A 20 Ω resistor has 10 V applied across it. What is the current?
\[ I = \frac{V}{R} = \frac{10}{20} = 0.5 \, \text{A} \]
Even though his discoveries weren’t widely accepted at first, and called “a web a naked fantasy”, Georg Simon Ohm is now recognized as one of the main pillars for the understanding of electricity.
- Definition: rate at which electrical charge flows past a specific point.
\[ I = \frac{\Delta q}{\Delta t} \]
We use the letter \( I \) to represent it, and it is measured in amperes (A) using an instrument called ammeter.
- Definition: difference of electrical potential energy between two different points.
In the content of a circuit, voltage is what makes current flow, meaning it makes the electrons move. The generators produce it.
We use the letter \( V \) or \( \Delta V \) to represent it, and it is measured in volts (V) using an instrument called voltmeter.
You can also find it as potential difference, electric pressure, or electric tension.
- Definition: opposition to the flow of electric current.
High resistance means less current flows for the same voltage, while low resistance means more current flows.
We use the letter \( R \) to refer to it, and it’s measured in ohms (Ω) using an instrument called ohmmeter.
It states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them.
\[ I = \frac{V}{R} \]
Tip: to understand better how a circuit works, it’s useful to visualize it like a flow of water, as shown in the figure below.
| Intensity | Voltage | Resistance | |
|---|---|---|---|
| Representation | I | V | R |
| Units | Amperes (A) | Volts (V) | Ohms (Ω) |
| Instrument to measure it | Ammeter | Voltmeter | Ohmmeter |
It’s important to note that you can apply Ohm’s Law in the whole circuit, using the equivalent resistance, or in a specific resistance, battery, or other ohmic components.
A 20 Ω resistor has 10 V applied across it. What is the current?
\[ I = \frac{V}{R} = \frac{10}{20} = 0.5 \, \text{A} \]
A device operates at 12 V, but the maximum safe current is 0.2 A. What is the minimum resistance you must use to keep the current safe?
\[ R_{\text{min}} = \frac{V}{I_{\text{max}}} = \frac{12}{0.2} = 60 \, \Omega \]
Written by Sofia Osorio