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195 Cards in this Set

  • Front
  • Back
How is velocity different to speed?
Velocity is how fast you are going and the direction you are going in
What is velocity measured in?
m/s and diection e.g. degrees
What is displacement?
The distance in a particular direction (with relation to velocity)
How is speed calculated?
speed=distance/time
What are some vector quantities?
velocity and displacement they both have magnitude and direction
How can average speed be calculated using u and v (speed at the start and speed at end)
(u+v)/2 only true for constant acceleration
How can average speed be calculated?
total distance/ total time
On a displacement time graph:What does gradient of line show?
speed
On a distance time graph: What does it mean if line is flat?
Car has stopped
On a distance time graph: What does it mean if the graph is steeper?
The car is going faster
On a distance time graph: What does it mean if the gradient is negative?
The car is going back to starting point
On a distance time graph: What does a steepening curve represent?
acceleration
On a distance time graph: What does a levelling off curve mean?
deceleration
What is acceleration?
how quickly velocity is changing
Can acceleration just be a change in direction?
Yes, it can be a chnage in direction, a change in speed or both
Is acceleration a vector quantity?
yes
Give an equation for acceleration:
acceleration = change in velocity/time taken
What does v-u mean?
Change in velocity as v is final velocity and u is initial velocity. Can also be written as deltav
What is the units for acceleration?
m/s^2
In a velocity time graph:What does the gradient represent?
acceleration
In a velocity time graph: What do flat sections of graph represent?
steady speed
In a velocity time graph: What does it mean if graph is steeper?
greater acceleration or deceleration
In a velocity time graph: What does a negative gradient represent?
deceleration
In a velocity time graph:What does the area under the graph represent?
distance travelled in that time interval
In a velocity time graph: What does a curve represent?
Changing accerleration
When will an object experience an attractive force?
When it is put in the gravitational field of another object
How does gravity affect objects on surface of planet?
It makes things accelaerate to the ground
What is gravitaional fiel strength and what are its units?
acceleration due to gravity, force per unit mass e.g. m/s^2 or N/kg
What gives an object weight?
gravity
What is the gravitational field strength of earth?
10 m/s^2
What is weight caused by?
pull of gravitational force
What are the units for weight and what is it measured with?
Newton, Nspring balance or newton meter
What is the gravitational field strength of the moon?
1.6N/kg
What is the formula to work out weight using g?
Weight (N)=mass (kg) x gravitational field strength (N/kg)
Is weight a force?
Yes, the force of gravity pulling an object to the centre of the earth
How many forces are acting on an object at any given time?
at least two
What is the resultant force?
the overall force on a point or object
When can you find the resultant force jsut by adding/ subtracting forces?
When the forces all act along the same line
What does a resultant force cause in an object?
change in velocity
What happens if the resultant force on a sationary object is 0?
The object will remain stationary
What happens is there is no resultant force on the moving object?
The object carries on at same velocity
What does it mean if there is a NON-zero resultant force?
object will accelerate in direction of the force
What is the equation to calculate resultant force from acceleration and mass?
Resultant force (N)= mass (kg) x acceleration (m/s^2)
What is the equation for newtons 2nd Law?
a=F/m
What is newtons 3rd law?
When two objects interact, the forces they exert on each other are equal and opposite ( a difference in mass means acceleration is different, a=F/m)
What does friction always do to a moving object?
slow it down (and stop)
What is static friction?
Friction between two solid surface that are gripping
What is sliding friction?
Friction between two solid surfaces which are sliding past each other
What is resistance? (friction)
"drag" from gases or liquids
When does resistance increase?
When speed increases
How would you reduce drag?
steamline shape
How does surface area affect drag?
The larger the surface area of an object the greater the drag
What is terminal velocity?
When the resistance force (drag) is equal to the accelerating force (weight or thrust) The forces are balanced
What does terminal velocity depend on?
drag in comparison to weight. Drag depends on surface area and shape
What is the accelerating force on all falling objects?
gravity- they fall at the same rate except for air resistance
What is the total stopping distance?
The time between the driver first spotting the hazard sign and the vehicle coming to complete stop
What is stopping distance a sum of?
thinking distance and braking distance
What affects thinking distance?
how fast you are going, how "dopey" you are
Do bad visability and distractions affect thinking distance?
no, it is just the driver doesn't notice the hazrd until it is closer
What is braking distance affected by?
1. Speed2. How good brakes are3. Mass of vehicle4. How good tyres are- minimum tread depth of 1.6mm to account for water5. How good grip is a)road surface, b) weather conditions, c) tyres
What is the equation for Momentum?
Momentum (kgm/s)=Mass(kg) x Velocity (m/s)
Is momentum a vector quantity?
yes
When does Momentum Before=Momentum after?
momentum is conserved when no external forces act
What does force equal with respect to momentum?
Force (N)= Change in momentum (kgm/s)/time (s)
What does a larger force mean?
fast change of momentum and greater acceleration
Why do seat belts help in a car crash?
The change in momentum stays the same, however the time it takes for the change to occur is greater, so resulatnt force is smaller
What is work done?
When a force moves an object, energy transferred is the work done
What is the equation to calculate work done?
work done= force x distance moved in direction of force
What is the unit for work done?
joules- it is energy transferred
When considering work done does it matter if the energy is used usefully?
o it is just the energy transferredn
How can power be worked out using work done?
average power= work done/ time taken
What is power?
rate of energy transferred
What is equation for power?
P=E/t
What is the unit for power?
watt (W) 1W= 1J/s
What is equation for kinetic energy?
KE=1/2 x massx speed^21/2mv^2
If you double the speed what happens to KE?
KE quadruples as KE=1/2mv^2
What does kinetic energy depend on?
mass and speed
To stop a car what does KE have to be converted into?
heat energy at the brakes and tyres
What is the equation linking KE transferred and work done by brakes?
kinetic enrgy transferred equals work done by brakes1/2mv^2=Fx dWhere F= maximum braking forced= braking distance
If you go twice as fast what has to happen to the braking distance?
Must increase by factor of four to convert extra KE. F can't be increased as it is maximum braking force
What happens to braking distance if you double the mass?
doubles
What is the equation for gravitational potential energy?
GPE=massx gx height
Why does an object have GPE?
because of its vertical position in a gravitational field
How does an object gain GPE?
When it is lifted vertically work is done against force of gravity
What happens to GPE when an object falls?
It is converted to KE.(some is actually lost to friction and disappated as heat or sound)
What happens when you apply brakes to a car?
work is done, brakes reduce KE of car by transferring it into heat and sound
How do Anti-Locking Brakes help drivers stay in control of car?
automatically pump on and off to stop wheels locking and preventing skidding
How do regenerative brakes work?
They put the cars motor into reverse and it acts as an electric generator converting electricity into chemical energy stored in baterry. It doesnt waste energy as energy isnt lost to heat and sound
What does it mean if a car is more powerful?
It tranfers more energy from fuel every second
When cars reach their top speed what does the driving force equal?
resistive force
Why are cars built to be aerodynamic?
This reduces air resistance meaning a greater top speed can be reached with the same driving force
When does an object become charged?
When negatively charged electrons are added to or removed from it.
What happens when two electrically charged objects are brought together?
If two objects have the same charge, they will repel and if they have opposite charges, they will attract each other.
Why do plastic charged objects lose their charge against a metal object?
Electrical charges can move easily through metals.
What is it called when electrical charges move through a metal or other electrical conductors?
An electrical current-measure of how much charge flows every second.
What is the equation for working out the current?
I:Current in Amps(A)= Q: Charge in coulombs(C) divided by t= Time in seconds(s).
What is the potential difference?
The work done between two points in a circuit per coulomb of charge passing through the circuit.
What is the equation to work out potential difference?
V:p.d. in volts(V)= W: Work done in joules(J) divided by Q: Electrical charge in coulombs(C)
What is a switch?
Turns the current in a circuit off and on.
What is the cell and battery?
Creates a p.d. across a circuit. A battery is two or more cells.
What is a diode?
Allows current to flow one way but not the other.
What is a resistor?
Helps regulate current flow in a circuit.
What is a fuse?
Breaks current flow if current gets too large.
What is a voltmeter?
Measures p.d.
What is an ammeter?
Measures current.
What is a thermistor?
A temperature-dependent resistor.
What is a LDR?
A light-dependent resistor.
What affects current flow?
The amount of p.d. and the resistance of the components.
What is Ohm's law?
V:Potential difference in volts(V)=I:Current in amps(A) multiplied by R:Resistance in ohms
How can you plot a graph of potential difference against current?
By measuring the current flow at a range of p.d. values.
What happens when a material obeys Ohm's law?
The current through it is directly proportional to the p.d. applied to it if the temperature of the material is held constant.
How can you find the resistance of any component in a circuit?
By measuring the current flow through it and the p.d. across it. Resistance= p.d. divided by current
How can thermistors be used?
It can be used to activate a switch for e.g. central heating because as it gets warmer the resistance of the thermistor gets lower.
How can LDR's be used?
They can be used in circuits that turn on automatically at night because the brighter the light the lower the LDR's resistance and vice versa.
What are non-ohmic devices?
Devices that don't follow Ohm's law, current and p.d. are not proportional to each other.
What is an example of a non-ohmic device?
A filament bulb- the current that flows through the filament, will make it hotter and that increases the resistance of the filament, so it's more difficult for the current to flow.
Why does the resistance change in a filament bulb?
The current is carried by electrons and they 'do work'. Therefore, the electrical energy is transferred through heating the filament.It makes the filament vibrate and get hotter, making it harder to make electrons to pass through-resistance increased
How are current values recorded negative?
By changing the power supply round so the current flow the opposite way.
Why does diodes not work the same both ways?
It only works like a one-way valve for electricity- allows current to pass in one direction but not the other.
When is the resistance of a diode low and high?
Low-In its forward direction. High-In the reverse direction.
What is the most efficient lighting?
LED's- lasts hundered of times longer than filament, used in torches and some car lights.
What is in a series circuit?
Only one route for electric current to flow along; there are no branches or splits.
What happens if all cells in a series circuit are facing the same way?
The total p.d. is all the individual cell p.d.s added together.
What happens if the circuit in a series circuit is broken?
The current stops everywhere because the current in a series circuit is the same everywhere.
What happens when the resistance in a circuit is large?
The current flow will be smaller.
How do you find the total resistance in a circuit?
You add together the values of the resistors.
How do you calculate the current from the total resistance and the p.d. of the battery?
I:Current(Amps) = V:p.d. divided by R:Total resistance
What happens to the total p.d. in a series circuit?
It's shared between the components.
How do you work out the p.d. across each resistor?
(Total p.d. multiplied by Resistance of Resistor) divided by Total Resistance
What does a parallel circuit contain?
At least one place where the current splits into two or more separate currents.
What happens to the p.d. in a parallel circuit?
The p.d. is the same across each component while the current is different in different parts of the circuit.
What happens to the current in a parallel circuit?
The current sets off from the cell and then splits in half when it comes to a fork in the circuit. Half the current flow through the top resistor and half through the bottom one. When they pass, they join up and form a big current again.
What happens when the current splits?
The two smaller currents always add up to the larger one. When the join again, the current will be the same as before.
How can you determine how the current splits?
Through the resistance of each branch- The larger the resistance, the smaller the current that flow down it.
What does changing the flow in one branch of a parallel circuit affect?
It has no effect on the other branch(es) but it does affect the main current flow.
What happens when bulbs are put in parallel?
The p.d. is the same across the branches but the resistance is greater because there might be more bulbs on one branch so the current is reduced.
What is direct current(d.c.)?
When the current flows in one direction only from positive to negative.
What is the advantage of d.c.?
Low-voltage electronic circuits can use it, so electronic devices can be portable.
What is alternating current(a.c.)?
When the direction of the current changes many times per second.
What is the frequency of the electrical supply in the U.K.?
50 Hertz.
What is an advantage of a.c.?
Can be easily changed using transformers, over long distances the voltage is increase to reduce energy loss.
What is a disadvantage of a.c.?
Many electrical appliances run on d.c., if it's run on the mains, the a.c. supply has to be changed into d.c.
What does a cathode ray oscilloscope do?
It measures the voltage of an electrical supply.
Why do appliances use the mains?
A cell would not be powerful enough for some appliances, the supply is continuous and it can recharge batteries.
What is the structure of an electric cable?
Stranded copper wire. Coloured inner insulation. Outer insulation.
Explain the properties of the stranded copper wire in electrical cables?
This is the core of the cable. Copper is a very good electrical conductor. The bundle of thin copper strands can be bent and coiled without breaking.
Explain the properties of the coloured inner insulation in electrical cables?
The colour indicates which wire is which and insulates the copper from other wires within the cable.
Explain the properties of the outer insulation in electrical cables?
This is stiffer and harder than the inner insulation. It provides strength and extra protection.
What are plugs made out of?
The body is made from tough insulating plastic to protect the user from any electrical contacts. Connecting pins made from a conducting metal are designed to fit into holes in an electrical socket.
What are the three connecting pins that most modern plugs have?
Live and neutral pins which connect to complete the electrical circuit and an earth pin.
How should a plug be wired?
The live wire(brown) is connected to fuse which in turn is connected to the live pin. The neutral wire(blue) and is connected to the neutral pin. The earth wire(green and yellow) is connected to the earth pin.
What are the rules when wiring a plug?
Check the correct colour is attached. Assure the wires aren't stretched. Assure the screws grip the wire firmly. No copper wire should be visible.The cable grip should hold the outer insulation firmly.The fuse should match the appliance power rating.
What type of cable should an appliance need?
It depends on the power and its type of insulation.
What can a faulty electrical appliance cause?
It might reduce the resistance of the circuit, so a larger current than normal might flow. Then it can catch fire. It can cause an electrical wire to touch a metal part which can cause an electric shock.
What are the safety devices used to protect against faulty electrical appliances?
Fuse, earth wires and circuit breakers.
What does a fuse do?
It breaks the electrical connection if the current gets above the fuse rating which is the maximum current it can hold. It contains a length of wire that melts if the current in a circuit gets too high.
What does an earth wire do?
It's a low-resistance path for electric current to flow through, it's connected to the metal parts of an appliance. If there's a fault, then a large current flows along the earth wire, causing the fuse to blow and makes it safe.
What if appliances have a plastic casing?
They don't need an earth wire because there are no metal parts that can become electrified. This is double-insulated, it uses a two-core cable as it doesn't need an earth wire.
What does a circuit breaker do?
They're similar to fuses but they're more sensitive and operate faster.
What does a residual current circuit breaker do(RCCBs)?
It works by sensing any difference in current between the live and neutral wires. In a normal circuit the current in both wires are the same. But if RCCB senses a difference, it disconnects the electricity(used in lawnmowers).
What is the equation for measuring the power of a device(measuring how much energy it transfers per second)?
P:Power in watts(W)= E:Energy in joules(J) divided by t:Time in seconds(s).
What is the equation for measuring the power of a device(measuring the current and the potential difference)?
P:Power in watts(W)= I:Current in amps(A) multiplied by V:Potential difference in volts(V).
What is the equation for calculating the amount of charge flowing in a given time?
Q:Charge in coulombs(C)= I:Current in amps multiplied by t:Time in seconds(s).
What does p.d. measure?
It's a measure of the 'electrical push'. As electrons move, they transfer energy and the harder they're pushed, the more energy is transferred.
What does the amount of energy transferred by one coulomb of charge depend on?
It depends on the p.d. that pushes it.
How do you calculate energy transferred?
E:Energy transferred in joules= V:p.d. in volts(V) multiplied by Q:Charge in coulombs(C).
What is the most common fuel in fusion?
Hydrogen- fusion involves lighter elements.
What are the two heavier isotopes of hydrogen?
Deuterium- One neutron in the nucleus.Tritium- Two neutrons in the nucleus.
What happens when the hydrogen isotopes are pushed hard together?
The nuclei fuse together to form the heavier element helium.
How is energy released in nuclear fusion?
When the two isotopes are pushed together, a vast amount of energy is released which also leaves one neutron after.
How is forcing nuclei together possible in stars?
It's due to the very high temperatures that make atoms move extremely fast and collide with high energy. And the great mass of a star means it will have a strong gravitational field. It squashes the high-energy hydrogen atoms together.
What is a nebula?
Large clouds of dust and gas(mainly hydrogen) which comes together due to gravity. All stars start as a nebula.
What is a protostar?
It's made when the temperature and pressure in a nebula increases until hydrogen can fuse. It's all done under the influence of gravity which overcomes electrostatic repulsion. So, a protostar is born.
What is a main sequence star?
The hydrogen fusion is in full flow. The star will be brighter and hotter than a protostar. The gravitational force and pressure of radiation is equal so it doesn't grow or shrink.
What is a red giant star?
When hydrogen runs out, it starts to fuse heavier elements which releases more energy. Therefore, the pressure of radiation becomes bigger than the gravitational force. So, the star starts to expand and push out.
What is a white dwarf?
Once the star has lost all of its fuel, it will lose all of its outer layers. This exposes the core which is extremely hot.
What is a black dwarf?
This is created when the white dwarf has cooled down and it stops glowing white. It doesn't emit any radiation.
What is red super giant star?
After the main sequence, it starts to fuse heavier elements. It then has more fuel, so there's a bigger pressure of radiation. Therefore, it starts to expand and release more energy.
What is supernova?
Once heavy stars run out of fuel, it starts to collapse within itself. It repeats this until it reaches a critical point. This causes a massive shock-wave called a supernova. It causes the outer layers to collapse. The shock-wave lasts a few seconds but releases a vast amount of energy. It becomes as bright as 10 billion stars.
What is a neutron star?
The star's core is exposed which is just neutrons. The resulting star is very dense.
What is a black hole?
This occurs in a very rare case. The core continues to collapse within itself until a singularity point. It collapses until an infinitely small point where not even light can escape it.
What is the cycle of a sun-like star?
Nebula-Protostar-Main Sequence Star-Red Giant Star-White Dwarf-Black Dwarf
What is the cycle of a massive star?
Nebula-Protostar-Main Sequence Star- Red Super Giant Star-Supernova-EITHER: Neutron Star OR Black Hole.
What do radioactive elements have?
An unstable nucleus.
How do atoms give off radiation?
Through radioactive decay which leads to a stable element.
What is background radiation?
Constant, low-level radiation around at all times.
What are sources of background radiation?
ElementsCosmic RadiationAtomic Bomb Tests (Man-made)Largest Source: Radon Gas
What type of radiation is ionising?
All of them.
How much do alpha particles ionise?
It ionises thousands of air molecules as it travels, slowing down as it does.
How much do beta particles ionise?
It ionises a few atoms before it loses energy.
How much do gamma rays ionise?
It ionises one atom or molecule each.
Why are alpha and beta particles deflected in different amounts?
An alpha particle has over 7000 times as much mass which means it's more difficult to deflect.
What was the conclusion of Rutherford's alpha-particle scattering?
Most of the atom is empty space and nearly all the mass is in a tiny, positively charged lump at the centre.
Why is radon gas dangerous?
It emits alpha particles which are dangerous to get inside your body once you breath it in.
How is radon gas produced?
It's produced by the radioactive decay of uranium and radium which are found in rocks. As they decay into radon, the gas seeps up from the ground. It becomes a problem when radon gas can collect inside houses and buildings.