Electricity

charge,

a property of a body that experiences a force in an electric field (bundles of electrons that pose a bigger charge than a single electron)

electrical potential (the energy carried by a charge at a certain point in a circuit) - basically voltage at one single point

rules of charge

work done + conservation

charge in a circuit can never be used up or created as electrons cannot be created or destroyed so the coulombs of charge in a circuit do NOT change therefore the overall current in a circuit will never change

whenever charge flows through and electrical circuit, work is done as energy is transferred to the components

conventional current

electric current flows from the - to the + terminal of a battery, carrying energy inputted by the cell

, and when tey return to the + end they are carrying less energy than when they left the negative end.

However, when drawing we always draw it as if the current it going from the + to - terminal because that is convention

calculating charge flowed past a point in a circuit

Q=IT : Where Q is the charge flowed - measured in coulombs (C)

where I is current measured in amperes (A)

where T is time measured in seconds (s)

this means that one ampere is the current of one coulomb per second flowed

Current

the rate of flow of electric charge around a circuit (measured in amperes {A})

current will only flow through a component if there is a potential difference across that component \\ and only through a circuit if there is a potential difference across the battery (power source)

(potential difference of the power source provides the driving force for charge to flow around the circuit)

Generally speaking rules

higher p.d across a given component, higher current will be

higher resistance of a component, smaller the current that flows will be

parallel circuits

in a series circuit is where all the components are connected in a single loop and line between the + and - terminal of a battery (without leaving any gaps or doubling back)

parallel circuits

In a parallel circuit components are connected in different loops each with their own connection to the +- terminal of the power supply, branching off junctions in the circuit

you draw parallel when you you cannot draw a line through all the components without leaving a gap or doubling back

current in series circuits + junction rule

electric current has only one path to flow through in a series circuit but multiple paths/junctions in a parallel one,

this means that the current in parallel splits during a junction, depending on how much current the components in each loop take

in the 3 way junction rule , where I₃ is the first current, and it splits into I₂ and I₁ (I₁ + I₂ = I₃) always

Battery P.D and component P.D

P.D is how much energy is transferred per unit charge that passes between two points in a circuit

The voltage across a component is work done (energy transferred to the components) per unit charge in flowing through it

battery voltage

For current in a circuit, there must be a potential difference across the circuit (power supply), and in the components for charge to flow through them

the p.d of a battery is the energy inputted per unit charge

1 volt is defined to be the p.d. that will deliver 1J of energy when 1 coloumb of charge flows

electrical potential reference point 

(for reference electrical potential is how much energy the charge has at one point, therefore the difference measures it between two points to see how much is transferred)

VEQ equation

V = E/Q 

voltage (V) = energy transferred\work done (J) / Charge flowed (Q)

how much energy transferred to a component 

this means that 1 Volt is 1 Joule per coulomb

series voltage

In series because there is one loop, all the p.d from the battery is shared amongst the components in the circuit,

va - is psu voltage

series : Va = V1 + V2 + V3

Voltage parallel circuits 

however in parallel each junction/loop gets all of the battery’s p.d for each loop, and its own share of current, shared amongst its components 

when we have 3 identical resistors in series vs parallel (in their own diff junctions) off the power supply V_a

Parallel : Va = V1 = V2 = V3

Resistance in series parallel equations

I = V/R 

in series when more Ωs , the total Ω increases  ∴ current decreases

R_T  = R₁ + R₂ + R_{3 …} R_N,

However in parallel : 

1/R_T = 1/R₁ + 1/R₂ + 1/R₃ ….. 1/R_n

Explanation of parallel resistance

Each parallel loop receives its own share of current. R = V/I

That means in parallel each time when we add add a branch with a resisting component, we provide another path for the current to flow, that means for a set voltage a greater I from the batt. will ne drawn.

therefore effect of total overall resistance is lower.

however more current means that battery takes up more energy

ohms law of resistance

For some resistance at a constant temperature, the current through the resistor is proportional to the the p.d across it - for an ohmic resis{tor}(ting component)

V = IR

where temp is constant : V ∝ R

current is dependent on V and R

total current = whole cell voltage / combined component resistance

what resistance tells us bc it is …..

the p.d required to drive a current through a component

- as resistance is the measure of the opposition to the flow of electrical charge through a component or circuit

ohmic + non-ohmic resistors

A resistor that does not change resistance when varying the voltage across it - as long as the temperature is constant

if an IV graph of a component is curved, not straight it is non ohmic

why bulb is a non-ohmic resistor

because it increases resistance as voltage increases. This is because the bulb heats up and ions (atoms) in the metal filament vibrate more,

this causes more collisions between the electrons (like a barrier) making it harder for current to flow - collisions transfer Ψ

(same principle of voltage)

Thermistor

resistance of a thermistor decreases as the temperature increases (not linear)