Paper 2 Overview Flashcards
SP8a - What is work done?
The energy transferred by a force as it moves an object in the direction of a force.
SP8a - What is the equation for work done?
E = F x d
(Energy = Force x distance moved)
SP8a - What is the equation for Power?
P = E ÷ t
(Power = Energy ÷ time)
SP8a - What is the unit for power?
W - Watts
(Equivalent to J/s - Joules per second)
SP9a - What do you call forces between objects that are touching?
Contact forces
SP9a - What is the name for the regular upward force form the ground when you’re standing?
Normal contact force
SP9a - What are the three non-contact forces?
- Gravitational fields
- Static electricity
- Magnetism
SP9a - What do all objects that produce a non-contact forces have?
A force field.
An area around an object in which another object could experience a force.
SP9a - Describe how the gravitational pull between the earth and the moon are action-reaction forces.
- Force is a vector quantity.
- The force of the moon on the earth is the same size as the earth on the moon but they are in opposite directions.
- Neither objects move in the direction of the force.
SP9c - What is the formula for a moment?
Moment (N m)
=
Force (N) x distance perpendicular to the pivot (m)
SP9c - What could you say when weights around a pivot are balanced?
It is in equilibrium
SP9c - What is the principle of moments?
The some of clockwise moments = the sum of anti-clockwise moments
[When a system is in equilibrium]
SP9b - How do you work out the direction and size of the resultant force using the component forces?
The Parallelogram method:
- (If the start of a diagram hasn’t already been provided, draw to the two forces using a scale)
- Draw another pair of dashed-lines parallel to the forces
- This should form a parallelogram
- Draw a line from the object to the vertically opposite corner
- Measure this line and use the scale to work out the size
- If required, measure the angle to show the direction
SP9b - How do you resolve the component forces using the resultant force?
The Rectangle method:
- Draw faint horizontal and vertical lines fom the object
- Measure the angle from the horizontal/vertical that the object is at
- Using a scale, draw a line the represent this force
- Draw lines down and across from where this line ends to the horizontal and vertical respectively
- Measure out the length from the object to each of these poitns
- Use the scale to work out the size
SP9c - Explain why using two different sized gears in a car may be beneficial.
- The first smaller gear can be connected to the motor where it recieves the moment
- This passes on an equal force to the second larger gear
- Since the second gear is larger, it will have a larger radius.
- This means that its the distance from the pivot will be greate
- Therefore it will have a larger moment (turnign force) as M = F x d
SP9c - Why is a longer lever more effective?
- The formula for a moment (the turning force) is M = F x d
- Thus, by increasing the distance form the pivot, you will either:
- Increase the turning force
- Decrease the force required to produce the same turning force
SP10a - Describe the structure of an atom including features of the sub-atomic particles.
- Proton and neutron in the nucelus, each with a relative mass of 1.
- Protons have a charge of +1.
- Electrons orbit in energy levels each with a charge of -1 and a relative mass of 1/1835 (negligible)
SP10a - Descirbe what a potential difference is.
The force that pushes the electrons to flow around the circuit.
SP10a - What is conventional current?
What we refer to as the direciton of current from positive to negative. Opposite to the flow of electrons.
SP10a - What are the two types of circuits?
- Series: everything connected in one route
- Parallel: many options for different routes.
SP10a - Why may parallel circuits be more beneficial?
- If the circuit becomes incomplete along one path, the rest of the circuit can still continue to function. (e.g - Switches can be connected to different parts meaning lights in parallel to each other can be switched in and off individually)
- If a bulb goes off, the rest of the circuit in parallel to this can still continue to function
SP10b - What is the unit for current and how can it be measured?
Amps (Amperes). Measured using an ammeter which is attached in series to the circuit
SP10b - What is the unit for potential difference and how can it be measured?
Volts. Measured using a voltmeter which is attached in parallel to the component you are measuring the potential difference of.
SP10b - How does total current differ in parallel and series circuits?
- S: The total current is the same at all points throughout the circuit
- P: The total current gets split between the branches of the circuit, inversely proportionate to the resistance of the components in those branches.
SP10b - How does potential difference differ in parallel and series circuits?
- S: The p.d is different across different components, directly proportionate to the resistance of that component
- P: The p.d is tha same at all points across the circuit
SP10c - What is current?
- The flow of electrons
- The rate of flow of charge
SP10c - What is the unit for charge?
C - Coulombs
SP10c - What is the equation linking charge and current?
Q = I x t
(Charge = Current x time)
SP10c - What equation links energy and charge and how can this be changed to link energy to current?
E = Q x V (Energy = Charge x p.d)
since Q = I x t, this means that
E = I x t x V (Energy = Current x time x p.d)
SP10d - What is Ohm’s law?
V = I x R
(p.d (V) = Current (A) x Resistance (Ω))
SP10d - What is resistance?
The force pushing back against p.d opposing and reducing the current.
SP10d - How do you calculate the resistance in series and parallel circuits?
- Series: Add up the resistance of all the components
- Parallel: 1/RT = 1/R1 + 1/R2 + ………..
SP10d - What is key to remember about the size of the total resistance in series and parallel and series circuits?
- S: It is greater than any of the individual resistances
- P: It is smaller than all of the individual resistances
SP10e - What does a IV graph for fixed resistor look like and why?
- It is a straight diagonal line showing direct proportion.
- This is because resistors are ohmic conductors.
- The voltage is directly proportionate to the current.
SP10e - What is an ohmic conductor?
A component in a circuit that follows Ohm’s rule of V=IxR
SP10e - What does the gradient of an IV graph represent?
The inverse of the resistance (1/R)
SP10e - What does a IV graph for diode look like and why?
- A line that is nearly on the x-axis till it shoots up.
- This is because a diode has an infinitely high resistance till a point where it has an infinitely low resistance
SP10e - What does a IV graph for filament lamp look like and why?
- An S shaped ‘curve’.
- This is because the resistance of a lamp increases due to the temperature increase as it conducts electricity at a higher voltage
SP10e - Describe what a graph for resistance of a thermistor would look like and why.
- The x-axis would be temperature (°C) and the y-axis would be resistance (Ω)
- As the temperature increases, the resistance decreases. This forms a negative curve in an L shape
- This can be used to reduce the current in lower temperatures.
SP10e - Describe what a graph for resistance of an LDR (Light-dependant resistor) would look like and why.
- The x-axis would be light intensity (lux) and the y-axis would be resistance (Ω)
- As the light intensity increases, the resistance decreases. This forms a negative curve in an L shape
- This is used for lit up signs outside. In darker conditions (lower light intensity) bulbs don’t need to be as bright.
- Thus, the resistance is higher to reduce the current and brightness
- Resistance is high against the dark side #Starwars
SP10e CP - Describe your set-up for an experiment to compare the relationship of V=IxR in a resistor, and a filament lamp in parallel/series.
- Set up a series circuit with a power pack, an ammeter, a fixed resistor and a voltmeter in parallel to this.
- Provide different voltages from the power pack.
- For each voltage provided, note down the current - Replace the fixed resistor with a lamp and repeat
- Set up the circuit from here so that there is a voltmeter attached in parallel to this.
- Attach another lamp to the circuit with another voltmeter in parallel to this
- Measure out the voltages and currents when different voltages are supplied
- Move one of the bulbs with its voltmeter to a new branch forming a parallel circuit
- Add an ammeter to each branch of the circuit
- Now measure the voltage and current depending on the voltage provided
SP10f - What is the heating effect?
- The heating effect is when a circuit warms up due to the resistance in its wires.
- Work is done against the resistance and so energy is transferred.
- This is in the form of heating and dissipates into the surroundings
SP10f - Where is the heating effect useful?
- In appliances such as electric heaters and kettles where the aim is to use thermal energy, the heating effect is incredibly useful.
- In these circuits, resistance tends to be high.
SP10f - Describe what resistance is in terms of a metal’s structure.
- Current is the flow of electrons.
- A metal is made of electrons flowing around positive metal ions
- When the electrons are moving in the circuit, they can collide into these posistive metal ions.
- These collisions are resistance and they transfer energy
SP10f - How can resistance be reduced in a circuit?
- Choosing a metal with a lower resistance
- Using a thicker wire (more space for electrons to flow)
- Using a shorter wire (less distance in which they can collide)
SP10f - What formula links energy, time and voltage?
E = I x t x V
Energy = Current x time x Voltage
SP10g - What are the four formulae for power?
- P = E/t
- P = I x V
- P = I² x R
- P = V² ÷ R
SP10g - How do you form the the equations that link Power and Resistance?
- We know that P = I x V and that V = I x R
- If we substitue the V in the first equation we get P = I x I x R or P = I² x R
- If we rearrange V = I x R we get I = V ÷ R
- So if we substitute this in we get P = V x V ÷ I or P = V² ÷ R
SP10h - What the voltage and frequency of and type of electricity that comes through mains supply?
- 230V
- 50Hz (changes diretion 50 times per second)
- a.c
SP10h - What are the differences between d.c and a.c?
d.c:
- Only one direction (positive to negative)
- Electrons loose energy as they travel from negative to positive
- A graph showing the direction will only ever be on one side of the x-axis
a.c:
- Constantly switching direction (this is their frequency)
- Electrons vibrate and pass on energy
- A graph showing direction will contantly cross zero and over the x-axis
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SP10i - Describe the five features of a 3-pin plug.
- Live wire: Connects the appliance to the generators at the power station providing 230V
- Neutral wire: The return path to the power station and will be at 0V if circuit is correctly connected
- Earth wire: Connects the metal parts of the appliance to a large spike of metal that pushes down and connects to the ground. Will be at 0V unless the circuit is incorrectly connected
- Fuse: A Safety device usually 3, 5 or 13 A
- Plastic casing: This electrical insulator allows you to safely hold the plug
SP10i - How does an earth wire make an appliance safer?
- If a wire comes loose and touches the metal part of the appliance, the electricity will beable to flow through this.
- When a person touches it, the electricity can pass through the person to the ground.
- This would give them an electric shock.
- However the earth wire provides an easier way to travel to the ground.
- As electrcity always takes the past of least resistance, it goes this way and the person doesn’t get an electric shock
SP10i - How does a fuse provide safety? (Describe this though it’s structure)
- A fuse is a glass tubing with a thin metal wiring that the electricity passes through.
- A faulty appliance may draw too much current which would heat up and cause a fire.
- However depending on the value of the fuse, it will melt once the current has reached a certain level and cause the circuit to be incomplete meaning current stops flowing through it
SP10i - How do you choose the best value for a fuse?
- Fuses are typically found in 3A, 5A, and 13A.
- You want to pick one that has a current higher than what the current of the appliance is but not to high.
- This way it will stop a fualty appliance but not a properly functioning one.
- If an appliance has a current of 3A, you would pick a 5A fuse. 3A would be too low and 13A would be too high
SP10i - What are circuit breakers and how do they work?
- Circuit breakers are automatic swtiches that detect a rise in current and automatically switch off the supply safely.
- They are an alternate to fuses.
SP10i - Why are circuit breakers more advantageous than fuses?
- They can just be turned back on rather than having to buy a new fuse
- They work quicker.
- You elliminate the risk of an accident occuring while the fuse is melting
SP10i - What are the colours of the earth, neutral and live wires?
- Earth wire: Green and yellow
- Neutral wire: Blue
- Live wire: Brown
SP10i - Why may fuses be more advantageous than circuit breakers?
- Fuses are cheaper
- More practical for small scale uses (e.g. small appliances)
SP11a - Describe the movement of electrons and the charges involved when you rub an acetate rod with a cloth.
- Both objects start off as neutral.
- Electrons move from the acetate rod to the cloth so the acetate rod ends up positive and the cloth ends up negative.
SP11a - Describe the movement of electrons and the charges involved when you rub an polythene rod with a cloth.
- Both objects start off as neutral.
- Electrons move to the polythene rod from the cloth so the polythene rod ends up negative and the cloth ends up positive.
SP11a - Describe what will happen when you hang two rods next to each other with:
- Positive and positive charges
- Positive and negative charges
- Negative and negative charges
- Repel
- Attract
- Repel
SP11a - Explain how charging with induction works. (Use a balloon a jumper and a wall as an example)
- If you rub a balloon against a jumper, the friction causes electrons to transfer from the jumper to the balloon.
- The balloon now has a negative charge
- When brought close to a wall, the negative charge of the balloon repels the electrons in the wall
- The protons are brought closer to the surface of the wall as they are attracted to the balloons negative charge
- The balloon is attracted to the positive charge on the surface of the wall causing it to stick
- The wall has an induced charge
SP11b - How might you become charged while walking along a carpet?
Friction between your feet and the floor and slight friction between you and the air builds up charges.
SP11b - After gathering charge, how may you become discharged?
- By touching something made of conducting material, the electrons will jump to the object and head to the ground.
- You may experience a small electric shock
SP11b - Explain how lightning occurs.
- Static electricity builds up in clouds due to friction between ice and water particles in air currents.
- The negatively charged particle move towards the bottom of the cloud.
- As the ground is neutral, it is relatively positive to the cloud and so when the charge in the clouds is too great, they jump to the ground to discharge.
- This produces a spark which is lightning.
SP11b - How may a tall building protects an area from lightning.
- A tall building may install a lightning conductor.
- This would be a metal structure that would be the tallest structure in an area that runs through the centre of the building to the ground.
- This means that a cloud will discharge through this which wont affect the surrounding areas.
SP11b - Explain the safety feature that protects airline tankers and aircrafts.
- As high amounts of fuel pass through the nozzle at a fast rate, this build up friction which charges the fuel droplets.
- Once they have built up a great charge they want to discharge.
- This would create a spark which would light the fuel causing an explosion.
- The bonding line is attached which earths the aircraft so that the charge flows through easily to the ground without any spark.
SP11b - Why don’t cars need a bonding line at petrol stations.
The pipes and the car’s tyres earth the car already.
SP11b - Name some uses of static electricity.
- Electrostatic sprays:
- Spray paint
- Pesticide
- Printers
- Electrostatic precipitators
SP11b - How do electrostatic sprays work?
The nozzle contains electrodes which negatively charge the spray droplets. This leads to two things:
- The like charge between all droplets spread them out
- The negative charge attracts to the relatively positive object/crop and then charges it by induction to stick
SP11b - Name some advantages of electrostatic sprays
- Since they spread out there is wide coverage
- Since they attach through static induction there is even coverage
- Since all the droplets attach, less spray is wasted
SP11c - What is a force field, and what is an electrostatic field?
- A force field is the area around an object in which an object will experience a force and so…
- An electrostatic field is the area around an object where a charged object will experience a force
SP11c - What does a negative and a positive point charge diagram look like
- Both are a dot with equally spaced lines originating form the centre.
- In a positive one there are arrows away and in a negative one they are towards
SP11c - What will be the difference between two field diagrams if one has a stronger charge
There will be more lines as they will be closer together
SP11c - How do you know where the field is strongest?
Where the lines are closest together
SP11c - What are the four rules about field lines?
- Lines never cross
- The closer the lines are is where the field is strongest
- Start on the positive charge and end on the negative charge
- Shows the direction of force on an object
SP11c - What do two oppositely charged parallel plates form?
A uniform parallel electrostatic field
SP11c - If an alpha particle is placed into a uniform parallel field where will it move?
Towards the negatively charged plate.
SP13a - Explain how a loop of wire can gain an induced current using a magnet.
- A magnet has a magnetic field around it.
- Once it moves throughout the wire, the field induces a P.d. in the wire which creates a magnetic field opposite to original change.
SP13a - How does an alternator work?
- A coil of wire wrapped around an iron core is rotated inside a magnetic field
- Wires from the coil are connected to slip rings on the axle of the coil
- The slip rings make electrical contact through carbon brushes
- This produces an alternating current
SP13a - How does a dynamo work?
Same concept as an alternator except:
- The wires are connected to a split ring commutator
- The commutator is connected to the carbon brushes
- Every half-turn the connections are swapped
- Thus, this produces a direct current
SP13a - How do microphones work?
- (The opposite to loudspeakers)
- Sound waves cause vibrations in air pressure
- The pressure causes a diaphragm to move back and forth
- The diaphragm moves a coil of wire back and forth
- This causes the coil which is wrapped around a permanent magnet to gain an induced voltage and current
- The amplitude of the wave affects the volume
- The frequency affects the pitch
- Converting sound energy into electrical energy
SP13a - How do loudspeakers work?
- (The opposite to microphones)
- An a.c. voltage passes througha coil
- This moves the coil along a permanent magnet
- The coil hits the diaphram causing it to vibrate
- This creates soundwaves
- The higher the current, the larger the frequency and amplitude
- And so the volume and pitch is higher
- Converting electrical energy into sound energy
SP13b - What is the national grid?
The system that connects power stations to homes to provide electricity nationally
SP13b - What are transformers, both step-up and step-down?
Transformers are (not robots in disguise) devices that alter the voltage and current of electricity.
- SU increase voltage; decrease current
- SD decrease voltage; increase current
SP13b - Describe the process of transferring energy from power stations to houses and factories.
- Electricity is generated at the power station (11kV)
- Stepped up (400kV) for transmission lines
- Stepped down (33kV) Where some is used in large factories
- Some is stepped down further (11kV) for small factories
- Rest is stepped down instead (230V) to be used in houses shops etc.
SP13b - Why is electricity stepped up before transmission?
- A higher voltage means a lower current.
- A higher current would mean a higher power loss (P = I²xR).
- So the lowest possible current is attained so that the least amount of energy is lost by heating.
- Low resistance wires are also used (thicker).
SP13b - What is the structure of a transformer?
A primary coil (connected to an a.c supply) and a secondary coil with differing amounts of turns, wrapped around an iron core.
SP13b - How do transformers work?
- Changing a.c current supplied
- This produces a changing magnetic field in primary coil
- The iron core is induced and carries this changing magnetic field
- This creates a changing magnetic field in the secondary coil
- This induces a changing a.c voltage in the wires connected to the secondary coil.
SP13c - What is the voltage current transformer equation and what does it assume?
V(p) x I(p) = V(s) x I(s)
[assuming that the transformer is 100% efficient]
SP13b - Which equation links voltage and turns across coils?
V(p)/V(s) = T(p)/T(s)
V = Voltage across coil
T = Turns in coil
SP13c - What are the equations for power and energy?
- P = I x V
- E = P x t , so
- E = I x t x V
SP14a - What does kinetic theory state?
Everything is made of tiny particles
SP14a - Describe the properties of a solid
- Rigid
- Fixed shape
- Fixed volume
- Cannot be compressed
SP14a - Describe the properties of a liquid
- Not Rigid
- No fixed shape
- Fixed volume
- Cannot be compressed(ish)
SP14a - Describe the properties of a gas
- Not Rigid
- No fixed shape
- No fixed volume
- Can be compressed
SP14a - What happens when a substance changes state? (In terms of particles)
- The particles change their arrangement
- This leads to a change in density
- The mass is conserved as the amount of particles remains
- This is a physical change as it can be reversed and no new substances are formed
SP14a - How does the density of a substance change between states and what is the exception?
- Generally, as substances go from solid → liquid → gas, they become less dense
- This is because the particles become more spread out meaning there are less in a certain volume
- Water is the exception to this as ice is less dense than liquid water
SP14a - What is density inc. formula?
Density is a measure of how many particles are packed in a space
Density(g/cm³) = mass(g) ÷ volume(cm³)
(ρ = m x V)
SP14a CP - How do you find the density of an irregularly shaped object?
- Set an electronic balance to 0 then place the object on it and record the mass
- Set up a displacement can leading into an empty measuring cylinder and fill the can with water
- Place the object in the can. If it floats, then push it down till it is just under the surface of the water
- Read the value for the volume of water in the measuring cylinder (from the bottom of the meniscus)
- This is the volume of the object. Do mass/volume to find the density
SP14b - What is thermal energy?
The energy stored in the movement of particles that has been transferred to the system by heating
SP14b - What is temperature?
A measure of the average speed/movement of the particles in a substance
SP14b - What is specific heat capacity?
The amount of energy required to increase the temperature of 1 kg of a substance by 1°C (The diagonal lines of a heating curve)
SP14c - What is the formula for specific heat capacity?
ΔQ = m x c x Δø
Change in energy(J) =
mass(kg) x specific heat capacity(J/kg°C) x change in temperature(°C)
SP14b - What is specific latent heat?
- The amount of energy required to change the state of 1kg of a substance (The horizontal parts of a heating curve)
- This energy is given out when the doing the opposite state changes are equal to how much it takes
- (energy needed for evaporating = energy released form condensing)
SP14c - What is the formula for specific latent heat?
Q = m x L
Energy = mass x Specific latent heat
SP14b - Describe the appearance of a heating curve describing what is happening
- Time on x-axis temperature on y-axis
- There will be a diagonal line going up steadily upwards
- Eventually it will plateau and be a horizontal line for a bit
- It will then continue to rise diagonally then plateau and then rise once more
- The diagonal lines are where energy is transferred and stored as thermal energy and increasing the temperature
- During the plateaus, the energy is being used to overcome the forces that hold the molecules together resulting in changes of state
SP14d - What is the temperature of a gas and how can it increase?
- A measure of the average kinetic enegry of the particles in the gas
- By heating it up (providing thermal energy) the particles will start to move faster meaning a higher temperature
SP14d - Why does an increase in temperature lead to an increase in gass pressure (for a fixed mass of gas)?
- A higher temperatures means that the particles in the gas are moving fatser.
- This means that they will have more frequent collisions with the walls of their container.
- This means that the force exerted on the container is higher leading to a higher temperature.
SP14d - What is the unit for pressure?
pascals (Pa)
[where 1 Pa = 1 N/m²]
SP14d - What is absolute zero?
- Once the temperature of a gas has reduced to -273°C (or 0K) then the particles in the gas have a pressure of 0 meaning they aren’t moving.
- This is only theoretical as gases would normally condense to a liquid once reaching this low a temperture
SP14d - What is the kelvin scale and how do you convert between celcius to kelvin v.v?
- The kelvin scale has the same intervals as celcius but 0 K is equal to absolute zero (-273°C)
- To convert K - °C - 273 and °C - K + 273
SP14d - Describe the relationship between kelvin and the avergae kinetic energy of gas
Directly proportional
SP14e - What is gas pressure?
When gas particles hit a surface, they produce a net force acting at right angles to the surface. We detect this as gas pressure
SP14e - Why does decreasing the volume of gas (at a fixed mass and temperature) increase the pressure?
- Inside a container, the pressure acts at right angles to the walls
- If the same number of particles are in a smaller space, they will hit the walls of the container more often
- This means the force on the walls increases. We detect this as a higher pressure
SP14e - What equation links pressure and volume for a fixed mass and temperature?
- P1 x V1 = P2 x V2
- This means that an increase in pressure or volume will cause a decrease of the other by the same proportion
- They are inversely proportionate
SP14e - Why does pumping a bike tyre up increase the pressure of the pump?
- More air is forced into the typre when you pump it
- This increases the number of gas particles in a fixed volume
- As a result, there is an increase in the frequency of collisions between gas particles and the (inner) surface of the tyre
- This leads to more force exerted on and thus an increased pressure in the tyre
SP14e - Why does the temperature of a tyre increase as you pump it?
- Each time you push the pump handle, the force is transferring energy to the gas inside the pump (This is work done)
- As the piston of the bike pump moves, the speed (KE) of any particles inside the particles increases as they bounce off it
- This means that the average speed of the particles has increased and we detect this as an increase in temperature
SP15a - What are the three things a force can do to an object?
- Change shape(/size)
- Change direction
- Accelerate (Decelerate)
SP15a - What is the name for a force changing the shape of an object and what is required for it to occur?
It is called deformation and requires two forces rather than just one.
SP15a - What does it mean if an object elastically deforms?
The forces change the object’s shape but it returns back to its original shape when forces are removed. (e.g spring, diving board, and archer’s bow.)
SP15a - What does it mean if an object inelastically deforms?
The forces change the object’s shape and it doesn’t return back to its original shape when forces are removed. (e.g Clay, Blu-tac, and spoons.)
SP15a - How may some objects behave elastically and inelastically?
Some objects (like springs for example) will behave elastically. However, when the forces exceed a certain amount, they will become permanently deformed, behaving inelastically and keeping its new shape.
[Life Lesson #44: Don’t overextend yourself]
SP15a - What is the extension of a spring?
The change in length of a spring when a force is applied
New length - old length = extension
SP15a - How would you describe the relationship between force and length of a spring
- It is a linear relationship (straight line) as long as the spring behaves elastically.
- Once it is permanently deformed, the relationship is non-linear (curved).
SP15a - What is the relationship between extension and force of a spring and rubber band?
- Spring: They are directly proportional as it would be a straight line through the origin.
- Elastic band: It behaves completely inelastically with a non-linear relationship
SP15b - What is a spring constant?
The force (N) required to produce and extension of 1 metre
SP15b - What is the equation linking force and spring constant?
F = k × x
Force (N) = Spring constant (N/m) × Extension (m)
SP15b - What is the relationship between force and extension?
F ∝ x(Directly proportional)
SP15b - What does the gradient of a Force/extension graph show you?
Sign gradient is Δy÷Δx it would be force/extension which will give you the spring constant of a spring
SP15b - How may you be able to tell that a spring has a higher spring constant by holding it?
Stiffer springs have a higher spring constant (As they require more force to extend)
SP15b - How do you calculate the work done when stretching a spring?
E = 1/2 × k × x²
Energy transferred by stretching (J) = 1/2 × Spring constant × Extension²
SP15b CP - Describe how to find the spring constants of different springs.
- Set up your equipment as shown
- Measure the length of the spring without any weights at eye-level
- Add 1 newton (100g) weights one at a time, measuring the new length at eye level each time
- Take away the original length from all your values to get the extension
- Repeat a few times and take the average of your results for reliability
- Plot a graph of force/extension and calculate the gradient of the line. This will be the spring constant
- If you want to find the work done for a particular extension, square that extension, divide by 2 and then multiply by the spring constant
SP15c - What is the formula for pressure?
P = F ÷ A
Pressure (Pa) =
Force [normal to surface] (N) ÷ Area of that surface (m²)
SP15c - What are the units for pressure?
Pa - Pascals, which is equivalent to N/m²
(however the m in N/m² can be changed to any other metric length value but won’t be equal to 1 Pa)
SP15c - What are fluids?
Liquids or gases
(Because they f̶l̶o̶o̶o̶d̶ flow)
SP15c - What is atmospheric pressure?
The pressure exerted perpendicular to any surface by the air at all times. It is highest at sea level around 100,000 Pa (1 atm)
SP15c - What two things affect the pressure exerted by a fluid?
- Depth of the fluid: The more particles above you, the higher pressure you will experience as more particles can produce a higher force. This is why pressure is highest at sea level and reduces as you increase altitude
- Density of fluid: The denser the fluid you are in, the more particles there are in a fixed volume, the more particles can produce a force. This is why water pressure is higher than air pressure
SP15c - When calculating total pressure when underwater, what must you do?
Find the pressure exerted by the water and add 100,000 Pa of air pressure
SP15c - Why does a bag of crisps sealed at sea level expand when at higher altitudes?
- When sealed at sea level, the air inside the bag will around 100,000 Pa
- When taken to a higher altitude, the pressure outside the bag decreases
- As the pressure inside the bag (acting outwards) is greater than outside the bag (acting inwards), the bag expands
SP15d - What formula calculates the pressure due to a column of liquid?
P = h × ρ × g
Pressure [due to column] (Pa) =
height of column (m) × density of fluid (kg/m) × gravitational field strength (N/kg)
SP15d - What is upthrust?
The upward force exerted on the bottom of an object in a liquid.
SP15d - How do you calculate upthrust?
Difference in pressure between top and bottom of the object multiplied by the surface area of the bottom of the object
[Upthrust = Δh × ρ × g × surface area (m²)]
OR
Upthrust is the weight (in Newtons) of the liquid displaced when an object is placed in the liquid
SP15d - If an object is floating what does this mean?
The density of the object is less than the liquid it is in. The lower the density, the better it floats (more will be above the liquid surface)
SP12a - What is a permanent magnet?
A magnet that always has a magnetic field
SP12a - What is a temporary magnet?
A magnet material that only has a magnetic field when in the field of another magnet.
SP12a -When a temporary magnet enter a magnetic field and becomes magnetised, what can you say it is?
It is now an induced magnet
SP12a - What are the four magnetic materials?
- Iron
- Steel
- Nickel
- Cobalt
SP12a - What piece of equipment can be used to find the magnetic field of a bar magnet?
A plotting compass
SP12a - What do two opposite parallel magnetic plates create?
A uniform parallel magntic field
SP12a - What do the field lines aorund a bar magnet look?
- They are going form north to south, increasingly spaced out the further away from the magnet.
- They go in curves around the outside
SP12a - How do we know that the earth has a magnetic core?
- It has field lines similar to that of a bar magnet around it.
- We can see this through compasses.
- It is a core made of nickel and iron.
SP12a - What is the key thing to remember about the earth’s poles?
Its geographic north pole is its magnetic south pole and vice versa
SP12b - What does the direction of the magnetic field around a wire depend on?
The direction of the current
SP12b - What can we use to figure out the direction of the current and how can this be done?
- Curl your right hand into a fist and stick out your thumb.
- Point your thumb in the direction of the current and the direction your finger curl aorund is the direction of the magnetic field?
SP12b - When a magnetic field is shown what does a cross or a dot represent?
- Cross means that the current is haeding away from you
- Dot means the current is going towards you
SP12b - What is he shape of a magnetic field around a wire?
Circular
SP12b - When you coil a wire, what is it called?
A solenoid
SP12b - The magnetic field of a solenoid is similar to that of _______
A bar magnet
SP12b - What is the magnetic fieldat the centre of the solenoid similar to?
A uniform parallel field
SP12b - What do you call a solenoid with a current flowing thorugh it?
An electromagnet
SP12b - What are the ways you can make an electromagnet stronger?
- Adding an iron core (a temporary magnet)
- Increasing the current
SP12b - What is the strength of the magnetic field around a wire dependant on?
- The strength of the current (Stronger when higher)
- The distance from the wire (stronger when closer)
SP12c - When does the motor effect occur?
When a wire carrying a current enters a uniform parallel magnetic field
SP12c - Why does the motor effect occur and what does it produce?
The magnetic field from the wire acting against the magnetic field from the uniform parallel field produces a force that acts on the wire.
SP12c - What can be used to work out the direction of the force in the motor effect?
The left hand rule:
- Set your hand so your thumb is up and your first and second fingers are at right angles.
- Your first finger represents the direction of the field.
- Your second finger represents the direction of the current.
- Once these are lined up, the way your thumb is pointing will be direction of the force
SP12c - How do you calculate the force exerted on a wire in the motor effect.
F = B I L
Force (N) =
Magnetic field strength (T) x Current (A) x Length of wire inside the UP field (m)
SP12c - What are the two units and the alternate name for magnetic field strength?
Magnetic flux density:
- T - Telsa
- N/Am - Newton per amp metre
SP12c - How do motors spin?
- The motor effect is set up so that the wire returns back to where is started.
- This means there are two sections of the wire inside the UP field with current travelling in different directions in each.
- This means that the direction of force on one will be up and down on the other.
- The wires are centered around a pivot which allows these forces to cause a turning motion.
- This is the motor effect.
SP12c - What is a split - ring commutator used for?
- Once the side of the motor’s wire that is moving upwards has made a half turn it will be on the other side but still experiencing an upward force.
- This would mean that the motor keeps spinning back and forth around that point without ever making a full turn.
- The SR commutator means that once it has made a half turn the current will be ‘reset’ and change direction so the wire that was previously having a current going forward will now have it going back.
- So the wire experiencing an upward force will now experience a downward force and vice versa.
