Additional Science: Physics (II) Flashcards
What is the equation for working out speed?
What is the equation for working out acceleration?
What is the equation for working out weight?
What is the equation for working out force?
What is the equation for working out work done?
What is the equation for working out momentum?
What do the parts of the distance-time graph tell you about movement?
a-b = moving
b-c = stopped
c-d = moving quicker (than at a-b as line is steeper)
What do the parts of the velocity-time graph tell you about movement?
a-b = accelerating quickly
b-c = steady speed
c-d = decelerating
d-e = stopped (steady speed)
e-f = accelerating quickly
f-g = steady speed
g-h = decelerating
How can you work out the distance traveled from a velocity-time graph?
Work out the area beneath the graph
When are the forces of an object balanced?
When it is still or travelling at a steady speed
What do unbalanced forces do to the movement of an object?
It will cause the object to speed up / slow down
What is the force of gravity on Earth?
10N/kg (9.8N/kg)
What is the equation for working out power?
Power (P) = work done (or energy transferred) (E) ÷ time take (s)
What is the equation for working out gravitational potential energy?
Gravitational potential energy (Ep) = mass (kg) x gravity (N/kg) x height (m)
How is work done to an elastic object stored?
Via elastic potential energy (shape is changed)
What is Hooke’s law?
Extension of an elastic object is directly proportional to force
Force (N) = spring constant (k) x extension (m)
F = k x e
How would you draw out an example of Hooke’s law in practice?
What happens to extension of an object if the force becomes too great?
The directly proportional extension of the object in relation to the force stops…
When stopping a car what can affect the thinking time?
Drugs and alcohol
Distractions
Tiredness
When stopping a car what can affect the breaking distance?
Speed
Mass of vehicle
Tyres
Brakes
Road surface
Weather
Why do falling objects reach terminal velocity?
The weight remains constant with gravity causing the object to accelerate
Air resistance is small to begin with, but as the object speeds up it increases
Eventually the air resistance will equal the weight (as this does not change)
Once the forces are balanced there can be no change in speed – terminal velocity
What is resultant force and when is the resultant force on an object zero?
The overall force in one direction – this is zero when the object is stationary
What can be described as a fluid?
What happens to the frictional forces as an object accelerates through a solid
Gases and liquids
Frictional forces increase as the speed increases, but eventually reach terminal velocity
What is momentum and what affects it?
Momentum is how quickly each kg of the object is moving – objects with great momentum are harder to stop
Momentum is affected by mass and velocity
What is the equation for working out kinetic energy?
Kinetic energy (J) = ½ mass (kg) x speed2 (m/s)
Ek = ½ mv2
Friction usually causes what type of energy to be lost?
Heat (thermal) energy
All objects with elastic potential energy are all able to do what?
Return to their original shape
During a collision or explosion between objects, what happens to the momentum?
The momentum in a collision or explosion is conserved
What safety features do you find in cars to help reduce the affect of momentum during a crash?
Cars are designed to convert kinetic energy safely in a crash via: -
Seatbelts
Crumple zones
Air bags
Side impact bars
In a car crash safety features are designed to what?
Increase the time taken to slow the passenger(s) down
How are static charges produced?
Rubbing an object to remove electrons (negative charges)
Objects which gain electrons become negatively charged
Objects which lose electrons become positively charged
When objects collect a static charge, which type of charge moves?
Negative charges only (the electrons can be moved, but the protons are held in the nucleus (not moving))
How does a photocopier use static charges?
Drum of the photocopier has positive charge
When light falls onto the drum it loses its charge – light shines through white bits, so only the black bits of the paper to copy remain charged
Ink is negatively charged so it is attracted to the positive parts of the drum
This is transferred to the paper
How does a smoke precipitator use static charges?
Dust and ash pass through a negatively charged grid and pick up a negative charge
Dust is then attracted to positively charged plates which are shaken and removed at intervals
How can spray-painting use static?
Paint is positively charged – these paint particles repel each other to create a fine mist
Objects being sprayed are negatively charged so the paint is attracted to it
When can static electricity be dangerous?
Static can be dangerous when flammable gases / liquids are used which a spark could ignite
E.g. petrol stations or operating theatres
How can the dangers of static electricity be reduced?
The dangers can be reduced by ‘earthing’ objects to prevent sparks from forming
What happens when 2 like charges are put together?
What happens when 2 opposite charges are put together?
Like charges repel
Opposite charges attract
What is an earth cable and what is it used for?
Earth cables must be good conductors (e.g. copper) to provide the electrons with an easy route to the ground
Why can a build-up in static charges cause a spark?
If the charge on an isolated object is great enough there may be a large enough potential difference between the object and the ground to spark (electrons jump the gap)
What are the symbols for the following: -
Switch
Cell
Battery
What are the symbols for the following: -
LDR
Diode
Resistor
What are the symbols for the following: -
Fuse
Lamp
Variable resistor
What are the symbols for the following: -
Voltmeter
Ammeter
Thermistor
What component does this current/voltage graph represent?
A resistor at a constant temperature
What component does this current/voltage graph represent?
A filament lamp
What component does this current/voltage graph represent?
A diode
What is the equation for working out potential difference?
Potential difference (V) = current (A) x resistance (Ω)
What is the equation for working out resistance?
Resistance (Ω) = potential difference (V) ÷ current (A)
Explain the shape of the voltage / current graph for a filament lamp
As the voltage is increased the current increases
As the voltage is increased the filament gets hot, exciting the particles making it harder for the electrons to flow through (therefore reducing the current increase)
Why does an increase in temperature reduce the current?
The heat excites the metal particles vibrating them more – this makes it harder for the electrons to flow through, therefore reducing the current
What is a diode and how does current flow through it?
A diode is a component which only allows energy to flow through in one direction
What is a LDR, how does current flow through it and where may it be used?
LDR (light dependent resistors) are affected by light – the resistance decreases as the light increases
These are useful for streetlights
What is a thermistor, how does current flow through it and where may it be used?
Thermistors are resistors which are affected by temperature – the resistance decreases as the temperature increases (this can be used in fridges)
How does resistance affect the current?
The higher the resistance the lower the current
How can you work out the total resistance in a circuit?
To work out the resistance in a circuit add up the resistance of all the individual components
What are the rules for current in a series circuit?
Series circuit – current is the same
What are the rules for the potential difference in a series circuit?
Series circuit – voltage is shared between components (adds up to the total voltage of the battery)
What are the rules for current in a parallel circuit?
Parallel circuit – current is shared between the different branches
What are the rules for potential difference in a parallel circuit?
Parallel circuit – voltage is the same in each branch (the same as the battery)
Label the wires of a plug, including their colours
Blue = neutral; brown = live; green / yellow stripes = earth
What is the difference between a.c. and d.c. supplies?
a. c. (alternating current) – current is constantly changing direction
d. c. (direct current) – current does not change direction
What is the frequency and potential difference of the mains supply in the UK
50Hz and 230V
What is an electrical cable made from?
Why is each material used?
Copper for the wire (good electrical conductor) and plastics for the cover (good insulator)
What is the purpose of a fuse, and how does it work?
A fuse is designed to increase the safety of an electrical appliance – if too much electricity flows through the plug the wire melts, breaking the circuit (turning the appliance off)
Why are appliances with a metal case usually ‘earthed’
If the earth wire touches the side of the metal case someone using the appliance could get an electric shock as the electrons flow through them to the Earth
Earth wire provides an easier route for the electrons, preventing electrocution
What happens to the potential difference in the live wire with respect to the neutral wire?
The live terminal of the mains supply alternates between +ve and –ve with respect to the neutral terminal
What happens to the potential in the neutral terminal with respect to the earth?
The neutral terminal stays at a potential close to zero with respect to earth
How should the size of fuse in a plug be determined?
The fuse should allow a slightly higher current than the appliance demands
What is electrical current?
The flow of electrons around a circuit
When a charge flows through a resistor, what form of energy is the electrical energy transformed in to?
Heat (thermal) energy
What 2 equations can be used for working out power?
Power (W) = energy transformed (J) ÷ time (s)
Power (W) = current (A) x potential difference (V)
What is the equation for working out the energy transformed in a circuit?
Energy (J) = potential difference (V) x charge (C)
What is the equation for working out charge?
Charge (C) = current (A) x time (s)
What units are these measured in?
Power
Resistance
Charge
Power = watts
Resistance = ohms
Charge = coulombs
What experiment was carried out by Rutherford and Marsden – what was it used to show?
Rutherford and Marsden’s scattering experiment – an alpha particle (helium nuclei) was fired at a thin sheet of gold (1 atom thick)
They found that some travelled through, some were deflected at different angles and some were reflected back
They used this experiment to establish the modern model of the atomic structure (+ve nucleus with –ve electrons orbiting)
What are the relative charges and masses on these parts of an atom?
Proton
Neutron
Electron
Proton = +ve (mass of 1)
Neutron = neutral (mass of 1)
Electron = -ve (mass of 1/2000th)
Why does an atom have no overall charge?
It has the same amount of protons (+ve) and electrons (-ve), which cancel each other out
What is used to prevent electrical overloads?
Earthing, fuses and RCCBs (residual current circuit breakers which detect a difference in current quickly cutting off the power by opening a switch)
What is potential difference?
The work done per unit charge (energy transferred in Joules per coulomb of charge passing between two points)
Potential difference = work done ÷ charge
V = W ÷ Q
What are the 3 types of radiation?
Alpha
Beta
Gamma
What can happen when radiation is absorbed by a substance?
Radiation may make things hotter, or set up an alternating current with the same frequency as the radiation itself
Why are some atoms radioactive?
Some atoms have unstable nuclei which give out radiation all the time, no matter what is done to them
What are these types of radiation made from: -
Alpha radiation
Beta radiation
Gamma radiation
Alpha: helium nucleus (2 protons and 2 neutrons)
Beta: high energy electron
Gamma: an electromagnetic wave
What is an ion, how are they created?
Give an example
An atom with a charge – created when atoms pick up electrons (become negative) or lose electrons (become positive)
E.g. Cl- and Na+
What part of an atom is always the same for a particular element?
Proton number
What part of an atom is always different for different atoms?
Proton number
What is an isotope?
An atom of the same element with a different amount of neutrons
What do these numbers represent in the atom?
Atomic number
Relative atomic
Atomic number – number of protons (usually the same as the number of electrons)
Relative atomic mass – number of protons and neutrons
What effect does alpha decay have on the nucleus of an atom?
Alpha decay is the loss of a helium nuclei (2 protons + 2 neutrons)
This means that the proton number decreases by 2 (element changes) and the mass decreases by 4
Draw and label and atom
What is an isotope?
An atom with a different number of neutrons
How are the 3 types of radiation affected by electric and magnetic fields?
Alpha & beta are deflected by electric and magnetic fields – gamma is not affected
What does half-life mean?
Are all half-lives the same?
Half-life is the time it takes for a radioactive material to break down to half its original radioactivity – this can occur in seconds, or over millions of years
Which of the 3 types of radiation is the most ionising and why?
Alpha is the most ionising because it is the biggest – causing the most damage to the atoms
Which is the most penetrative type of radiation?
What can each type of radiation be stopped by?
Gamma is the most penetrative radiation
Alpha: stopped by paper
Beta: stopped by aluminum foil
Gamma: stopped by thick lead (or meters of concrete)
Which is the most dangerous type of radiation outside of the body? Explain…
Gamma – it can penetrate to the fragile internal organs
Which is the most dangerous type of radiation inside of the body? Explain…
Alpha – it is the most ionising radiation, causing most damage to the cells
How can radioactive substances such as Tahllium be used for medical ‘tracers’?
Tracers use gamma radiation so it is less dangerous to the patient (they also have a short half life, so they are not radioactive for long)
How are the 3 types of radiation affected by electric and magnetic fields?
Alpha & beta are deflected by electric and magnetic fields – gamma is not affected
Main sequence stars, depending upon size, can develop into what after their hydrogen runs out?
Red giants > white dwarfs
Or
Red super giants > supernova (and leaving neutron stars / black holes)
Draw the life cycle of a star
What effect does beta decay have on the nucleus of an atom?
When beta radiation is emitted a neutron turns to a proton – this means the proton number increases by 1 and the element changes
What is background radiation and where does it come from?
Background radiation is the radiation around us all the time – this may come from space, rocks under-ground, X-rays etc…
What is a chain reaction and how does it occur?
When atoms split they release neutrons – these neutrons can go on to split other atoms, which also release neutrons (a chain reaction)
Draw and label a diagram to show how a chain reaction may occur
What are the two most common substances used in nuclear reactors?
Uranium 235
Plutonium 239
What is nuclear fission?
Nuclear fission is when a nucleus splits into 2 smaller nuclei and 2/3 neutrons are released (+ energy)
What must happen for nuclear fission to occur?
A neutron must be absorbed
What happens to an atom when they undergo nuclear fission?
The nucleus splits and releases 2/3 neutrons
What is nuclear fusion and where does it happen?
2 atomic nuclei join together to create a large one (this is the process by which energy is released in stars)
Where does nuclear fusion happen?
Stars – hydrogen fuses to helium
