Physics IGCSE Flashcards
To help revise for the Edexcel Certificate in Physics
What are the units of gravitational field strength?
N/kg or m/s^2
average speed =
speed = distance/time
How do you determine the displacement from a velocity-time graph?
Area under the curve
What are the effects of a force?
change in velocity over time (acceleration); change in shape
What is friction?
A force which opposes motion
Describe the forces acting on falling objects and describe how they reach terminal velocity
The object initially accelerates toward the Earth due to the gravitational force. As the object’s velocity increases, so too does its air resistance. Eventually, the force of air resistance = gravitational force, so the forces will be balanced. According to Newton’s 1st Law, unless acted on by a force, an object will travel at constant velocity
Stopping distance =
s.d. = thinking distance + braking distance
What factors affect thinking distance?
Metal condition of driver; tiredness; influence of drugs; alcohol; medication; level of concentration
What factors affect braking distance?
speed; road conditions; tyre conditions; car mass; brake conditions
What is the centre of gravity?
the point within something at which gravity can be considered to act
Moment =
Moment = Force x Perpendicular distance
What is Hooke’s Law?
The extension of an elastic material is proportional to the force applied until the material reaches its elastic limit
What is an elastic material?
A material which will retain its original shape after a force which has been deforming it has been removed
What celestial body do comets orbit?
The Sun
How do planets orbit the Sun?
In nearly circular orbits
Describe the orbit of a comet
Comets have very elliptical, elongated orbits. They travel much faster when moving near to the Sun, because the gravitational force is much stronger (the force is inversely proportional to the square of the distance from the centre of gravity)
orbital speed =
o.s. = 2πr/T
What is the universe?
Collection of billions of galaxies
What is the Milky Way galaxy?
Our galaxy; a collection of billions of stars
What is the solar system?
Collection of all the celestial bodies (planets, natural satellites, comets, asteroids etc.) which orbit the Sun
What is current measured in?
Amperes (Amps)
What is charge measured in?
Coulombs
What is energy measured in?
Joules
What is resistance measured in?
Ohms
What is potential difference measured in?
Volts
What is power measured in?
Watts
What does current in a resistor cause?
Transfer of electrical energy to heat energy and an increase in temperature (e.g. in a kettle’s element)
Power =
P=IV
Energy =
E=IVt
Is mains electricity AC or DC?
Alternating Current
What does current depend on in a series circuit?
Voltage of cell
Does current vary in a series circuit after passing through components?
NO
What is the relationship between current, resistance and voltage?
V=IR
What is the relationship between current, resistance and power?
P=I^2R
What is the proportionality between current and resistance?
They are inversely proportional to one another
Voltage =
V=E/Q=P/I=IR
What is current?
The rate of flow of charge
Charge =
Q=It
What is a transverse wave?
A wave whose oscillations are perpendicular to to the direction of the wave’s propagation
What is a longitudinal wave?
A wave whose oscillations are parallel to the direction of the wave’s propagation
Name an example of a transverse wave
Water wave; light wave; EM radiation
Name an example of a longitudinal wave
Sound waves
Define amplitude
The maximum displacement of a wave from its rest (undisturbed) position
Define frequency
The number of oscillations per second
Define wavelength (λ)
The distance (in metres) between the same points in an oscillation and the next (e.g. between two crests)
Define the period of a wave
The time taken for one oscillation
What do waves do?
Transfer energy and information without transferring matter
wave speed =
v=fλ
List all of the waves in the electromagnetic spectrum
Radio waves; Microwave; Infra red; Visible light; Ultra-violet; X-Rays; γ-Rays
What are uses of radio waves?
Broadcasting; communication
What are uses of microwaves?
Cooking food and satellite transmissions
What are uses of infra red waves?
Heating and night vision equipment
What are uses of visible light?
Optical fibres and photography
What are uses of ultra violet rays?
Fluorescent lamps
What are uses of X-Rays?
Internal imaging; medical scans
What are uses of γ-Rays?
Sterilising food and medical equipment
What are dangers of microwaves?
Internal heating of cells
What are dangers of infra red waves?
Burning skin
What are dangers of UV rays?
Blinding; damage to surface cells
What are dangers of γ-Rays?
Cancer; mutations
What type of waves are EM rays?
Transverse waves
What is the law of reflection?
angle of incidence = angle of reflection
Refractive index =
n = sin i/sin r
What is total internal reflection (TIR)
When all of the light from an incident ray is reflected back inside the original medium; when the angle of INCIDENCE is GREATER than the CRITICAL angle; when a light ray moves from an optically denser to less dense material
What is the critical angle?
The angle of incidence where the angle of refraction = 90°; the angle of incidence at which all light is totally internally reflected
sin C
sin C = 1/n
What type of waves are sound waves?
Longitudinal
What is the human frequency for hearing?
20 Hz to 20 kHz (20000 Hz)
What is the unit for power?
Watts
List the different forms of energy
Kinetic, gravitational potential, elastic potential, nuclear, chemical, heat (thermal), sound, light, electrical
What is conduction?
The transfer of thermal energy through a substance without the substance itself moving; caused by the spreading vibration of particles in the substance
What is convection?
The transfer of thermal energy through a fluid by the rising of less dense, hotter fluid, and falling of the denser, cooler fluid.
What is radiation?
The transfer of heat by infra red radiation
Work done =
W = F x d
What is work done equivalent to?
Transfer of energy
GPE =
GPE = mgh
KE =
KE = 1/2mv^2
GPE at top =
KE at bottom
Power is rate of…
energy transfer (work done)
Power =
P=W/t
Describe the energy transfers involved in generating electricity from wind energy
The kinetic energy from the wind spins the turbines, which drive generators which convert the kinetic energy into electrical energy
Describe the energy transfers involved in generating electrical energy from geothermal energy
heat energy -> kinetic energy -> electrical energy
Describe the energy transfers involved in generating electricity using solar heating system
heat -> electrical
Describe the energy transfers involved in generating electricity from solar cells
light -> electrical
Describe energy transfers in obtaining electricity from fossil fuels
chemical energy -> heat energy -> kinetic energy -> electrical energy
Describe energy transfers in obtaining electricity from nuclear reactions
nuclear energy -> heat energy -> kinetic energy -> electrical energy
Density =
ρ = m/V
Pressure =
P = F/A
How does pressure act on a single point in a fluid which is at rest?
Equally in all directions
ΔP =
ΔP = ρgh
What is Brownian motion?
The random motion of particles in all directions caused by collisions with particles surrounding them.
How do molecules in a gas move?
Randomly; Brownian motion; exerting force (and therefore pressure) on the insides of a container
What is absolute zero?
0K; -273°C; The temperature at which no heat energy is transfered; all atoms stop moving
What does an increase in temperature do to the speed of gas molecules?
It makes them move faster; increases speed
What is the relationship between pressure and temperature (in K) for a gas in a sealed container?
P1/T1 = P2/T2 ; pressure is directly proportional to temperature
What is the relationship between pressure and volume?
P1V1 = P2V2 ; pressure and volume are inversely proportional to each other
What do magnetic field lines represent?
Direction and intensity of a magnetic field
What does electric current in a conductor induce?
A magnetic field in the anticlockwise direction around the wire
What happens when a wire carries a current in a magnetic field?
A force is exerted
What increases the force on a wire carrying a current in a magnetic field?
strength of magnetic field; current
what is induced in a solenoid when it moves through a magnetic field?
a voltage
Which is the most penetrating form of radiation?
γ-radiation
How can you detect ionising radiation?
Using a Geiger-Muller detector (counter)
Name three sources of background radiation
rocks, the Sun, cosmic microwave background radiation
What is activity measured in?
Bequerels (Bq = 1/s)
What is a “half-life”?
The time taken for half of the atoms of a radioactive substance to decay
What are the dangers of ionising radiation
Mutations; cancer; disposal issues
What are α and β radiation, and how much can they penetrate respectively?
α: Helium nucleus with a 2+ charge and a RAM of 4. Stopped by thin card. Cannot travel very fast because it is easily stopped by air particles.
β is an electron with a 1- charge and a RAM of 0. Stopped by 1-2mm of aluminium foil. Can travel relatively fast.
How can you reduce heat loss by conduction?
Use a vacuum; conduction needs a medium to work.
Use air as an insulator (although if the airspace is too large, heat will be transferred by convection)
How can you reduce heat loss by convection?
Use a vacuum; convection needs a fluid to work in.
Use trapped gas or liquids which restrict motion of convection currents.
How can you reduce heat loss by radiation?
Use shiny surfaces which will reflect the IR rays away. Shiny surfaces are also poor radiators of heat; black-bodies absorb and radiate the most heat.
Describe how a simple electric motor works
A single coil of wire is in a magnetic field. A current passes through the wire which makes it move to and fro between 180°. A split ring commutator ensures that the current continues to change direction (otherwise the coil wouldn’t spin)
How can you make a DC motor spin faster?
Increase number of turns on the coil; Increase number of cells in battery; increase the strength of the magnetic field.
Describe Fleming’s left hand rule
If you make a left-hand gesture where the thumb, index finger and middle finger are all orthogonal to one another (perpendicular), if the index finger is the direction of the magnetic field (North to South), and the middle finger is the direction of the current, the thumb will be pointing in the direction of the force exerted on the wire.
Describe the right hand grip rule
If you make a fist with the thumb pointing upwards with your right hand, if the thumb is the direction of the current, the fingers will be pointing in the direction of the magnetic field produced surrounding the wire.
How does a generator work?
A conducting coil moves in a changing magnetic field induces a voltage; since the coil in which the voltage is being induced will be spinning, the electrical connections are made by the carbon brushes which slide over the commutator rings.
State the transformer equation
Vp/Vs = Np/Ns = Is/Ip
What does a step down transformer do?
It decreases the voltage and increases the current.
What does a step up transformer do?
It increases the voltage and decreases the current.
Why might step up transformers be used when transporting electricity across the country in the national grid?
Because using a step up transformer, the current will decrease, and power lost = I^2R, so the current needs to be as low as possible to minimise power lost.
What does a moderator do in a nuclear power plant?
It absorbs fast neutrons, so that they can be readily absorbed into U-235 nuclei sustaining the chain reaction.
What is the role of the control rods?
The control rods absorb neutrons and take them completely out of action. The rods can be raised out of the reactor to increase the rate of the chain reaction, or lowered to completely stop the chain reaction.
Describe the Geiger-Marsden experiment
An α source was surrounded with a lead block with a small aperture to focus a “beam” of α-particles towards a gold leaf. A zinc sulfide screen was used as an α-particle detector (it fluoresced when α-particles struck it). Most particles passed through the screen, but a few of them were deflected (to different degrees).
What three factors influenced the amount of deflection?
- Speed; the faster the particles were deflected through smaller angles.
- Nuclear charge; more highly charged nuclei (i.e. Au-79) caused greater deflections.
- How close the α-particles got to the nucleus; the electric force diminishes with the square of the distance.
What were Rutherford’s deductions?
Atoms must have a very small, dense, charged nucleus at the centre, and be mainly empty space. The experiment showed that the nucleus was one ten-thousandth the diameter of the atom.
What is a fissile material?
An unstable material; ready to split/decay
How can you make experiments more accurate?
- Read off from horizontal/vertical to avoid parallax
- Measure mass of any masses being used (e.g. in Hooke’s law experiments) with a scale
- Use a ruler marked in mm instead of one marked in cm
- Attach any ruler to a clamp stand/ use a set square to make sure that it is vertical/horizontal
- Set all instrumentation to 0; check for 0-error
- Make the results as close to the real (truth) answer as possible
How can you make experiments more reliable?
- REPEAT THEM!
- Get other people to repeat them
- When analysing the data, remove anomalies from mean
What is validity of an experiment?
Whether the experiment is correctly answering the question which it is supposed to answer. This involves careful selection of dependent/independent/control variables.
How can you make an experiment more precise?
By using equipment which reproduces the same results (i.e. reliable equipment)
Describe how a photocopier works.
A statically charged drum is exposed to light, reflected from the document to be copied, which discharges the drum everywhere except where the the dark print does not reflect the light. The charged parts of the drum attract the toner which is then bonded (by heat) to the paper.
Describe how static electricity can be used in an inkjet printer.
The ink droplets are charged and are allowed to be directed to particular places on the paper by deflecting them between charged plates.
Describe how static electricity can be used in paint spraying.
The droplets of paint are given a static charge and the object to be painted is given the opposite charge. Therefore, the paint droplets will be attracted to the surface of the object and they will be evenly spread out from each other - this minimises paint used.
