Electricity Notes

What is Electricity?

Electricity is a basic form of energy that's super important in today's world. We use it every day to power our devices and make our lives easier.
Think of electricity as a flow of tiny particles called electrons moving through a wire or circuit.
Here are some examples of how we use electricity:
- Motion/Power: Electricity makes things move, like drills, computers, and cars.
- Heating/Cooling: We use electricity to heat up ovens and cool down refrigerators.
- Communication: Electricity helps us talk to each other through radios, phones, and the internet.
- Light: Electricity lights up our homes and streets with lamps and screens.

What is Electricity? (Continued)

Electricity flows in a loop called a circuit, where electrons move from a power source, through different parts, and back to the source.
A scientist named William Gilbert figured out a lot about electricity by studying magnets and static electricity.
Electrons are tiny particles with a negative charge, and they move when there's an electric force.
A battery helps push the electrons through a circuit, like making water flow through a pipe.

Conductors

Conductors are materials that let electricity flow easily through them.
They have "free electrons" that can move around and carry electricity.
Metals like copper, silver, and aluminum are great conductors and are used in wires and electronics.
Graphite, which is not a metal, can also conduct electricity because of its special structure.

Insulators

Insulators are materials that stop electricity from flowing through them.
They don't have free electrons, so electricity can't move.
Non-metals like rubber, plastic, glass, and ceramic are good insulators and are used to protect us from electric shock.

Electric Current

Electric current is how much electricity is flowing through a material, like copper or iron.
A device called a cell or battery pushes the electrons, creating the current.

Electric Current and Circuit

Use These formulas to calculate current:

$I = \frac{Q}{t}$

$Q = It$

The unit for measuring electric charge is the coulomb (C).
- One coulomb is a huge amount of charge, about $6 \times 10^{18}$ electrons.
- One electron has a tiny charge of $1.6 \times 10^{-19}$ C.
We measure electric current in amperes (A), named after a scientist named André-Marie Ampère.
A basic electric circuit has:
- A cell or battery to provide power.
- A light bulb to use the electricity.
- An ammeter to measure the current.
- A switch to turn the circuit on and off.

Electric Current and Circuit (Continued)

One ampere is like saying one coulomb of charge flows by every second.

$ 1 A = \frac{1 C}{1 s} $

We often use smaller units for current:
- milliampere ( $1 mA = 10^{-3} A$ )
- microampere ( $1 \mu A = 10^{-6} A$ ).
An ammeter measures the electric current in a circuit, and we connect it in series so all the current flows through it.

Problem: Electric Charge Calculation

If a light bulb uses 0.5 A of current for 10 minutes, how much electric charge flows through it?

Solution: Electric Charge Calculation

We know:
- $I = 0.5 A$
- $t = 10 \text{ min} = 600 s$
Use the formula:

$Q = It$

Calculate:

$Q = 0.5 A \times 600 s = 300 C$

Flow of Charges Inside a Wire

Inside a wire, electrons can move easily, even though atoms are packed together.
When current flows, electrons move slowly, but the effect of electricity spreads quickly.
A light bulb turns on fast because the electric force spreads quickly, not because electrons move super fast.

Electric Potential and Potential Difference

Electrons need a push to move through a wire, and that push is called potential difference.
A battery creates this potential difference, even when the circuit is off.
When we connect a battery, it pushes the electrons and creates an electric current.

Electric Potential and Potential Difference (Continued)

Electric potential difference is like the energy needed to move a charge from one place to another.
Use this formula:

Potential difference (V) = Work done (W) / Charge (Q)

$V = \frac{W}{Q}$

We measure potential difference in volts (V), named after Alessandro Volta, who invented an early battery.

Problem: Work Done Calculation

How much work do we need to do to move 2 C of charge across two points with a potential difference of 12 V?

Electric potential and potential difference (Continued)

One volt means we need one joule of energy to move one coulomb of charge.

$ 1 \text{ volt} = \frac{1 \text{ joule}}{1 \text{ coulomb}} $

$1 V = 1 JC^{-1}$

A voltmeter measures potential difference, and we connect it in parallel to the circuit.

Solution: Work Done Calculation

We know:
- Charge, $Q = 2 C$
- Potential difference, $V = 12 V$
Use the formula:
- Work, $W = VQ$
Calculate:
- $W = 12 V \times 2 C = 24 J$

Resistance

Resistance is how much a material stops electricity from flowing through it.
Other words for resistance are impede, slow down, obstruct, oppose, challenge, hinder, and resist.

Resistance (Continued)

In a circuit, resistance affects how much current flows and how much power is used.
Materials with high resistance:
- Glass and plastic have high resistance because their electrons can't move easily.
Materials with low resistance:
- Silver and copper have low resistance because their electrons can move easily.

Resistance and Ohm's Law

Resistance is measured in Ohms ( $\Omega$ ), named after Georg Simon Ohm.
Ohm's Law Equation:

$R = \frac{V}{I}$

Where:

$R$ is Resistance in Ohms ( $\Omega$ ).
$V$ is Voltage in Volts (V).
$I$ is Current in Amperes (A).

Resistance - Ohm's Law (Re-arranged)

Re-arranging Ohm's Law:
- $V = R \times I$
- $I = \frac{V}{R}$
If resistance is constant, voltage and current increase together.
Current is directly related to voltage if temperature and other conditions stay the same.

What Affects Resistance?

Factors affecting resistance include:
1. Cross-sectional Area:
  - Thinner wires have higher resistance because electrons have less space to move.
2. Length of the Material:
  - Longer wires have higher resistance because electrons encounter more friction.
3. Temperature:
  - Hotter materials have higher resistance because atoms vibrate more, making it harder for electrons to move.

Types of Resistors

Two main types of resistors:
- Fixed Resistors
- Variable Resistors

Fixed Value Resistor

Fixed value resistors have a set resistance that doesn't change.

Variable Resistor / Potentiometer

Variable resistors can be adjusted to change the resistance.

Ohm's Law

Ohm's law resource: https://quizizz.com/admin/quiz/6629f2f35f423a0ff4b37606/ohms-law

Extra Information: Conventional Current

Conventional current is the flow of positive charge, which is opposite to the direction of electron flow.
Electrons flow from the negative to the positive terminal.

Conventional vs Electron Current

Electrons flow from negative to positive.
Conventional current flows from positive to negative.

Direct & Alternating Current

Two types of current:
- Direct current (d.c.)
- Alternating current (a.c.)

Direct Current (d.c.)

Direct current (d.c.) flows in one direction.
It's like a steady stream of electrons moving from positive to negative.
Batteries produce direct current.

Alternating Current (a.c.)

Alternating current (a.c.) changes direction back and forth.
The terminals switch from positive to negative, creating a wave-like pattern.
Mains electricity is alternating current.
The frequency of a.c. is how many times it changes direction per second, measured in hertz (Hz).
In the UK, it's 50 Hz and 230 V, while in the US, it's 60 Hz and 120 V.

Direct Current (D.C.) Graph

A graph shows the current is constant over time, represented as a straight horizontal line.

Alternating Current (A.C.) Graph

A graph shows the current sinusoidal changes over time.

Direct Current vs. Alternating Current Table

Direct current (d.c.)

continuous and in one direction
produced by cells and batteries
involves a positive and negative terminal

Alternating current (a.c.)

constantly changing direction
produced by electrical generators i.e. mains electricity
involves two identical terminals

I-V graphs

Linear I-V graphs are straight lines through the origin, indicating a constant resistance. Non-linear I-V graphs are curved, indicating a variable resistance

Components with linear I-V graphs (ohmic resistors) include:

fixed resistors (at constant temperature)
wires (at constant temperature)

Components with non-linear I-V graphs (non-ohmic resistors) include:

filament lamps
diodes
LDRs
thermistors

Common Symbols

An electric cell:
A battery or a combination of cells:
Plug key or switch (open):
Plug key or switch (closed):
A wire joint:
Wires crossing without joining:
Electric bulb
A resistor of resistance $\text{R}$
Variable resistance or rheostat
Ammeter
Voltmeter

What is D.C Current?

Moves in One Direction
Never Comes Back

DIRECTED CURRENT?

Electron moves in One Direction.
Current that moves in One Direction is called D.C.

What is A.C Current?

INDIRECTED CURRENT

Current Reverse Direction
Current that moves in Both Directions is called A.C.

What is Polarity?

D.C CURRENT

Bulb
One Direction

A.C CURRENT

NO POLARITY
Polarity Changes
Reverse Direction

Frequency

TWO Directions
Cycles?
1 Cycle?
1 sec
50 cycles
50 Hertz
100 Times
220 Volt
Energy Needed

Parallel & Series Circuit

Parallel circuit
Series circuit

SERIES CIRCUITS

Shared amongst components

$ V{\text{total}} = V1 + V2 + V3$

The current is constant in all parts

$ I{\text{total}} = I1 = I2 = I3$

Total resistance is the sum of the individual resistances of components

$ R{\text{total}} = R1 + R2 + R3$

PARALLEL CIRCUITS

All components get the full voltage

$ V{\text{total}} = V1 = V2 = V3$

The current is split between branches based on resistance

$ I{\text{total}} = I1 + I2 + I3$

Reciprocal of total resistance is the sum of the reciprocals of the individual resistances

$ \frac{1}{R{\text{total}}} = \frac{1}{R1} + \frac{1}{R2} + \frac{1}{R3} $

Okay, here are more application-based practice questions on electricity:

Mobile Phone Charger: A mobile phone charger is rated at 5V and 2A. How much power does it consume, and what is the energy consumption if you charge the phone for 2 hours?
Extension Cord Safety: You have a 16 AWG extension cord rated for 13 amps. Can you safely power a space heater that draws 1200W on a 120V circuit with this extension cord?
LED Lighting Efficiency: You replace a 60W incandescent bulb with a 10W LED bulb that provides the same amount of light. How much energy do you save in a month if the light is used for 4 hours per day, and what is the percentage reduction in power consumption?
Electric Vehicle Charging: An electric vehicle has a 70 kWh battery. If you charge it with a 240V, 30A charger, how long will it take to fully charge the battery from 20% to