Introduction to electricity and electronics
Safety Precautions
● Inform your teacher or school staff immediately when you become aware of a safety hazard
● Always inform your teacher when you're injured in the shop
● Do not underestimate the potential danger of a 220V circuit
● Do not work on a live circuit unless ABSOULTELY NECESSARY and under supervision of tutor/lecturer.
● Stand on dry, non-conductive surfaces when working on live circuits.
● Never bypass an electrical protective device unless there's proper instruction and supervision
● If you have a hot soldering iron on your bench, arrange your work so that you never have to reach over it.
● Keep your work area clean
● Always wear safety glasses/goggles when you are operating any kind of power tool or when soldering.
● Know where the fire extinguisher is and know how to use it.
● Never take a shock on purpose.
● Do not open or close any main switch without permission of teacher, unless there's emergency
● Do not turn on the power if you're not sure if the circuit is properly connected.
● Make sure all electrical connections are secure before applying a voltage
● Always use properly grounded tools, User only those tools with three pronged plugs or double insulated tools with two pronged plugs
● Keep your hands dry when working on electronics
● Do not eat/drink while soldering, some solder/circuit board contains lead which is poisonous, you may not die instantly but you become STUPID
● Voltage above 30V is considered dangerous
● Any current flow above 0.005A/5mA is considered dangerous
● A common 1.5V dry cell could output as much as 2.5A
● Conclusion: you can kill yourself with a dry cell! (Under optimal conditions)
● Darwin awards: http://www.darwinawards.com/darwin/darwin1999-50.html
Structure of matter
Matter->Molecules->Single atoms ->Sub-atomic particles
Structure of an atom
Atom consists of 2 main parts and at least 3 core sub-atomic particles
-Core: dense central part made up of neurons (neutral) and protons (positively charged)
-Orbital parts: Made up of electrons (negatively charged) that orbit around the core on different energy levels (shells)
Charge and electrons
Atoms that gain extra electron(s) will be negatively charged.
Atoms that lose electron(s) will be positively charged.
And that’s how the + and - signs that often appears in circuit comes from.
Atoms with charges are called IONS
Definition for "electricity"
Electricity is defined as the flow of electrons
Conductor and insulator
Common conductor: Gold, silver, copper, zinc, brass, platinum, tin, lead, tungsten...
The atomic structure of metals allow electrons to flow freely, thus they are good conductor for electricity.
Static electricity- electrical charge in static
Testing for static charge using Aluminum Leaf Electroscope
Current electricity- electrical charge in motion
Electric circuit
Electric circuit works in the similar way as cycles appear in nature (e.g. water cycle, carbon cycle...etc)
Fruit power
Connect few juicy fruit together with copper wire and galvanize nails, it can generate enough electricity to light up an LED.
What actually generated electricity in the fruit circuit?
Since copper and zinc (from the galvanized nails) have different tendency for losing electrons, it creates a potential differences for electrons to flow to a unified direction, the acidic environment provided by the fruit facilitate such ion/electrons movement, generate a weak electricity which is strong enough to light up the LED
Terms
Current (I)
The rate of flow of electrons through a conductor is called current (identified using symbol I). The unit for current is amperes (A). One ampere is a coulomb of charge pasting a given point in a second.
I=V/R
Consider current as the volume of water passing though a section of water pipe at specific time
Voltage (V)
Voltage is the difference of potential energey that forces electrons to flow in a circuit. The unit for voltage is volts (V).
V=IR
Consider voltage as the speed of water flowing through the water pipe
Resistance (R)
Resistance is the opposition to the flow of electrons. Resistance is measured in ohms (Ω).
R=V/I
Consider resistance as the friction/blocking of dirts in a water pipe
The relationship between voltage, current and resistance are describe by the famous Ohm's law
V=IR
Power and energy
In everyday language, power and energy are usually use in the similar way.
In fact they are two different concepts.
Power (P)
Power refers to the amount of energy convert from one form to another in a certain period of time.
In terms of electricity, it means the amount of electrical energy being converted to other forms of energy such as sound, heat or kinetic energy.
P=VI
Energy (E)
When measuring energy, we use the unit “Joules”. It equals to the work done by a force of one newton traveling through a distance of one meter
What kind of movement are we measuring when we talk about electricity then?
E=VIt
E is the energy in joules
V is the voltage in volts
I is the current in amperes
t is the time in seconds
Current flow and electron flow
The direction of electron flow and current flow are opposite to each other
Current flows from the positive pole to the negative pole, you can consider this as the motion of ions.
Direction of electron flow is from the negative pole to positive pole.
Current flow from positive pole to negative pole, while electrons flow from negative to positive flow (remember electrons are negatively charged, thus they are attracted by the positive pole)
