Physics Electricity Topic 2 Flashcards
Only ———- can be transferred to and from an atom. A charged atom is called an —–
electrons
ion
Two static electricity rules please state them :
build up static is caused by ——–
when certain ———- materials are rubbed together ——— charged electrons will be scraped off one and dumped on the other.
This will leave the materials ——– charged with a ———- static charge on one and an equal ———- static charge on the other.f
Opposite charges attract.
Like charges repel.
friction
insulating
negatively
electrically
positive
negative
A van de Graaff generator is like
because it
it was orginally used
it uses ?
an industrial version of rubbing a balloon on a jumper, transferring electrons from one place to another. It was originally used to accelerate electrons to very high speed.
it uses to insulators and rubs them together to create a static charge
A force field is caused by ————- these forces do not need to be …
non-contact forces
do not need to be in physical contact (touching) for an interaction of forces to take place. Attraction/repulsion of static charges is an example of a non-contact forces.
Electric field lines flow away
from positive charges and towards negative charges.
The closer together the field lines are, the
they’re always at —— angles to the surface
how can sparking be explained via electrical fields
the stronger the field.
right
sparks are caused when there is a high enough pd between charged object and the earth
a high pd causes a strong electric field between the charged object and the earthed object
the string electric field causes electrons in the air particles to be removed known as ionisation
air is normally an insulator but when it is ionised it is much more conductive so a current can flow through it this is the spark
The strength of the field depends on two things:
The size of the charge.
The distance away from the charge
the bigger the charge the bigger ———–
too much static causes ——–
as the —— charge builds on an object the potential difference between the object and the earth ——-
If the potential difference gets —— enough than ——— can jump across the gap between the charged object and the ——- this is the ——-
They can also jumped onto any earthed ———-
jump it can make
sparks
electrical
increases
large
electrons
earth
spark
object
charge (c)=
the size of current is the rate of flow of —–
current (A) * time (s)
charge
what is electrical current ?
Current will only flow around a circuit if there is a ——————
unit of current: ampere, A
electrical current is the flow of electric charge round the circuit.
potential difference
In a single, closed loop the current has the same ————
everywhere in the circuit -
value
multiple cells=
battery
what 2 things are needed for current to flow?
something to make electricity flow - a cell battery or power pack
a complete path for the current to flow
equation for charge
Q=I*T
charge measured in coulombs
=current measured in Amps * time the flow of electrons measured in seconds
electric charge
what is it measure in?
what is it carried by?
measured in coulombs is carried by electrons and gives rise to electric current when allowed to move around a circuit
Electric current
what is it measured ?
How is it measured?
measured in Amps is the rate of flow of a charge in a circuit . The size of an electric current is the amount of electric charge passing any point in a circuit per second
electrons transfer energy to components around
a circuit . For example electrons can transfer energy from a cell to a bulb
Ammeters measure ——— and are connected in ——-
current
series
Voltmeters measure —————— and are connected in ————
potential difference
parallel
The potential difference (voltage) between two points in a circuit is include units of measurement
the work done or energy transferred J per Coulomb of charge that passes between points
potential difference equation(involvingcurrent)
:
potential difference (v)= current (A) * resistance (omega symbol) (ohms)
the greater the resistance across a component
the smaller the current that flows through it
The resistance of ohmic conductors does not ——- with the current at a constant —— the current flowing through an ohmic conductor is ———- proportional to the potential difference across it
The resistance of some resistors and components does change e.g——————–
When an electrical charge flows through a filament lamp it transfers some energy to its ———– energy store which is designed to ———— resistance increases with ——— so as the current increases the filament lamp heats up more and the ———- increases.
For diodes resistance depends on ——— they will happily let current flow in one ———but will have a very high ———– if reversed.
change
temp
inversely
filament lamp or diode
thermal energy store
heat up
temp
resistance
direction
direction
resistance
Potential difference equation with work and charge
v=w/q
potential difference (V)=
work j/charge (C)
electrical resistance is
the opposition to the flow of charge
resistance is measured in
what is the symbol
a unit called OHMS
omega Ω is the symbol for OHMS
what in a circuit causes resistance?
the electrons flowing through a circuit have to push through lots of vibrating ions which resist the passage of electron flow
what elementsin a circuit decreases/increases resistance?
length of wire
heat
type of material
diameter or cross section of wire
a resistor is a device
a resistor is anything that ——-
A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit
slows down the flow
If you have two resistors in parallel their total resistance is equalt ot half the resistance of onr of the two resistors why is this:
How does this affect the whole circuit?In parallel both have same pd across them as the source
this means the ‘pushing force’ making the current flow is the same as the source pd for every resistor that you add
But by adding another loop the current has more than one direction to go in
this increases the total current that can flow around the circuit using V=IR an increase in current means a decrease in the total resistance of the circuit .
potential difference current and resistance equation what is this equation called
V=I*R
potential difference in volts =
current in amps * resistance in OHMS
OHMS LAW
what is OHMS law ?
the current through a conductor ( at constant temperature ) is directly proportional to the voltage across two points
therefore by OHMS law if the current doubles then so will voltage
as the ammeters changes position in the circuit the current ———
stays the same
as the number of bulbs increases, the resistance ——— this causes current to ——–
increases
decrease
As the potential difference increases, the current —— this makes the bulbs ——-
increases
brighter
the potential difference at the power source is split across each of the components in a series circuit. Another way of saying this is that :
the p.d across each component added together make the p.d of the power supply
what happens to the current in a parallel circuit?
the current is split between each ‘loop’ of the parallel circuit, such that theoretical current from the power. Supply is equal to the sum of the currents in each loop. In fact the current is split in each loop in ‘inverse proportion’ to the resistances of components in the loop (ie. if loop 1 had a higher resistance than loop 2) it has lower current and vice versa)
multiple resistors in a series cause the ————————– to increase
overall resistance
(think of the properties of the wire)
resistance in a wire increases as it gets
longer or thinner
adding more batteries increases the ———- and the bulbs become ———
current
brighter
adding more bulbs decreases the ———– and the bulbs become ————
current
dimmer
the resistance of components such as thermistors and LDR’s is
not constant it changes with the current through the component
the resistance of some types of a thermistor —————— as temp increases
they make useful
decreases
temp detectors e.g. car engine temp sensors and electronic thermostats
the resistance of an LDR —————— light intensity increases
They uses are
decreases as
automatic night lights, outdoor lighting and burglar detectors
how would the resistance of a wire change depending on temp
as the wire heats up , just like all other particles of matter - they gain kinetic energy and begin to vibrate
this vibration increases the resistance to the flow of current . therefore the current should go down
conductors
allow electrons to flow : there are plenty of free electrons allowing a material to do this
insulators
electrons?
prevent the flow of electrons there is an absence of free electrons and so there struggles to be a current
semi-conductors
have electrons but in order for them to become ‘free’ energy needs to be supplied to them. this can be in the form of heat or light
thermistor
what is it made of how does this affect it?
a device for which resistance will vary depending on temperature
a thermistor is made of a semi-conducting material and as such , as it becomes hotter , electrons can become free
electrons flow out of the negative terminal and towards the ————— terminal
positive
DC is definition and examples
direct current the current flows in one direction only
examples: cells and batteries
ac definition and examples and what is frequency
alternating current
alternating pd in which the positive and negative ends keep alternatinghe current constantly changes direction, how often it does is called ‘frequency’
examples mains supply from a pocket socket
amplitude is the
height of the wave
wavelength
length between two troughs
mains electricity volts and frequency
230 volts and 50 hertz frequency
what does it mean if a supply is 30 hertz
this means that the current flow changes direction and back again , 30 times per second
frequency equation =
1/time period (s)
why does touching the live wire give u an electric shock:
your body just like earth is at – V
This means that if you touch the live wire a large potential difference is produced across your body and a ———- ——- through u
this causes a large electric shock that could:
even if a plug socket or live wire is turned off (e.g the switch is —-)
there is still a danger of an —————– a current isnt flowing but there is still —— in the live wire.
0 current flows
injure , kill
open
shock
pd
electrical apliances are designed to transfer energy to components in a ——- when a ———– ——-
a good example is the kettle it…
of course no appliance transfers all energy completely usefully the higher the —— the more energy is transferred to the energy stores of components
circuit
current flows
transfers energy electrically from the mains ac supply to the thermal energy store of the kettlr of the heating element inside kettle
current
In a parallell circuit each component is ——-connected to the +ve and -ve supply (except ammeters which are always connected in ——).
If you remove or disconnect one of them it will ——– effect the others at —–
This is obviously how most things must be connected, for example in cars and in household electronics. You have to be able to switch everything on and off ——–
seperately
series
hardly
all
separetely
mixture
In parallel circuits all components get the full source —– so the voltage is the —– across all components
In parallel circuits the total ——- flowing around the circuit is equal to the total of all the currents through the seperate ——–
In a parallel circuit there are junctions where the current either —– or rejoins the total current going into a junction has to —— the total current leaving it
If two identical components are connected in parallel than the same ——– will flow through each ————-
pd
same
current
component
safety design on plug
a fuse is connected between live pin and live wire the fuse wire melts it too much current passes through it . This means that the live wire is cut off
what happens if the live wire touches the nuetral wire
a very large current will rush between both wires this is called a short circuit if the fuse(A glass or ceramic canister containing a thin wire that melts if the current gets too high) breaks it will blow the circuit
nano watt
0.00 000 0001
micro watt
0.00 0001
milli watt
0.001
mega watt
1 000 000
gigga watt
1 000 000 000
power equation
power in watts= energy in joules divide / time in seconds
power in watts=
you can also found power if you don’t know the potential difference
potential difference (V) * current in amps
p= i squared r
where i is current r is resistance and p is power
The national grid uses a :
why is this :
Pylon cables made of
high pd and a low current
to transmit the high amount of power needed you either need a high pd or high current
the problem with high current is that you lose loads of energy as the wires heat up and energy is transferred to the thermal energy store of the surroundings. Its much cheaper to boost the pd up really high (to 400 000 V) and keep current relatively low
for a given power increasing the pd decreases the current which decreases the energy lost by heating the wires and the surroundings. this males the national grid an efficient way of transferring energy
very thick aluminium
what is the journey of electricity from power station to your home
power station , step up transformer(the pd is increased, cables and pylons(with huge insulators), step down transformer, home
transmitting eletricity at high voltage does what?
the total energy transferred by an appliance depends on :
the power of an apliance is the the energy it transfers per ——
it reduces energy loss and makes the system more efficient.
how long its been on for and its power
second
does what?
step up transformer
increases the voltage decreases the current
more turns on secondary coil
step-down transformer
decreases the voltage
increases the current
less turns on secondary coil
how can an object become negtive or positively charged
by gaining or losing electrons
positive ions are
and negatives are
cations
anions
(detailed)
what happens when two oppositionally charged objects move closer together
When 2 oppositely charged objects come close together this can cause electrons in the air molecules to be pulled towards to + object . If the
f ield is strong enough it can pull the electrons out of the air molecules. This flow of charge between the two charged objects can result in a spark.
why does balloon trick work
hair has negative charge
wall has negative charge
how does van da graff work
touchin vandegraf allows liek charges to build up on dome and on you cuz as we now like charges repel
how do nuetral objects become positively charged
A neutral object can become positively charged when electrons get transferred to another object (see Figure 2). Figure 2. Positively charging a neutral object by transferring electrons to a positively charged object.
not needed skip
led vs halogen bulbs
Halogen bulbs, while lasting longer than incandescent bulbs, only last up to 2,000 hours. In contrast, LED bulbs can last up to 25,000 hours, and LED tubes are rated for up to 50,000 hours. LED bulbs can use as much as 80% percent less energy than halogen bulbs.
what is a fuse and what is its job?
A glass or ceramic canister containing a thin wire that melts if the current gets too high
difference between Voltage and current
: Voltage is the force that makes electrons flow. It’s a difference in potential energy between two different points in a circuit. Current: Current is the rate of the flow of electrons. It’s measured in amperes, which are also called amps.
when an electrical charge goes through a —— in potential difference energy is transferred
Energy is supplied to the charge at the ——— to ‘raise’ it through a potential
The charge gives up this energy when it ‘—-‘ through any potential drop in components elsewhere in the circuit.
The formula is really simple
change
power source
falls
energy transferred (J)=
charge flow (C) * Potential difference (V)
what type of objects have electric fields?
electrically charged objects
pages in cgp workbook
43- I-V characteristics
