Unit 6 - Electric Circuits

Electric Current
Electric current is the flow of electric charge

In a lightbulb light and heat are produced when electrons flow through the filament, and 'bump" into the atoms

Electric Circuit
An electric circuit is the path through which electrons flow

Electrons cannot flow through an open circuit (circuit is not connected)

Electrons can flow through an open circuit (circuit is connected)

In an electric circuit electrons move in a chain reaction, pushing the electrons in adjacent atoms forwards through the circuit

Formula
Electrons move quite slowly (mm/s) even though the effect of turning on a circuit happens very fast

Current is measured in amperes (A), the rate at which amperes flow through a certain point

1A=1C/s (1 ampere = 1 coulomb per second) (1 coulomb = 6.24x1018)

I=q/t (current = charge / time)

Mandatory Components
power source

conductors (wire)

load

Optional
switch

fuse - prevents to much current from flowing through - when too much current flows through the fuse melts creating an open circuit

Conventional vs Electron-Flow Current
NOTE: This is proof that IB is intentionally trying to screw with your mind by teaching you one thing but making you do another

Conventional current is more used in workplaces and by professors, it says that electrons flow from positive to negative, but it's WRONG

Electron-flow is less used however it is CORRECT as it says that electrons flow from negative to positive

NOTE: ON ALL IB EXAMS OR EVALUATIONS USE CONVENTIONAL

NOTE: If you are consistent you can use either option as they would both work

NOTE: The reason the majority of people use the wrong method is because it is the one that came first

AC and DC Current
DC - direct current - continuous flow of charge in one direction - battery

AC - alternating current - direction of current alternates back and forth but the energy flows like a wave - outlet

AC is used for large scale production because it is cheaper and easier to transmit over large distances

Calculating Voltage, Current and Resistance in Series and Parallel Circuits
NOTE: This section will consist of part from 6-1, 2 and 3

The formula V=IR (voltage = current x resistance) will be used quite often in this unit, so you better know it :)

Voltage
Voltage is what causes current to flow in a circuit

Look at voltage like water which always flows from higher gravitational potential energy to lower gravitational energy Voltage flows from higher electrical potential energy to lower potential energy

Batteries store chemicals that create different levels of electrical potential energy at the ends, this difference is called potential difference

Voltage is the work done per unit charge to move a small positive charge between two points

V=E/q (voltage = energy(work) / charge)

Resistance
Resistance is the force that opposes the flow of current

Resistance is measured in Ohms

R=pl/A (resistance (Ohms) = resistivity of material (Ohms x m) x length of material(m) / cross sectional area (m2))

If a circuit is broken the air will act as a resistor of infinite resistance thus stopping electron flow

Series Circuits
There are no junctions in a series circuit and the current has only one path to follow (if this explanation is not enough to explain to you what a series circuit looks like maybe you should do the unthinkable and google it)

A series circuit has the same current in all parts of the circuit

The sum of the voltages across all the loads in a series equals to the voltage across the battery

The V=IR formula can be used to calculate the resistance of each individual load

The total resistance of the circuit can be found by simply adding up the resistances

Parallel Circuits
In a parallel circuit there are multiple ways for electrons to get from one side of the power source to the other (once more google it if this information is not enough to paint an image)

The voltage across two branches that split at the same point and join at the same point is the same

The amperage at a point before a junction is the same as that where the branches meet

The total resistance within a single branch of a circuit can be calculated as you would a series circuit

The total resistance in a parallel circuit is:

((RTOTAL)-1=(RTOTAL OF BRANCH 1)-1+(RTOTAL OF BRANCH 2)-1+(RTOTAL OF BRANCH 3)-1+...+(RTOTAL OF BRANCH n)-1

Voltmeters
Voltmeters measure volts(potential difference)

Compares energy of electrons at two places in a circuit

Must be placed in parallel with the circuit

Ideal voltmeters have infinite resistance

A non-ideal voltmeter can be drawn with internal resistance in parallel with an ideal voltmeter

Ammeters
Measure current flowing through a circuit

Coulombs of electrons passing a point every second

Must be placed in series with a circuit

Ideal ammeters have zero resistance

A non-ideal ammeters can be drawn with internal resistance in series with an ideal ammeter

Power
NOTE: This is from 6-3

Power is measured in watts

P=IxV (Power = current x voltage)(my time is too precious to derive this and show you that it is infact true so then just simply go with it)

More branches in a circuit means more current is drawn, more current means more power, more power and the battery dies faster

Batteries
An ideal battery has no internal resistance

A non-ideal battery can be drawn with internal resistance in series with an ideal cell

Terminal Voltage the voltage across the end of the battery (VT). Terminal Voltage is higher when there are no loads attached

EMF the voltage of a battery without internal resistance (Vemf)

Vemf=Ix(Ri+Re) (EMF=current x (internal resistance + external resistance)

Vemf=IxRi+VT (EMF=current x internal resistance + terminal voltage)

Components
A battery has three components (cathode, anode, electrolyte)

Cathode - positive electrode - undergoes a reaction that produces positive ions

Anode - negative electrode - undergoes reaction that produces negative ions

Electrolyte - transports ions between the two side

Types of Batteries
Disposable - primary cells - alkaline batteries

Rechargeable - secondary cells - nickle-cadmium - lithium ion - lead acid

NOTE: In order to recharge a battery, a current must be sent opposite to the direction of travel when discharging the battery

Potentiometers
A potentiometer is a variable resistor

If the potentiometer is set at half then the its resistance would be half (I know mind blowing)