Introduction
When electric charges flow through a conductor (like a metallic wire), an electric current is said to flow.
Electric Circuit
An electric circuit is a continuous and closed path of electric current. A switch helps to make or break the circuit.
Electric Current
Electric current is the amount of charge flowing through a cross-section per unit time.
Formula for Electric Current
I = Q / t
SI Unit of Electric Current
The SI unit of charge is coulomb (C) and the SI unit of current is ampere (A). 1 A = 1 C / 1 s.
Ammeter
An ammeter measures current in a circuit and is always connected in series.
Example 11.1 - Problem
Problem: A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the total electric charge that flows through the circuit.
Step 1 - Write the given values
- Current, I = 0.5 A
- Time, t = 10 min = 600 s
Step 2 - Write the formula
Formula: Q = I × t
Step 3 - Substitute the values
Q = 0.5 × 600
Step 4 - Final Answer
Answer: Q = 300 C
Fun Fact - Number of Electrons
Fun Fact:
1 C ≈ 6 × 1018 electrons.
For 300 C, electrons = 300 × 6 × 1018 = 1.8 × 1021 electrons.
To compare: Earth's population ≈ 8 × 109 people.
If shared equally, each person on this planet would get about 225 billion electrons!