What is electricity ?

Ohm's Law is a fundamental concept in electricity that describes the relationship between three key components of an electrical circuit: voltage (V), current (I), and resistance (R). It states that:
V = I × R

I is the current in amperes (A)
V is the voltage in volts (V)
R is the resistance in ohms (Ω)


Ohm law states that at a constant temperature, the current (I) flowing through the resistor is directly proportional to the voltage or potential difference (V) applied across the resistor

If you increase the voltage applied to a circuit while keeping the resistance constant, the current will increase. Conversely, if you increase the resistance while keeping the voltage constant, the current will decrease.

How to connect a LED ?

The shorter terminal which is the cathode goes to the negative supply input, while the longer terminal which is the anode pin of the LED is connected with the positive input of the coin cell battery through the limiting resistor.

Why do we use a resistor ?

Although an LED is a diode, it's highly sensitive to current, and cannot tolerate anything exceeding its specified range. In order to ensure that an LED is safe from an over-current situation, a calculated resistor is normally added in series with one of the terminals of the LED. This resistor may be connected in series with either the cathode terminal or the anode terminal of the LED. This current limiting resistor can be simply calculated using the following formula: R = Input Supply - LED Voltage rating / LED max current. For example let's say an LED has a forward voltage rating of 3.3 V, and max current limit of 20 mA (0.02 Amps), then assuming the input supply is 6 V, the value of the series limiting resistor can be calculated as follows: R = 6 - 3.3 / 0.02 = 135 ohms, the nearest safe available value being 150 ohms.

How to calculate a resistor ?

What is the tolerance of a resistor?