AC and DC

Type	Full form	Basic idea	Common example
AC	Alternating Current	Current changes direction periodically	Home electricity
DC	Direct Current	Current flows in one direction	Battery, power bank

AC

Used in homes and buildings.
In India, household supply is typically 230 V, 50 Hz AC.
AC can be dangerous and can cause serious electric shock.

DC

Batteries provide DC.
Examples: 1.5 V AA battery, 12 V battery, 5 V USB supply.
Electronics such as Arduino boards and many LED circuits generally use DC.

2. Voltage, Current and Resistance

Think of electricity like water flowing through a pipe:

Voltage (V) → electrical pressure
Current (A) → amount of electrical flow
Resistance (Ω) → opposition to current flow

The basic relationship is Ohm’s Law:

V = I × R

So:

I = V / R
R = V / I

Example

If you connect a 10 Ω resistor to a 5 V DC supply:

I = 5 / 10 = 0.5 A

So the current is 0.5 A.

3. Basic Circuit

A simple circuit needs:

Power source → wire → load → wire → back to power source

For example:

      + ────────[ SWITCH ]────[ LAMP ]───── +
     |                                      |
     |              BATTERY                 |
     └──────────────────────────────────────┘

If the switch is closed, current can flow and the lamp turns on.

If the switch is open, the circuit is broken and the lamp turns off.

4. Common Electrical Components

🔋 Battery

Provides DC electrical energy.

💡 LED

Produces light when current flows through it.

Important: An LED normally needs a current-limiting resistor.

⏚ Resistor

Limits current.

Common values:

220 Ω
330 Ω
1 kΩ
10 kΩ

🔘 Switch

Opens or closes a circuit.

⚡ Capacitor

Stores electrical charge temporarily.

🧲 Inductor

Stores energy in a magnetic field.

🔌 Diode

Normally allows current to flow primarily in one direction.

🔧 Fuse

Protects a circuit by opening when excessive current flows.

5. Basic Wire Colour Codes

Wire colours depend on the country, wiring standard, and type of installation. Don’t identify a live wire by colour alone.

For modern IEC-style AC wiring, commonly encountered colours are:

Wire	Common colour	Purpose
Live / Line (L)	Brown	Carries supply voltage
Neutral (N)	Blue	Return conductor
Earth / Protective Earth (PE)	Green/Yellow	Safety connection

In DC circuits

There is no universal requirement that every DC circuit use the same colours, but a very common convention is:

DC connection	Common colour
Positive (+)	Red
Negative (−)	Black

Other equipment may use different colours, so always check the circuit diagram or manufacturer’s markings.

6. Resistor Colour Code

Resistors often have coloured bands that indicate their resistance.

For the first two bands:

Colour	Number
Black	0
Brown	1
Red	2
Orange	3
Yellow	4
Green	5
Blue	6
Violet	7
Grey	8
White	9

Example: Brown – Black – Red

Brown = 1
Black = 0
Red = ×100

So:

10 × 100 = 1000 Ω = 1 kΩ

For a typical 4-band resistor:

Band 1 = first digit
Band 2 = second digit
Band 3 = multiplier
Band 4 = tolerance

Common tolerance colours:

Gold = ±5%
Silver = ±10%

7. Series and Parallel Circuits

Series

+ ──[R1]──[R2]──[R3]── -

The same current flows through each component.

For resistors:

Rtotal = R1 + R2 + R3

Example:

10 Ω + 20 Ω + 30 Ω = 60 Ω

Parallel

       ┌──[R1]──┐
+ ─────┤        ├──── -
       ├──[R2]──┤
       └──[R3]──┘

The voltage across each parallel branch is the same.

For two resistors:

1/Rtotal = 1/R1 + 1/R2

8. Power

Electrical power tells you how much electrical energy is being used per unit time.

P = V × I

Where:

P = power in watts (W)
V = voltage in volts (V)
I = current in amperes (A)

Example:

A device operating at 12 V and drawing 2 A:

P = 12 × 2 = 24 W

So its power is 24 watts.

9. AC vs DC — Quick Comparison

                 ELECTRICITY
                     │
          ┌──────────┴──────────┐
          │                     │
         AC                    DC
   Alternating Current    Direct Current
          │                     │
     Home supply             Battery
     230 V, 50 Hz            1.5 V, 5 V,
     in India                9 V, 12 V etc.

10. Very Important Safety

Basic Electric