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Electricity powers almost everything in our daily lives, from charging your phone to lighting up the cities. But behind this everyday conveniences lie a set of powerful physics concepts that every student needs to understand.
In this blog, we’ll break down the topic of current of electricity into simple ideas. Instead of memorising formulas blindly, you’ll learn how everything connects, from current and voltage to resistance and Ohm’s Law.
An electrical circuit is a closed loop that allows charges to move through it. Without a complete loop, electricity simply cannot flow.
A basic circuit consists of three main parts:
Electric current is the rate of flow of charge.
This means how much charge passes through a point every second.
Where:
Current is not “electricity moving”, it is charges (electrons) flowing through a conductor. Electrons move from negative to positive terminal.
Historically, scientists assumed current flowed from positive to negative before electrons were discovered. Even after discovering the truth, the original convention remained.
Conventional current | Electron flow |
from positive → negative | from negative → positive |
One of the most important formulas in this topic is:
Where:
For example, if a current of 2 A flows for 60 seconds,
This means 120 coulombs of charge passed through the circuit.
Electromotive force (e.m.f.) is not a force. It is the energy supplied per unit charge by a source (like a battery).
Where:
If a battery has an e.m.f. of 1 V, it gives 1 joule of energy per coulomb of charge.
So, e.m.f. tells you how much energy the battery provides to move charges around the entire circuit.
While e.m.f. is energy supplied, potential difference (p.d.) is the energy used. It is the work done per unit charge across a component.
For example:
A light bulb converts electrical energy into light and heat, the voltage across it tells you how much energy is used per charge.
E.M.F | Potential difference |
Energy supplied | Energy used |
Across energy source (battery) | Across components (Eg: bulb, resistor) |
Drives current around circuit | Converts energy into other forms |
Resistance is what makes electricity less “smooth.” It is the measure of how difficult it is for current to flow.
Where:
Why Does Resistance Occur?
As electrons move through a conductor, they collide with atoms, these collisions convert electrical energy into heat. So, more collisions equals to higher resistance.
Factors Affecting Resistance
Resistance depends on several factors, let’s look at some of them.
1. Length of Wire
2. Cross-Sectional Area
3. Material (Resistivity)
Different materials resist current differently. This property is called resistivity (ρ).
The relationship is:
4. Effect of Temperature
Temperature plays a huge role in resistance. Higher temperature equals higher resistance.
This is because, atoms vibrate more and more collisions with electrons.
Ohm’s Law states that current is directly proportional to voltage, provided temperature is constant.
What this means is that when voltage increases, current increases where resistance stays constant.
These are some misconceptions made by many students.
❌ “Current flows from negative to positive in diagrams”
✔ Diagrams use conventional current (positive → negative)
❌ “Resistance and resistivity are the same”
✔ Resistivity = material property
✔ Resistance = depends on material + shape
In conclusion, the topic of current of electricity is not just about equations, it’s about understanding how energy flows and transforms.
Test yourself these concepts to know if you have truly understood Electrcity.
1. How electrons move
2. How energy is transferred
3. How resistance affects flow.
What this means is that when voltage increases, current increases where resistance stays constant.
All the best for your Physics O Levels! Happy Studying!
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