Filtering out all vibrations of waves except a particular direction.
P5 - Space for Reflection
What is ordinary light a mixture of?
Vibrations in different directions
P5 - Space for Reflection
What does passing light through a polarising filter do?
Filter only transmits vibrations in one particular direction.
P5 - Space for Reflection
What is plane polarised light made up of?
Vibrations in one direction only
P5 - Space for Reflection
What happens when light is reflected from some surfaces like water?
It is partly plane polarised
P5 - Space for Reflection
What do polaroid sunglasses act as?
Polarising filters - can filter out reflected glare from sea/snow
P5 - Space for Reflection
What is refraction?
When waves change direction as they enter a different medium
P5 - Space for Reflection
What causes refraction?
Change of speed in waves which causes change in wavelength - NO CHANGE IN FREQ
P5 - Space for Reflection
What happens when a wave passes the boundary between 2 substances?
Changes speed
P5 - Space for Reflection
How does the wave refract if the wave speed decreases?
Wave bends towards normal
P5 - Space for Reflection
How does the wave refract when the wave speed increases?
Wave bends away from the normal.
P5 - Space for Reflection
What does light slow down to when it enters glass?
2/3 normal speed in air (about 2x108m/s rather than 3 x 108m/s)
P5 - Space for Reflection
What is refractive index?
Ratio of speed of light in a vacuum to the speed of light in a medium.
P5 - Space for Reflection
What is the refractive index basically a measure of?
The amount of bending
P5 - Space for Reflection
The higher the refractive index…
The more the light bends when it enters/leaves the medium.
P5 - Space for Reflection
What happens when waves hit a boundary along the normal (exactly 90º)?
No change in direction - change in speed and wavelength