FULL LAST MIN Flashcards
How can energy of a system be changed
Mechanically (forces doing work), Electrically (by moving charge doing work), by heating or by radiation
What does power mean
How much work is done per second
-It is the rate of energy transfer and is measured in Watts
How do you work out power
work done/ time taken
Whats is the effect of a gravitational field on objects
non contact force- the gravittional attraction between objects is caused by their gravitational fields interacting
What is the effect of magnetic fields on objects
and electrostatic force
interacting magnetic fields cause attraction and repulsion between magnetic objects
-electrostatic force causes attraction and repulsion between electrical charges and their electric field
What are the forces that occur when objects are in contact with each other
both objects feel an equal and opposite force called an interaction pair (3rd law)
-these pairs can be shows with vectors (arrows diagram)
Objects in equilibrium have a resultant force of…..
zero (this can be stationary or moving at constant speed)
Describe a situation where energy is transferred Mechanically (by doing work)
if a box is lifted off the floor work is done against gravity which causes energy to be transferred mechanically to objects kinetic and GPE stores
Describe a situation where energy is transferred electrially
electric ions carry charge electrically from mains power supply to thermal energy store of metal plates
What is a moment
The turning effect of a force
How do you calculate a moment
force x distance
How would someone get the maximum moment/turning effect
you could push at right angles as any other angle means smaller distance so smaller moment
What is the principle of moments for a an object in equilibrium
Sum of clockwise moments is = sum of the anticlockwise moments
What do leavers do
They make it easier to do work by transferring the turning effect by increasing the distance from the pivot where a force is applied
Explain how gears transmit rotational effects of forces
They fit together to transmit turning effects by interlocking,
a larger gear is slower but creates a large moment
a small gear is faster but has smaller moment
What is meant by potential difference
driving force which pushes the charge around
higher the PT the higher the current
What is the current
Flow of electric charge (electrons) around a circuit and it will only flow if theres a potential difference
What is resistance
anything that slows the flow down
usually increases with temperature
How do you measure charge
current x time
What is charge
current is the rate of flow of charge.
its a flow of electrons
Describe the current and potential difference in a series circuit
Current is the same everywhere
PT is shared between each component
How does the Resistance change in a series in you add a resistor
It increases
Why does resistance increase with temperature
because the electrical charge has to do work against the resistance
as the current flows through a resister it heats up because the electrons are colliding with ions in the lattice resistor
-If resistor too hot no current will flow (unless thermistor)
How could you investigate a component in series
-connect a voltmeter in parallel with the component you’re investigating and ammeter in series
-change the potential difference on power supply and take several readings from the ammeter and voltmeter
for different output voltages
-Plot I-V graph to work out resistance
(make sure circuit doesnt overheat)
What would you find if you kept the PT of a thermistor the same but gradually increased the temperature
that as the temperature increases the current through the resistor decreases and the resistance decreases
Describe a test for a LDR
Carry out in dim room
- keep PT constant but slowly adjust the light level near the LDR and measure the current through LDR
- should find as light intensity increases, current increases and resistance decreases
Describe an IV graph for a diode
current only flows through a diode in one direction
diodes have high resistance in opposite direction
(so flat line and then sudden increase)
What is a thermistor and what is it used for
hot conditions resistance drops
-used in temperature detectors eg) electric kettles
car engines
What is an LDR and name some uses
Light dependent resistors
- in bright light resistance falls so current increases
- used for automatic night light lights and burgler detectors
How does resistance change in a series and parallel when you add a resistor
Series- increases resistance- makes resistors have to share PD
Parallel - decreases total resistance as both resistors have same PD and by adding another loop for resistor you are giving the current another direction so increase in current= decrease in resistance
How can we find the energy transferred in a system with a formula?
Current x Potential Difference x time
Explain why the transfer of energy leads to heating
Because as energy is transferred some is as thermal energy to thermal stores as heating usually increases resistance. so its dissipated to surroundings
How is efficiency effected by heating
it decreases
how do fuses help protect circuits from overheating
they melt and break the circuit if it gets too high
Why can a heating effect be useful
it toaster a coil of wire has a very high resistance so gives off infrared radiation to bread and cooks it
What is power
The rate it transfers energy per second
what can happen to components in a circuit if the temperature increases too high
It can cause them to melt and stop working properly
What does a power rating show
the maximum safe power an appliance can opperate at
shows the max. energy transferred between store each second
How can you work out electrical power with Potential difference
Current x PT
How do you work out Power with Resistance
Current^2 x resistance
A mains supply has a……..current
an alternating current
A battery supply has a…….current
direct current
What is the potential diffence of UK mains power supply
230V
How can you turn A.C to D.C
using a diode
Describe the neutral wire
blue-
completes the circuit
electricity flows out of this wire
has PT of 0Volts
Describe the Live wire
brown- carries the Potential difference/voltage
alternates between high positive and negative voltage of 230V
Describe the Earth wire
Green and Yellow
it has a PT of 0volts
used for safety and protecting wires
it carries current away to earth if something goes wrong
What is a double insulated appliance
doesnt have an earth wire as its already earthed
Why does touching a live wire give you an electric shock
Your body is at 0 volts like an earth wire so if you touch a live wire a potential difference is produced across your body and a current flows through you
How could a fire start in a circuit
-any connection between a live and neutral wire is dangerous as it creates a low resistance path to earth and huge current so fire could start
What do fuses and earthing do
Prevent electrical overloads which could start a fire or melt you components or give deadly electric shocks
How does a fuse work
if a fault develops in live wire, then the current flows through the case and down the earth wire
- this surge melts the fuse when current exceeds rating and breaks circuit stopping live supply
- it isolates the whole appliance so you cant get shock
What should a fuse rating be
near as possible but just higher than the normal operating current
so in event of fault it doesnt overheat and start fire
The larger the current the ……the cable needed to carry it
thicker
What is circuit breaker
some pros and cons too
instead of a fuse a circuit breaker trips the circuit so it turns off quicker than the time a fuse would melt
+they can be reset so dont need replacing as much
- but are more expensive
What does double insulating materials mean
a plastic casing (instead of metal) has no metal parts showing so doesnt need an earth wire
how does rubbing an insulator transfer electrons and create a static charge
negatively charged electrons are scraped off one material onto another
- as its an insulator the electrons aren’t free to move
- this builds up static electricity
- the material becomes electrically charged with a positive static.
Electrically charged particles exert a ……on each other
force
how do forces of attraction change with distance
further means weaker
How can an electrically charged object attract uncharged objects (with example)
Rubbing a balloon on your head transfers electrons to the balloon leaving it negatively charged
-if you hold the balloon against a wall it will stick because the negatively charges on the wall are repelled and positive charges are attracted to negative balloon
How does attraction by induction occur
If a negatively charged object is used to charge a neutral object by induction, then the neutral object will create a positive charge.
(The charged object that is brought near will always repel like charges and attract opposite charges.)
What is earthing
sending current down to the earth
provides easy route for static charge so none builds up
How do spark occur
If a potential difference is large enough, electrons can jump a gap between charged object and earth making a spark
eg)lightning
How do electrostatic sprayers work
- spray gun is charged, so paint droplets become negatively charged
- object being painted has an opposite charge to attract the fine sprays of paint
- gives an even coat as areas with paint become negative so theres no build up
- no paint shadows
How does lighting form
raindrops and ice bump causing friction and leaves top of cloud positively charged and bottom negative which creates huge voltage and spark which jumps across gap to earth as lightning
-damage homes, start fires
How can objects be earthed to stop charge building up
by connecting charged object to the ground using conductor through earthing
- provides easy route for static charge
- no build up of static so no sparks
What do electric charges do
Create an electric field around any charged object
stronger as you get closer
What happens to a charged object is placed in an electric field? and what is it caused by?
it feels a force caused by two charged objects interacting
what happens field lines between charged objects point in opposite directions
They repel
How do you get a uniform field
between two positively charged parallel plates
How can sparking be explained with electric fields (and therefore static)
- When an object is statically charged it creates its own electric field
- interactions in this field cause sparking
What is ionisation in a electric field
Electrons in the air particles to be removed
When is air not an insulator
when its ionised enough that it becomes more conductive and sparks are made
What is a permanent magnet
produces its own magentic field
What is an induced magnet
only produces a field when in another magnetic field
putting any magnetic material into a magnetic field it becomes an induced magnet
what does magentically hard mean and give examples
lose there magnetism more slowly
permanent magnets are made from magnetically hard materials
Name some uses of magnetic fields
Doorbells- electromagnets that turn on and off rapidly to repeatedly attract and release an arm which strikes a metal bell
MRI machines- magnetic fields to creat images inside your body without having to use ionsing radiation
A moving charge creates a
magnetic field
explain the right hand rule
thumb represents current curled up fingers represent the direction of the magnetic field at right angles to the current
in order to experience full force in a motor the wire needs to be at……
90 degrees to the magnetic field
if it runs along field it wont experience any force
How can you find the size of a force
Force = magnetic flux density x current x length (of conductor)
Describe how a motor works
- forces (which act on current in magnetic field) act on two arms of a current carrying coil
- they act in opposite directions so coil rotates
- the split ring commutator swaps the contacts every half turn to keep motor rotating in same direction
how can the direction of a motor be reversed
by swapping the polarity of the D.C supply or swapping the magnetic poles over
What is a solenoid
describe the field lines:
a long coil of current carrying wire
- the field lines around each separate coil of wire line up in same direction so the field is strong and uniform
what is electromagnetic induction in terms of Potential difference
induction of potential difference in a wire which is experiencing a change in magnetic field
what two situations can you get electromagnetic induction
when electrical conductor (coil of wire) and magnetic field are relative to each other
-this can be done by rotating/ moving/ changing polarity of magnet
when magnetic field through conductor changes (like in a transformer)
-this can be done by increasing STRENGTH of magnetic field, increasing SPEED, increasing TURNS ON COIL
How does a transformer work
-use electromagnetic induction to change size of Potential difference of an alternating current by: increasing number of coils on secondary coil than primary coil in step down
How do dynamos work
- generate a direct current by applying a force to rotate coil in magentic field (like in a motor)
- current is induced in coil which changes direction every half turn due to split ring communicator to keep current flowing in same direction
How do Alternators work
- similar way to dynamos, force applied to rotate coil in magnetic field with an induced current in coil
- but instead of split ring has slip rings and brushes so the contacts dont swap every half turn which produces and alternating current
How do microphones work
- using electromagnetic induction
- sound waves hit diaphragm which is attached to coil of wire which makes both move creating a current in the coil
How do loudspeaker work
-coil wrapped around pole of permanent magnet
so a.c signal causes a force on the coil
-when current reversed the force acts i different direction
-this moves the paper cone as it vibrates it as pressure causes sound waves
Describe how a power station generates electricity for the national grid
- burning fuel heats water which creates steam
- steam powers turbine
- turbine connected to powerful magnet inside generator
- the magnet spins, inducing a large voltage and a.c current and single output generated
- generator joined to national grid
How are transformers used
The high current heats up wires so energy can be wasted so to reduce this transformers are used and high voltage cables.
- Step up make Voltage really high at 400,000 V and keep current low (usually in less comercial areas like across country
- step down decrease voltage to safe usable levels for consumers like in towns and homes
What are the arrangements of particles in solids liquids and gases
- Particles in a: gas are well separated with no regular arrangement.
- liquid are close together with no regular arrangement. weaker forces of attraction compared to solids
- solid are tightly packed, usually in a regular pattern. strong forces of attraction little kinetic energy so vibrate in their fixed positions
Density does vary with …. or……
size or shape
How can you find the density of an irregular solid
measure mass on balance
using a displacement can measure volume of water displaced
Why do solids liquids and gases have different densities
- when a substance changes state although its mass doesnt change, its volume does, so since the volume changes the value for density changes too
- Solids are more dense
What does heating a substance do to energy stores
increases energy in thermal energy store
What is specific heat capacity
and equation
The amount of energy needed to change 1 kg of a substance to warm up by 1 degrees.
Change in thermal energy=mass x SHC x temp change
Describe an experiment to measure SHC of water
- measure mass of insulating container
- fill with water and measure mass again, the difference in mass is mass of water in container
- add joulemeter to electric immersion heater
- measure the initial temp then turn on power
- when temp increased by 10 degrees, record the energy on joule meter and increase in temp
- rearrange equation and repeat 3 times to find average
What is Specific latent heat
amount of energy needed to break bonds and change 1kg of a substances state
Why does temperature not change during a state change
because bonds breaking/forming so energy is used to use of release energy rather than increase the temperature
describe an experiment used to measure SPL
- fill beaker with crushes ice (can insulate with lid)
- place thermometer and record temp of ice
- gradually heat with bunsen
- every 20 seconds record temperature
- continue until boiling
- plot graph of temp against time
Whats the equation for SPL
Thermal energy = mass x SLH
how is pressure created
by colliding gas particles exerting a force
eg)in an enclosed system gas particles colliding with walls
Name Two factors which effect gas pressure
increasing temperature increases pressure as particles have more energy in their kinetic stores so collide more
-increasing volume decreases pressure as particles get more spread and our less likely to collide
Explain changing the pressure inside a container by heating or cooling
With balloon
If balloon is heated- particles gain energy and move quicker so more pressure inside balloon.
since the outward pressure of balloon is greater than inward, the balloon expands until balanced out
Why does does work on a gas increase its temperature
Because it increases its internal energy, which increases its pressure
eg) can be done mechanically with bike pump
transferring energy to kinetic store which inc. inetrnal energy and heats
what does it mean if an object has been elastically distorted?
It means it cant return to its original shape and length after the force has been removed
what is an elastic limit
point where object stops distorting elastically and begins to distort inelastically
if work is done on a spring where is energy transferred
elastic potential energy store
what its Hookes law
force = spring constant x extension
What is it called when an object stretches more for each unit of force
limit of proportionality
when graph becomes non-linear
how do you calculate work done by a spring
energy transferred in stretching =
1/2 x spring constant x extension
what does fluid pressure depend on
depth and density
as depth increases so does pressure as number of particles above that point increases
how does pressure and density vary in water
pressure increases with depth
density is the same everywhere
Equation for pressure in column of liquid=
height x density x GFS
what is the resultant force called when when force exerted on bottom of object is greater than force on top
upthrust
what is upthrust equal to in fluids
the weight of fluid displaced by object
what makes an object float
if the volume of water displaced is equal to or more than its weight
usually if an object is less dense than the fluid its in then it floats
how do submarines make use of upthrust
to sink they have large tanks filled with water to increases weight so its more than the upthrust
to rise the tanks are compresses with air to reduce weight so its less than upthrust
what does atmospheric pressure decrease with
height / altitude
as altitude increases fewer air molecules are able to collide with surface as the atmosphere gets less dense
and weight above air decreases too
How is atmospheric pressure created
by air molecules colliding with surface
