Paper 2 Flashcards
If you hold up an object or lift it at a constant speed, you must be pushing upwards with…
A force that’s the same size as the weight
Hookes law
Force and extension are directly proportional
Hookes law practical
- Add varying masses on a spring to change force
- Measure extension with a ruler at each weight, plot F against E, and to avoid systematic error measure from the first coil rather than the top of the spring
- Find spring constant from the gradient of the graph
Principal of moments
A system is at equilibrium when the sum of clockwise moments = the sum of anticlockwise moments
Gears can be used to increase moments by
Driving a larger gear with a smaller gear
Pressure underwater is due to
The weight of the column of water above an object pushing down on it
Pressure in a gas is due to
Particles colliding with a surface, exerting a force
To increase pressure in a gas
- decrease volume
- add more gas
- increase temperature
Why is there a lower pressure at a higher altitude?
Less dense atmosphere
Typical walking speed
1.5m/s
Typical running speed
3m/s
Typical cycling speed
6m/s
Gradient of a distance/time graph
Velocity
Gradient of a velocity/time graph
Acceleration
Area under a velocity/time graph
Distance
Newton’s 1st
If no resultant force acts on an object, it’s motion is constant
Newton’s 2nd
Force = mass x acceleration
Newton’s 3rd
For every action there is an equal and opposite reaction
Inertia
Tendency for an object to be constant, unless acted on by another force
Newton’s 2nd practical
- Accelerate trolley with mass on string over pulley
- Use photogates to measure acceleration
- Change force by removing masses and placing them on the trolley (to keep total mass the same)
- Ploy F against a, the gradient = the total mass
If person B pushes person A, person A
Also pushes a force on person B
Name 3 effects on thinking distance
Distractions, lack of sleep, alcohol, drugs, speed (proportional)
Name 3 effects on braking distance
Speed, weather, conditions of brake, road, tires
If speed doubles, kinetic energy will
Go up 4x as much
In a collision what is always conserved?
Momentum
Rebound collision
M1U1 + M2U2 = M1V1 + M2V2
Coupling collision
M1U1 + M2U2 = MV
Anything that travels left has a ___ velocity
Negative
Canon balls (idk what it’s called)
0 = M1V1 + M2V2
Longer the time over which momentum is lost or gained
Lower the force exerted
What can be used to increase collision time?
Seat belts, airbags, crumple zones
How do airbags, seat belts and crumple zones reduce force?
They increase collision time, so momentum is lost over a larger time, reducing force
Waves
Transfer energy without transferring matter
Longitudinal waves
Direction of oscillations is parallel to direction of energy transfer
Transverse waves
Direction of oscillations is perpendicular to direction of energy transfer
Frequency
Number of waves passing a point per second
How do sound waves work?
They cause the ear drum to vibrate which sends a signal to the brain
A frequency of over 20kHz is…
An ultrasound
What’s the range of human hearing
20Hz to 20kHz
When sound hits a boundary between mediums, some is __ and some is __
Transmitted, reflected
Are S waves transverse or longitudinal, and can they pass through a liquid?
Transverse, no
Are P waves transverse or longitudinal, and can they pass through a liquid?
Longitudinal, yes
Resulting echoes from sound hitting a boundary can be timed to build up an image of something, for example
Something underwater or a baby scan
Specular reflection
Light reflecting off a smooth surface, where angle of incidence = angle of reflection
Diffuse reflection
Where a rough surface will scatter light
T/F? EM waves can travel through a vacuum
TRUE
Name a use for radio waves
Phones, TV, wifi
Name a use for microwaves
Cooking (absorbed by water)
Name a use for infrared radiation
Cooking (absorbed by surface)
Name a use for visible light
Vision
Name a use for ultraviolet
Sunbeds
Name a use for Xrays
Medical scans
Name a use for gamma rays
Medical
All EM waves are emitted and absorbed by ___, except gamma which is emitted by ____
Electrons, nuclei
Which EM waves are an example of ionising radiation?
Ultraviolet, Xrays, Gamma
As you go from radio– gamma, what changes?
- shorter wavelengths
- higher frequencies
- more energy
Rp- showing matte black to be best absorber and emitter of IR
- Leslie cube with IR thermometer or tubes wrapped in different materials under IR lamp
- shiny materials are worst emitters/absorbers
If speed decreases, how are wavelength and frequency effected?
Wavelength decreases
Frequency remains the same
Refraction
When a wave enters a new medium, so it’s speed changes, causing it to change direction
If a wave slows down, it bends___ the normal, causing the angle of refraction to be ___ than the angle of incidence
Towards, smaller
Principle focus
Where the lens makes rays cross over
Focal lengthv
Distance from centre of lens to principal focus
To see where an image is formed, draw two rays from top of object
- Straight through the centre
- Parallel then through principal focus
Images are either
Real or virtual
Diminished or magnified
Inverted or upright
We perceive different colours when
Different wavelengths of light are absorbed by the retina
Why will objects appear certain colours
They reflect some wavelengths and absorb others
Blackbody
Theoretical object that perfectly absorbs and emits all wavelengths of radiation
If rate of absorption is greater than the rate of emission, how is temperature effected?
Increases, however this then increases rate of emission
Permanent magnets
Always produce a magnetic field
Induced magent
Become magnetised when in another magnetic field
What direction to field lines go
North to south
Which metals are magnetic
Steel iron cobalt nickel
A current carrying wire produces its own
Magnetic field
Motor effect
A current carrying wire in a magnetic field will experience a force
If a wire is parallel to magnetic field lines…
It experiences no force
Fleming’s left hand rule: thumb
Force
Fleming’s left hand rule: index
Magnetic field
Fleming’s left hand rule: middle
Current
How to motors work using the motor effect?
Both sides of a coil experience a force in opposite directions and it turns
To increase speed of a motor
- add more turns to coil
- increase pd/current
- use a stronger magnet
What does a split ring commutator do?
Ensures current is reserved every half turn in order to keep the coil spinning
What direction does current flow?
Positive to negative
How do loudspeakers work?
Using motor effect
- current sent from source, causing coil and speaker cone to vibrate, producing sound waves
Generator effect
A wire that’s moved through a magnetic field will result in an alternating potential difference being induced
In a dynamo, what’s used instead of a split ring commutator?
Slip rings
To increase output in a generator-
More turns in coil, stronger magnet, turn faster
If no slip ring, output is (AC/DC)
AC- graph goes above and below X axis
Why does turning a generator faster require energy?
Induced current produces its own opposing field
How do microphones work?
Generator effect
Sound waves cause coil to oscillate past magnet, inducing a signal
With slip rings, output is (AC/DC)
DC, graph stays above X axis
Step UP transformer
- more turns on secondary coil
- voltage increases
- current decreases
Step DOWN transformer
- more turns on primary coil
- voltage decreases
- current increases
Transformers
Change transmission voltage through the national grid to reduce energy loss as heat due to resistance of cables
How does a transformer work?b
- AC input to a primary coil induces alternating magnetic field in soft iron core
- this induces a current in the secondary coil
- the side with the most turns (N) has the greater p.d. (V) – N and V are directly proportional
Order of stars’ life cycle (red giant)
Nebula, proto star, main sequence star, red giant, white dwarf, black dwarf
Order of stars’ life cycle (super red giant)
Nebula, proto star, main sequence star, super red giant, supernova, neutron star//black hole
Orbits are circular, so while speed is constant…
Velocity is always changing due to direction changing
Centripetal force
Always acts towards the centre of the orbit
Elliptical orbit
Gets faster as it gets closer to earth
Redshift
a result of the space between the Earth and the galaxies expanding. This expansion has the effect of increasing the wavelength of the light from these galaxies, shifting them towards the red end of the spectrum.
Distant galaxies are more redshifted, as they’re
Receeding at a greater rate
What is redshift used as evidence for?
Big band theory
What’s CMBR, and how does it provide evidence for the big bang theory?
Cosmic microwave background radiation- microwave radiation is detected from all over space// could be matter cooling from the big bang theory
Protostar
Gravity pulls the cloud of dust and gas together, leading to a rise in temperature and pressure
Main sequence star
Temperature is high enough for hydrogen fusion to begin and the star lights. Forces of gravity and fusion energy are balanced
Red giant
Hydrogen fusion stops, the star contracts, heats up and helium fusion begins
White dwarf
Stars outer layers drift away, leaving a hot white core
Black dwarf
Star cools until it no longer emits light
Red super giant
Hydrogen fusion stops, the star contracts, heats up and helium fusion begins. The star continues fusing heavier elements up to iron
Supernova
Fusion stops, star collapses under gravity and then explodes. Elements heavier than iron formed
Neutron star
Only the core of the star remains, with a density close to that of the atomic nucleus
Black hole
Star is sufficiently massive, gravity so large not even light can escape
