paper 3 Flashcards
What is the diameter of an atom?
1 ✖️10^-10 meters
Why was it named ‘the atom’ ?
Back then was known to be the smallest thing(particle ) in nature
What was dalton’s theory?
🟣🔵🔴🟢🟣🟡🔴🟣
Atoms are tiny INDIVISIBLE particles
All matter was made from atoms
Atoms in an element are identical, different for each element
Billiard ball
What was the cathode ray experiment?
Cathode rays = metal heated up inside a magnetic field
The discovery of electrons
They came from inside the particles (not indivisible)
What was the plum pudding model
Overall a neutral atom:
Random electrons in a
cloud of positive charge- evenly spread throughout
What was the gold foil experiment?
Alpha particles were sent through gold foil
99% passed though
1% of this deflected
What is an alpha particle
2 protons
2 neutrons
What was Rutherford’s model of the atom?
The atom is mostly empty space
The majority of the mass is looted in the nucleus
The nucleus is positively charged
⚛️⚛️⚛️⚛️
What was Bohr model of the atom?
He suggested that atoms move in fixed orbit around the nucleus,
Orbits = electron shellls
What is the size of the nucleus of the atom?
1 ✖️10 **-15 meters
What is orders of magnitude ?
The size relative to the power of (x)
What is density?
A measure of how much matter is contained within a given volume
What is the density formula?
Density = mass➗volume
Kg/m 3 =kg ➗m3
Why are solids more dense than gas?
Particles spread out more and therefore have a higher volume
What is temperature?
A measure of the average kinetic energy of particles in a substance
What is kinetic energy
How fast particles are vibrating/ moving
Measured in J - joules
What are the units of temperature?
*conversion of the two
Kelvin or Celsius
273k = 1 🅾️C
What are physical changes ?
Eg : changes of state & dissolving
No new matter is produced
Particles just arranged differently
Easily reversible
What are chemical changes ?
Eg : burning & chemical reactions
New substances are produced
Difficult to reverse
How do you measure the volume of an irregular object?
Fill the eureka can to the top
Place object in
Make sure the spout is n a measuring beaker
The amount on the beaker is the volume
What is specific heat capacity?
The heat energy required to raise the temperature of 1kg of a substance by 1 kelvin.
A.K.A : how easy or difficult it is to change the temperature of a substance.
The lower SHC means less energy is required
What is the specific heat capacity equation?
E = m ✖️S.H.C✖️temperature change(ø)
J= kg ✖️J/kgk ✖️K / °c
In the S.H.C practical, how could you have it more accurate/efficient?
Put a lid on
Use an insulating container
Add conducting gel between object and container
Submerge the heater fully
What is potential energy?
The energy used to change the position of the particles (changing state - intermolecular bonds)
What is specific latent heat the measure of?
potential energy
What is specific latent heat of fusion?
The heat energy transferred when 1kg of a substance changes from solid to liquid state
(Melting/freezing)
What is the latent heat of vaporisation ?
The heat energy transferred when 1kg of a substance changes from liquid to gas state.
(Evaporating/condensing)
What is the specific latent heat equation?
Energy = mass ✖️S.LH(v/f)
J= kg ✖️j/kg
E=ML
What is the equation for pressure ?
Pressure = force ➗area
Pa = N ➗m^2
How do gases exert pressure?
The particles move in high speed , random directions.
Collision with the walls of the container exerts a force- a net force on the inside of the container (surface) determines the pressure
How does temperature affect pressure?
The more temperature, the faster the particles move, the more frequently the particles collide with the container walls, the more force is exerted resulting in more pressure.
What was Rutherford expecting in his gold foil experiment?
He expected the alpha particles to pass right through as the positive charge was assumed to be spread out
How does temperature affect gas pressure?
As temperature increases particle have more kinetic energy. The particles collide with a greater force at the wall. Leading to a higher resultant force from the wall , leading to higher pressure.
The two are directly proportional as long as volume is constant.
what is the atmospheric pressure on earth?
100 kilo pascals
100,000 pascals
what is the relationship between the pressure and volume of a gas?
pressure and volume are inversely proportional as long as temperature is held constant.
on a graph the line would have a curved L but wouldn’t tough the axis of the graph
what happens to the pressure as the volume is halved?
the particles collide twice as often (as there is twice as less space between the particle and the wall. )
Therefore the force exerted by gas particles per unit of time doubles , doubling the pressure of the gas.
What is the equation for two variables of pressure and volume?
P1✖️V1= P2✖️V2
The product of pressure and volume stays the same before and after a change
What happens when a gas is compressed ?
A force is required to move the gas particles together.
Work= force ✖️distance
Therefore work is done on a gas. The particles gain kinetic energy , move faster, raise in temperature
What happens when a gas is expanded?
The gas particles apply a force, work is done (energy is transferred), the gas particles lose kinetic energy , move slower, a decrease in temperature
What is the earth’s atmosphere and why does it have it?
A layer of gases, near earth due to it’s gravitational field
What happens to the atmospheric pressure as you go higher up and why?
It decreases , because there are fewer gas particles due to it’s weaker gravitational field
Which state of matter has more potential energy?
Gas ,because it has weak intermolecular bonds. This means that a lot of energy has been transferred to it to weaken these bonds
Why is the pressure of a bottle highest at the bottom?
It has a large weight of liquid
How does pressure in a liquid vary with depth?
The pressure in a liquid ONLY depends on the depth below the surface.
More width, more mass of water, more weight, more force
Pressure and depth are directly proportional
How does the density of a liquid affect the pressure?
The higher the density , the more mass, the more weight force, higher force = higher pressure
What is the liquid pressure equation?
Ro GH
Pressure= density ✖️depth✖️gravitational field (10N/m)
Describe up thrust
A force that occurs whenever a body is immersed within a fluid.
Because of a pressure difference between the top and bottom fluid
What is the difference between the atoms and particles?
Particles can be atoms , molecules or ions.
An atom is a single neutral particle
Why do gasses have a low density?
They occupy more volume, as there is more space between the particles, as they have more energy.Resulting in a lower density
How does the depth affect the pressure?
More depth , means more mass, which earns more density, which means more pressure
What is archimedes principle?
The upthrust experienced by a body is equal to the weight of the fluid displaced
What is the formula for upthrust?
*upthrust is the weight of liquid displaced
Force = ro g h a
Force = density ✖️gravitational field strength ✖️height✖️surface area
Upthrust = ρghA
When will a body float, sink and rise
Float:
mg= ρghA
Rise :
Mg<ρghA
Sink:
Mg> ρghA
What happens when the atmospheric pressure is greater inside a ballon that it’s surroundings?
does density of water vary with height ?
NO, trick question . The density of water is constant.
The pressure increases tho
Under what circumstances will a body float?
Under what circumstances will a body sink
In circuit A , the total resistance is less than the smallest resistor value
In circuit B , the total resistance, is an addition of the two values of resistance
where does pressure produce a force?
the net force is produced at right angles to any surface
How many seconds in a hour, how many meters in a mile
3,600s = 1h
1609m = 1 mile
How can a force change an object
It can change the shape or the motion. It can accelerate a body.
Forces are represented with Newtons(Vector’
What is newton’s third Law?
When two bodies interact they exert a force on each other , equality in size but opposite in direction
Give an example of a non contact force
Gravitation field, magnetic, electrostatic
A free body diagram shows
The result force
How do you calculate free bodies in the horizontal and vertical plane?
Pythagoras Theorem , but make sure the diagram is tip to head
To find the direction of the pythagora’s Theron :
Find the degree of the angle using trig.
The angle comes off at the new line and thE largest quantity
How would you resolve a force?
You have to find the horizontal and vertical plane of a diagonal line . You would use trigonometry using the angle and the resultant force. Then do two separate equations to find the two separate values.
Or scale diagram
What is Newton’s first law?
A body will remain at rest on continue at uniform velocity unless acted upon by a resultant force
What is inertia ?
How difficult it is to change the velocity of a body.
The greater mass, the greater interia
What is Newton’s second law?
The acceleration experienced by a body is directly proportional to the resultant force
What is the equation of newton’s 2nd Law
F= M A
N= kg m/s**2
What is magnitude?
The size of something
What is the difference between a scalar and a vector quantity ?
A vector has magnitude and direction whereas a scalar quantity only has magnitude
What is acceleration?
The rate of change of velocity.
If direction or speed changes so does acceleration
V - U
———
T
Why is a body moving in a circle at constant speed have a resultant force?
It’s changing direction and therefore velocity, constantly accelerating which means (N’s 1st law) there is a resultant force.
This resultant force is known as centripetal force
What is terminal velocity?
Constant velocity , zero resultant force
Describe a parachuter’s journey
- Weight acts down, no a lot of drag, RF increases down, acceleration, increasing velocity
- Air resistance increases to the point where RF is zero, terminal velocity - no acceleration & constant velocity
- Remains until parachute is opened, SA increases, increasing drag. RF is acting upwards, decreasing velocity
- As velocity decrease so does drag so eventually the RF becomes zero again, terminal velocity 2, contact velocity, zero acceleration
Define momentum
How difficult it is to stop a moving body. The two factors affecting this are mass and velocities.
(A vector value)
How do you calculate momentum? 🅿️
Mass * velocity = momentum
Kg * m/s = kg m/s
What is the law of conservation of momentum?
The total momentum before an event is equal to the total momentum after an event .
How do you apply the LofM when two stationary bodies push and move away from each other?
Eg (explosion)
The total momentum before and after must equal zero , as they were stationary.
To calculate a total:
. Calculate the first object using P = mv
. Then calculate the second object by knowing the fact the Momentum is negative, to equal zero, as they were going in opposite directions
How do you use the L of C when two bodies collide and move off together?
Calculate the total before , by calculating each separate component’s momentum and adding them together.
Calculate the total after but appreciate it as one value , use the momentum of previous to find out other variables
What is work?
The transfer of energy .
Whenever a force acts upon an object, work is done
What is the work equation?
Work done = force * distance
J = N *m
What happens in term of energy when work is done?
Energy is transferred from one form to another.
Eg : kinetic to gravitational potential energy,
When a body is lifted
What is power?
The rate of energy transfer
What is the power equation?
P = E/T
W= J / s
How do you calculate the gravitational force?
Gravitational force = mass * gravitational field strength
N = kg * (N/ kg)
The gravitational field strength is always 10 N/kg on earth
What is the kinetic energy formula?
Kinetic energy = 0.5 ✖️mass ✖️ (speed2)
J =. Kg* (m/s)2
E= 1/2 mc squared
What is the potential energy formula?
Potential energy = mass * height * gravitational field strength
J = kg * m * (N / kg)
U=mgh
What is an elastic body?
Objects that return to their original shape when the deforming force is removed
What is the deforming force?
Stretching , compressing or bending a body to change the shape
What is a plastic body?
Objects that do not return to their original shape when the deforming force is removed
What body is a spring?
Elastic, as they are designed to return to their original position. However if too large of a force is applied they will break.
What is Hookes Law?
The extension of a body is directly proportional to the force applied as long as the limit of proportionality is not exceeded
What is the equation for Hooke’s Law
Force exerted by spring = K✖️extension
N = (N/m) ✖️m
How do you find the extension?
New length - original length
What is the spring constant a measure of?
How stiff the material is.
The larger the konstant ,the stiffer it is
😖
What assumption is made when calculating Hooke’s Law
The limit of proportionality has not yet been reached
On a force Extension graph what is the gradient?
The spring constant
What does a diagonal line show on a Force Extension Graph?
That it obeys Hooke’s law
What does point X show on the graph?
The limit of proportionality, the point just before the line starts to curve
What is the gradient of a distance time graph ?
Speed
What does a steeping curve mean on a DT graph?
Velocity is increasing = acceleration
What does a levelling off curve mean on a DT graph?
Decreasing velocity = deceleration
How do you find the gradient of a curved line?
Create a tangent
What is the area under a V T graph ?
Displacement
What does a steeping curve mean on a VT graph?
Increasing acceleration
What is electrostatic interaction
Occurs between charged particles where they experience a force of attraction or repulsion
What is a contact force?
They are experienced in the opposite direction to contact such as friction
Where does the reaction force act
From point of contact in the opposite direction
Where does weight act?
Always vertically downwards from the centre of the object
What does it mean for a material to be brittle?
It has all linear sections, will snap instead of stretching after the elastic limit.
How do you calculate work done on a force- extension graph
The area under the line
Who would reach the floor first If two people with a different mass jump of a building at the same time?
They would both reach at the same time.
Because F=MA
A=F➗M
F= mass✖️gravitational field (10N/m)
A=(mass✖️gravitational field (10N/m))➗mass
A= gravitational field
A= 10 same for both
What is a moment?
The moment of a force is the measure of its turning effect, about a pivot.
the greater the moment , the easier it is to rotate a body
What is formula for moment’s?
M= d ✖️force
d is the perpendicular distance from the pivot to the the line of action of force (m)
How can the moment of the force be increased?
🟢Increasing the size of the force
🟢increasing the perpendicular distance from thepivot
Are moments scale or vector quantities?
✔️ vector, mention whether they are clockwise or anti-clockwise
What is the principle of moments?
The sum of the clockwise moments about any point = the sum of anti clockwise moments about any points
*nothing is turning
What is a lever?
A force multiplier
A small force on one side of the lever , leads to a large force exerted on the body on the opposite side of the pivot
F1d1=F2d2
What is mechanical advantage?
The number of times a machine multiplies the effort force
*how easier it makes it for you ( to apply less force)
Load(F1)➗effort(F2)
What is a gear?
🟢moment multipliers
🟢 force applied between the gears is the same, the radius of the cogs the moment changes
What it the mechanical advantage of gears?
Output cog radius➗input cog radius
Largest value always as the numerator
What happens to a car when travelling up hill? (Gears)
🟢you change to a lower gear
🟢the means input gear is a small gear is connected to a larger gear
🟢a input larger moment
🟢an output smaller moment
🟢causing the wheel to turn more slowly
*Large mechanical advantage
What happens when a car is travelling down hill?
🟢you change to a high gear
🟢the means input gear is a large gear is connected to a smaller gear
🟢a input smaller moment
🟢an output larger moment
🟢causing the wheel to turn more fast
*Large mechanical advantage
How is pressure exerted in a fluid?
🔴The pressure acts in all directions, and is transmitted without loss
🔴producing a force perpendicular to any surface
How do hydraulic machines work?
(Brakes)
Diagram
🔵use the pressure exerted in liquids to multiply forces and apply them at distance
Describe the structure of hydraulic machines?
🟡two pistons are connected by a pipe full of fluid (oil)
🟡the small force applied to piston 1 acts over a small area 1 creating a pressure within the fluid
🟡 the same pressure acts at piston 2 over area 2
If area 2>area 1 means output force is increased
Which distance would be applicable ?
How are forces transmitted in a liquid ?
In all directions ,
Without any loss
what is the difference between the limit of proptionality and the elastic limit?
the limit of proportionality is the last instance where the force applied and spring constant are directly proportional (Hookes’s law) .
The elastic limit of a material is the furthest point it can be stretched or deformed while being able to return to its previous shape
What is the velocity time graph for a bouncing ball?
What is the velocity time graph for a bouncing ball?
What does it mean for an object to be levitating?
The resultant force must be zero and so the upwards force/ drags must be equal to the weight force (mg).
What does it mean to be directly proportional?
A straight line passing through the origin
What is a ‘zero error’.
When a reading is displayed of an instrument, when the true reading is zero
Part a
Part b
Part c
how many forces must be applied to stretch, bend or compress an object?
moe than one force, becuase otherwise the object would start moving and wouldn’t hold still
what is the accelertation in free fall
a = 10 m/s2
in the absence of air resistance
How do object become charged?
Transferring electrons, with the force of friction
What are fields?
A region within which object experience a force
What is essential for the three fields?
Gravitational = needs mass
Magnetic = needs anything with magnetic properties
Electric = needs a charged object
What way do electric field lines go?
(electrostatic)
Leave positive and enter negative
Positive is the long wire, negative is the short
What do charge objects experience in an electric field?
Repulsion or attraction
What is current?
The rate of flow of charge, how many electrons pass a point in a second
What is the formula for current?
I = Q➗ T
I= amps
Q= coulombs
T= seconds
What is the symbol for a diode?
A circle with a triangle , line at the end pointing in the direction of current
What is the symbol for an LEd
The symbol of a diode with two arrows coming out of the circle
What is the symbol for a fixed resistor?
A solid rectangle
What is the symbol for a variable resistor, what does it do?
A solid rectangle with an arrow going diagonally though
Vary the resistance, and the current and p.d
What is the symbol of a fuse?
A rectangle with a line going through
What is the symbol for a heater?
A solid rectangle cut into boxes
How much charge does an electron carry?
1.6 ✖️10^-19 coulombs
What is voltage?
The measure of energy per charge
V= E/ Q
What is potential difference?
Difference in voltage between two points
What is the equation for potential difference? (Energy)
V = W➗Q
V= potential difference ,v
W= work done, J
Q= charge , C
What is resistance?
The opposition to the passage of charge (current)
How does temperature affect resistance?
The more kinetic energy the positive ions have the more they vibrate up and down. Stopping them flow, reducing current.
The greater the temperature, the greater resistance
Why does current transfer energy in a circuit?
Resistance, the higher the resistance, the more energy is transferred by the current
What is the main equation for potential difference?
V=I ✖️R
V= pd, volts
I= current , amps
R= resistance, ohms
What is charge?
A property of matter ,
Electrons carry charge
What is a series circuit?
The electrons must travel through every component,
Just one loop, no branches
How does the current differ in a series circuit?
It stays the same throughout
It=I1=I2
How does the voltage differ in a series circuit?
The total voltage is shared throughout the circuit
Vt=V1+V2
How does resistance differ in a series circuit?
It’s shared out throughout the circuit
Rt=R1+R2
What is a parallel circuit ?
The electrons do not travel through the same components.
The circuit has branches
How does current differ in a parallel circuit?
It distributed between each branch
It= I1+I2
How does potential difference differ in a parallel circuit?
It is the same across each branch
Vt = V1 =V2
How does resistance differ in a parallel circuit?
1/Rt= 1/R1 + 1/R2
What p.d is required to create 1A?
100 kw
Therefore it is very unlikely that you’d be injured by an electrical currents
What is the gradient of an I-V graph ?
1/R
Opposite of resistance
What is ohms law?
The current through a component is directly proportional to the potential difference, as along as the temperature is kept constant
What does a diagonal straight line show on an IV graph?
Constant resistance
What does a steep gradient show on an IV graph?
low
resistance
What does a shallow gradient show on an IV graph?
high resistance
Explain why as the p.d increases , the component gets hotter?
Some of energy transferred as the electrons pass through the component (voltage).
more energy transferred per coulomb of charge
Some of this energy is transferred to heat
What pattern do fixed resistors follow on an IV graph
🔺Diagonal straight line (linear circuit element) - resistance is constantly
🔺Ohmic conductors (follows Ohm’s law)
How can you note temperature in an IV graph
As the p.d is increasing, so is the temperature
Describe the IV graph for a filament light bulb
🔺The resistance increases with p.d
🔺As the resistance increases as it is getting hotter
🔺Non - linear circuit element
Describe the IV graph for a diode
Forwards resistance is low
Reverse resistance is high
How does the net resistance change when you add more resistors in a series circuit?
The net resistance increases as the total current decreases
How does the net resistance of a parallel circuit change when you add more resistors?
The net resistance decreases, and will always be smaller than the resistance of the smallest resistance branch
The total current increases
What is a sensor circuit?
A circuit that turns a component on or off automatically in response to external stimuli
What is a thermistor?
A type of resistor who’s resistance in reduced greatly by heating
Inverse temp and resistance
Describe how a thermistor works
🔘in series with a fixed resistor and in parallel with a component
🔘as temperature decreases, resistance increases (more than the fixed resistor)
🔘as ratio of shared resistance increases so does the shared p.d
🔘as in parallel with the component the p.d also increases at it is the same
🔘once voltage is high enough the working potential is reached and it is switched on
How would you calculate sensor circuits
Use ratios and assume the same ratio for P.d as resistance ratios
What is electrical power?
The rate of electrical energy transfer
Joules per second
What is the formula for electrical power?
P=I ✖️V
P=Watts
I= amps
V= volts
What is the equation for electrical power(2) ?
P = I^2✖️R
P= watts
I= amphs
R=ohms
What are watts a measures of?
The amount of joules transferred in a second
What is a diode?
A semi- conduct that allows current to flow easily in one direction, but restricts it in the other
What is an LDR ?
A light dependant resistor.
When the light intensity decreases, the resistance increases.
Why does moisture decrease the build up of static charge?
Moisture can conduct charge, not allowing it to build up
How does the amount of resistance wire affect the current?
The more the wire , the less the current
The less wire, the more current
How is the relationship between temperature and p.d shown on a graph?
A curving gradient of resistance as p.d increases
How is current calculated?
if given a certain amount of electrons
The number of electrons ✖️1.6*10^-19 coulombs
What happens to the electrons when the current is doubled?
The amount of electrons present doubles
What do the electrons look like in a wire with no current?
Electrons are present , but all are moving in random directions. They all chance, each other out with an overall 0 charge.
How do thermistors decrease their resistance with increased temperature?
The ions vibrating faster < temperature releasing electrons from their shells- decreasing the resistance
Why are their differences in voltage between the wires?
The cell/ battery creates chemical reactions which bunch up the electrons in places of the wire. So the electrons will travel from a high point to a low point , creating a p.d
Why do the electrons travel from high voltage to low voltage?
Everything wants to have a lower energy state in the world.
describe the relationship between current and resistance
describe the relationship between temperature and resistance
Mention how it impacts current
what are the conditions needs for charge to flow?
- a source of potential difference
- a closed circuit
What is a force?
A push/pull
How does the distance affect force?
All three get smaller as you move further away from the mass/magnet/charge
Describe magnet
An object with a magnetic field
Exert a force on a magnetic material
How do field lines reflect the magnetic strength?
The more denser the field lines are , the stronger the magnetic field
What are permanent magnets?
Always has a magnetic field
Attract/repel other permanent magnetic and also non magnets
How do permanent magnets exert a force on non-magnet?
When brought close , non magnets have magnetism induced in them.
What direction do magnetic field lines go in?
From North Pole to South Pole
Describe the 🌎’s magnetic field
The geographic North Pole is the magnetic South Pole.
Because the magnetic north Pole points to the geographic south Pole
What happens when two magnetic fields interact?
The lines will best around
Creating a high density of field lines between the two magnets, however weak in other places (weak attraction)
What happens when current flows in a wire?
A magnetic field is generated around it
What is a magnetic field?
A region of space within which a magnet experiences a magnetic force of attraction or repulsion.
Describe the look of magnetic fields exist around wires?
Concentric rings
The space between the lines increases with increasing distance
How does a stronger current affect the magnetic field?
Stronger magnetic field
the space between the lines are smaller
What is the corkscrew rule?
RIGHT HAND
Thumb = direction of current
Fingers= direction of magnetic field
What is a solenoid?
A device that increases the strength of the magnetic field around a current carrying wire
How do you make a solenoid?
A wire wrapped many times around a metal that can be magnetised
*not permanent magnets
What is an electromagnet?
A magnet which runs on electricity, the field can be switched on and off
What effects the strength of a solenoid?
🧲coils in the wire
🧲size of current
🧲material of the core inside the wire
How would you show there is a field around a solenoid?
Use iron fillings
What is the relationship between the distance and the strength of a wire?
inversely proportional
The strength is the square of the distance
Eg: double distance , strength decreases by a factor of 4
What is magnetic flux density?
The number of lines of force passing though a unit of area of material
Measured in Tesla’s
Newton per amp meter
What does a circle with an x mean ?
The arrow is going into the page
What does a circle with a point mean?
The arrow is coming towards me
How do you calculate the force on the conductor?
F = BIL
F= force (N)
B= magnetic flux density (T)
I= current (A)
L= length of conductor (m)
What does Flemings left hand rule state ?
The direction of force exerted is always perpendicular to both the direction of the magnetic field and the direction of the current in the wire.
How do you use Fleming’s left hand rule?
Thumb =force
First finger= field
Second finger =current
FFC
What does an electric motor do?
Uses the motor effect to transfer electric energy to kinetic energy
What does an electric motor consist of?
A loop of wire , with a current in a magnetic field
Why must the current be reversed every half turn?
If the current was not reversed , the direction would be (force).
Causing it to spin anti clockwise and then clockwise,
Shaking and flopping -not turning
What does a split ring commutator do?
Reverse the direction of the current every half turn.
Allowing the coil to rotate in the same direction
Why does increasing the current increase the force ?
( motor effect )
1.Magnetic field lines exist around a wire with a current
2. The larger the current the greater magnetic fie,s strength in the interaction between the wire and permanent magnet
Why would some motors use electromagnets rather than permanent?
Electromagnets produce stronger fields
Describe the motor effect :
🔘a looped wire carrying current is placed within a magnetic field
🔘therefore the wire experiences a force, causing it to turn
🔘to make it spin the same direction a split ring commutator is required to reverse the current every half turn
🔘this allows the loop to spin in one direction
🔘as it spins electrical energy is transferred to kinetic energy
What is an electrostatic field in motion?
A magnetic field
How do you draw a magnetic field around current carying wires?
Use the right hand corkscrew rule.
The direction the thumb points in is the North Pole
How do you draw a magnetic field around a solenoid?
Use the right hand corkscrew rule, but align your fingers with the coils (thumb points to the North Pole).
Draw as a bar magnet
*but the strength of the field lines is now greatest in between the coils
Why does a current carrying wire have a magnetic field?
The electrons within the wire have an electrostatic field, as they move the electro static field is in motion creating a magnetic field
What is a magnetic field?
An electrostatic field in motion
What is the generator effect (electromagnetic induction)?
When a conductor cuts the magnetic field lines of a magnet, a potential difference is induced across the ends of the conductor
Describe the generator effect:
🟣wire with no current , within a magnetic field is experiencing a force
🟣this force is perpendicular to the direction of magnetic field
🟣as the wire cuts field lines, electrons are accelerated inducing a p.d
🟣this creates a current
What happens when the motor and generator effect take place together?
The force and current produced by the motor effect counteracts the generator effect.(law of conservation of energy)
How do you increase the size of the generated p.d?
F= increase the velocity/accelerate the wire
B= increase the magnetic field strength (bring closer/new magnets
L= increase the coils on the wire
What happens when you reverse the direction of the wire in the generator effect?
The direction of p.d is reversed
(Negative p.d)
How does a stronger magnetic field produce a larger current in the generator effect?
The stronger the magnetic field, the more dense the field lines are , the rate at which magnetic field lines are cut is faster, larger current
State Lenz’s Law
The direction of the induced p.d is such that it opposes the change producing it
How can you use the generator effect to slow down a falling lift (no cable) ?
🔴a lift with permanent magnets, inside a metal tunnel
🔴as the loft falls , magnets move past the metal surfaces of the tunnel
🔴the lifts (metal surfaces), will cut the magnetic field lines , inducing a p.d and current within
🔴the current carrying surface will interact with the magnetic field of the tunnel giving rise to a force in the opposing direction (motor effect)
🔴this force will counteract the weight force of the falling lift , causing it to fall slower🔴
What does a voltage time graph look like for a generator?
A sin graph.
*the highest peaks are for when the field lines were cut and the closest angle (90°)
Describe the alternator
*generator affect
Produced a.c (magnetic field lines as cut from above and below
Uses a slip ring(doesn’t change direction of the current)
Describe a dynamo
*generator effect
Produces d.c
Split ring (reverses the current every half turn)
How do you increase the induced p.d of an alternator?
🟣rotate coil faster (more field lines cut per second)
🟣stronger magnetic field (field lines closer together, so more cut)
🟣more coils
* doubling frequency
Compare dynamos and alternators
What are transformers?
Devices that use a.c in the primary circuit to induce an a.c in the secondary current
How do transformers work?
How do transformers work?
Describe the difference between step up and step down transformers
What is the transformer equation?
How do microphones work?
🟢generator effect
🟢sound waves hit diaphragm, causing it to move forwards and backwards
🟢so the coil attached also moves backwards and forwards
🟢the coil moves inside a magnetic field , so cuts field lines perpendicularly
🟢a p.d is now induced within coil, producing an electrical signal fed to a speaker
How do loudspeakers work?
🟢a current carrying wire, enters a magnetic field . MOTOR EFFECT. This causes the wire to experience a force
🟢as the coil moves forwards and backwards, the diaphragm moves forwards and backwards
🟢therefore creating sound waves , at the same frequency diaphragm vibrates
Describe the circular magnet
In loudspeakers,
The charge
Draw the magnetic field around a solenoid
