Electricity

charge, electrical potential

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 or wire

conventional current + the energy that they carry

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

, and when they 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, units and its rules for flowing

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

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

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

series 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 cannot draw a single line through all the components without leaving a gap or doubling back

current in series and parallel 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

and when returning 0V bc all E is transferred , even if no components - transferred to the wire 

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 (consider battery power)

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 be drawn.

therefore effect of total overall resistance is lower.

however more current means that battery takes up more energy as there is greater power

ohms law of resistance + total current equation

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

VIR circuit application

V = IR for an Ohmic conductor - temp K

where V is the voltage, PD that is the energy carried and transferred to a component per unit charge - battery PD - driving force of the charge in the circuit

I - current , charge flow rate measured in A, dependent on the driving force of the cell over the R - opposition to the flow of electrical charge

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 and their iv graphs

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 fillament in 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 and Light dependent resistor

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

resistance of the LDR decreases as the light in increases

core practical

Vary the voltage across the component by changing the resistance of the variable resistor, using a wide range of voltages (between 8-10 readings). Check the appropriate voltage reading on the voltmeter

For each voltage, record the value of the current from the ammeter 3 times and calculate the average current

Increase the voltage further in steps of 0.5 V and repeat steps 2 and 3

Make sure to switch off the circuit in between readings to prevent heating of the component and wires

Reverse the terminals of the power supply and take readings for the negative voltage (and therefore negative current)

Replace the fixed resistor with the filament lamp and repeat the experiment from step 1