Ohm’s Law
Ashraf Said Ahmad AlMadhoun · Maker Innovations Series · 2023
It is high time that we learn about a fundamental concept in circuit designing which is known as Ohm’s law. In this chapter we are going to discuss about its concept and its application to safely light up a LED. Figure 5-1 shows a simple circuit that will be used for demonstration purposes in this chapter, and it contains only four components, battery, resistor, LED, and a switch. You should know that electric current flows from the positive terminal of a power source, i.e., a battery, to the negative terminal completing its path. This is denoted by “I” and demonstrated by a dashed arrow in Figure 5-1, and we can the direction of the current as arrow is headed from the positive to negative terminal. Another important and related concept of electricity is voltage. When current flows through a component like LED or resistor, there is an associated change in potential energy across that component; this potential difference is known as voltage denoted by “V” in Figure 5-1. The amount of voltage drop across the component depends on its resistance which is simply the amount of the obstruction it causes in the flow of current. Resistance can be seen denoted as “R” in Figure 5-1. Resistance, although seems an unwanted quantity because it hinders the flow of current, plays a very important role in circuit theory. It makes sure that your electronic components do not fry because of the access current in the circuit. If you directly connect an LED with a battery, without a resistance in the circuit, your LED will be burnt away. So adding resistance into the circuit is crucial, but how much resistance should we add? What if we add a lot of resistance that only a few milliampere of current can flow through the circuit? Your LED will not glow then. Here is when Ohm’s law comes into play. It helps us to find the right combination of resistance, current, and voltage. It formally states that “the voltage across a conductor is directly proportional to the current flowing through it.” The mathematical expression of this law is given in Equation 5.1.