P4 and P5- Electrical Circuits Flashcards
what is the memory hack to remember the electrical equations
Can Jake Very Well Afford Chocolate Since Jake Went Away Often
what do the letters in the memory hack stand for
C - Coulombs = Charge (Q)
J - Joules = Energy (E)
V - Volts = Potential Difference/Voltage (V)
W - Watts = Power (P)
S - Seconds = Time (t)
A - Amperes = Current (I)
O - Ohms = Resistance (R)
what are all the equations of electricity
E=QV P=IV Q=It E=Pt V=IR
what is static electricity
Static electricity = with two insulators
what happens when 2 insulators are rubbed together
When two insulators are rubbed together, electrons move from to another, causing both materials to become charged, and so the two materials attract each other
what happens to charged objects
Charged objects create electric fields around themself
when drawing lines of fields which way do the arrows face for positive and negative charged objects
For positively charged objects, the arrows point outwards
For negatively charged objects, the arrows point inwards
The arrows must be perpendicular to the surface it is coming out from
Try to keep the arrows the same length
what is the electrical symbol for a cell
line where the left one is taller than the right one
what is the electrical symbol for a open switch
disconnected line with 2 dots
what is the electrical symbol for a closed switch
connected line with 2 dots
what is the electrical symbol for a bulb
a circle with a ‘x’ in it
what is the electrical symbol for a diode
a circle with the next symbol in it
what is the electrical symbol for a LED
circle with the next symbol in it with 2 arrows pointing out (out for emitting)
what is the electrical symbol for a Ammeter
a circle with an ‘A’ in it
what is the electrical symbol for a Voltmeter
a circle with a ‘V’ in it
what is the electrical symbol for a fixed resistor
a rectangle
what is the electrical symbol for a variable resistor
a rectangle with a line going diagonally through it
what is the electrical symbol for a fuse
a rectangle with a line going horizontally through it
full form of amps
Amps = Amperes
what does a diode do
Diode = only allows current through in one direction - only allows current through when connected with its terminals in a particular place
what does LED stand for
LED = light-emitting diode
what does a resistor do
Resistor controls the size of the current (fixed resistor only has one current setting)
what does a variable resistor do
Variable resistor - you can change the current size
define current
Current = the rate of flow of charge
definition of potential difference
Potential difference of a component = the energy transferred to the component, or the work done on it by each coulomb that passes through it
what are the 4 things needed for a current to work
4 things needed for a circuit to work:
power source
component
complete loop
no short circuit
what is a short circuit and how does it happen
Short circuit = a connection in the circuit that should not be there - a wire is connecting two different parts of the circuit that should have two different potential differences. Having this abnormal connection results in too much current flowing through which leads to overheating and even fires
draw a graph for a filament light bulb
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draw graph for ohmic conductor
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draw graph for diode
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what does thermister mean
Thermistor = temperature dependent resistor
If temperature increases, its resistances decreases.
how does current flow in series and parallel circuits
Current in:
A series circuit is equal
A parallel circuit is shared
how does potential difference (voltage) work in series and parallel circuits
Potential difference in:
A series circuit is shared
A parallel circuit is equal
how does resistance in series and parallel circuit work
Resistance in:
A series circuit: RT=R1+R2+R3+R4….
in a parallel circuit:1/RT = 1/R1 + 1/R2 + 1/R3 …
what happens to current in a series circuit
In a series circuit, the current remains the same at all points
what happens to p.d in series circuit
In a series circuit, the total p.d of the power supply is shared between the components
what happens to resistance in series circuit
In a series circuit, the total R is the sum of the resistance of each component (so you just add them up)
how does adding more resistance increase total resistance
Adding more resistance in series increases the total resistance as:
the pd is shared and so is less for each of them, and so the current is less than before (as we know current and pd are directly proportional). BUT, as the total pd is the same, the overall resistance is greater
how to find current in parallel circuits
In parallel circuits, the total current is the sum of the currents through the separate branches
what happens to p.d in parallel circuits
Pd for the components in parallel will be equal
how are resistance and current linked
The bigger the resistance of the component, the smaller the current through it
how does adding more resistors decrease the total resistance
Adding more resistors in parallel decreases the total resistance ⟶ pd is the same for each resistor, so adding resistor increases the current, decreasing the total resistance
what is DC current
Direct current (dc) is the current in a circuit that goes in one direction ONLY
what is AC current
Alternating current (ac) = repeatedly reverses in direction in successive cycles
what is AC currents frequency
Ac’s frequency = the number of cycles it passes through each second
what are the 3 wires in mains circuit
Every mains circuit has a live wire (brown), a neutral wire (blue), and an earth wire (green/yellow)
what is the pd between nuetral and live wire called
The pd between the neutral and live wire is called the pd of the live wire
why is live wire dangerous
Live wire is dangerous its pd repeatedly changing from + to - and back every cycle
where is electricity supplied for mians appliances
For mains appliances, electricity is supplied to homes and buildings from power stations through the National Grid
what is the national grid
National Grid = a nationwide network of cables and transformers
what is step up transformer and what do they do
Step-up transformers = used at power stations to transfer energy to the national grid
Step-up transformers increase the alternating pd making them much bigger
what are step down transformers used for
Step-down transformers are used to transfer electricity from the national grid to the consumers (houses, buildings etc)
If it’s starting and ending as low pd, why do we increase the pd for the journey?
If we increase potential difference, we make current lower to transfer the same amount of power (here we are thinking about P=IxV, so I and V are inversely proportional)
If we decrease the current, we are decreasing the resistance in the cables. Decreasing the resistance in the cables means we lose less power as heat loss due to resistance is less
define power
power = how quickly energy is being transferred
what is frequency
frequency = 1/time taken for one cycle
why do appliances have plastic cases and are double insulated
Appliances have plastic cases, and are double insulated for safety
plastic cases so electricity isnt conducted into the case and double insulated so elctricity isnt wasted
which path does earth wire take
The Earth wire: current takes the path of least resistance
where is the current in earth wire directed to
the earth wire is connected to the ground - if you ever come into contact with a live wire you won’t be electrocuted as the current will be directed into the ground instead, keeping you safe
which wire is the longest wire designed to make contact with
The longest pin on our plug is designed to make contacct with the earth wire first ⟶ when a metal case appliance is plugged in, it’s automatically earthed.
why do plugs have a fuse between live pin and wire
Plugs have a fuse between the live pin and wire ⟶ if there’s too much current, this will make the fuse melt and so it cut the live wire off
what is wire made of
The electrical wire is made of copper as it is a good conductor of electricity and it is ductile
what does short-circuit mean
A short circuit = when the live wire touches the neutral wire and a very big current passes between them at contact ⟶ the fuse melts cutting it off
Get two equations by incorporating V=IR into P=IV.
P=IV
P=Ix(V=IR)
P=IxIR
P=I^2R
P=IV
P=(I=V/R)xV
=V/RxV
=V^2/R
Q=It
what is the equation for power
Power (W) = Energy (J)/time (s)
In any appliances:
1. I = the rate of flow of charge
2. P.d. is the energy transferred to the it, by each coulomb of charge that passes through it
3. Power = the amount of energy transferred each second
why does a resistor become hotter
When charge flows through a resistor, energy is being transferred to it, so the resistor becomes hotter
how to calculate efficiency
efficiency = its output power/its input power x 100
