GCSE Physics 06 — Electricity
PublicTopics include Electric Current and Charge, Potential Difference (Voltage), Resistance and Ohm's Law, Factors Affecting Resistance, I-V Characteristics, Sensing Circuits (Thermistors and LDRs), Series Circuits, and Parallel Circuits.
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Electric Current and Charge
Electric current is the rate of flow of charge, carried by electrons in metals.
Key points
- Current ($I$): The rate of flow of charge, measured in Amperes (A).
- Charge ($Q$): A property of matter, measured in Coulombs (C).
- Charge Equation: $Q = I \times t$.
- Charge Carriers: In metallic conductors, current is the flow of negatively charged delocalised electrons.
- Conventions: Conventional current flows Positive $\rightarrow$ Negative. Electron flow is Negative $\rightarrow$ Positive.
Worked example
Question
A current of 250 mA flows through a circuit for 3 minutes. Calculate the total charge transferred.
Solution
1. Convert units to standard SI units:
$I = 250 \text{ mA} = 0.25 \text{ A}$
$t = 3 \text{ minutes} = 3 \times 60 = 180 \text{ s}$
2. State the equation:
$Q = I \times t$
3. Substitute and solve:
$Q = 0.25 \times 180 = 45 \text{ C}$
4. The total charge transferred is 45 Coulombs.
$I = 250 \text{ mA} = 0.25 \text{ A}$
$t = 3 \text{ minutes} = 3 \times 60 = 180 \text{ s}$
2. State the equation:
$Q = I \times t$
3. Substitute and solve:
$Q = 0.25 \times 180 = 45 \text{ C}$
4. The total charge transferred is 45 Coulombs.
Common pitfalls
- Forgetting to convert minutes to seconds or milliamperes to Amperes.
- Thinking current is 'used up' by components (it is conserved).
Prerequisites
- Basic algebra (rearranging equations)
- Standard units of time
Further resources
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Electric Current and Charge
Clear diagrams comparing electron flow and conventional current.