โก 11.1 Electric Current and Circuit
We are familiar with air current and water current. Similarly, if electric charge flows through a conductor (like a metallic wire), we say there is an electric current in the conductor.
I = Q/t
Where:
- I = Current (Amperes, A)
- Q = Charge (Coulombs, C)
- t = Time (Seconds, s)
Key Facts:
- 1 Coulomb = charge of 6 ร 10ยนโธ electrons
- 1 Ampere = 1 Coulomb/second
- Electron charge = -1.6 ร 10โปยนโน C
- Conventional current direction is opposite to electron flow
๐ 11.2 Electric Potential and Potential Difference
Charges don't flow in a copper wire by themselves, just as water in a horizontal tube doesn't flow. We need a potential difference to make charges move.
V = W/Q
Where:
- V = Potential Difference (Volts, V)
- W = Work Done (Joules, J)
- Q = Charge (Coulombs, C)
Key Facts:
- 1 Volt = 1 Joule/Coulomb
- Named after Alessandro Volta (1745-1827)
- Voltmeter measures potential difference
- Battery creates potential difference through chemical action
Example 11.1 - Solving with Animation
Problem: A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric charge that flows through the circuit.
Solution:
Given: I = 0.5 A, t = 10 min = 600 s
Formula: Q = I ร t
Q = 0.5 A ร 600 s
Answer: Q = 300 C
๐ก Watch the animation above to see how 300 coulombs of charge flows through the bulb filament over 10 minutes!
Practice Questions
- What does an electric circuit mean?
- Define the unit of current.
- Calculate the number of electrons constituting one coulomb of charge.
Answers:
1. A continuous and closed path of electric current
2. One ampere = flow of one coulomb of charge per second
3. Number of electrons = 1/(1.6 ร 10โปยนโน) = 6.25 ร 10ยนโธ electrons
| Quantity |
Symbol |
Unit |
Formula |
| Electric Current |
I |
Ampere (A) |
I = Q/t |
| Electric Charge |
Q |
Coulomb (C) |
Q = I ร t |
| Potential Difference |
V |
Volt (V) |
V = W/Q |
| Work Done |
W |
Joule (J) |
W = V ร Q |