Electrical Current and Circuits
This section explores the fundamentals of electrical current and circuit types, essential for understanding GCSE Physics electricity.
Electrical Current
Electrical current is defined as the flow of electrical charge. The relationship between current, charge, and time is expressed by the equation Q=IT, where Q is charge in coulombs, I is current, and T is time.
Highlight: In series circuits, current remains constant at any point, while potential difference is shared. In parallel circuits, current is shared, but potential difference remains the same across branches.
Circuit Types
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Series Circuits:
- Closed circuit with a single path for current
- Current is constant throughout
- Potential difference is shared among components
- Total resistance is the sum of individual component resistances
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Parallel Circuits:
- Branched circuit with multiple paths for current
- Current splits into different branches
- Potential difference is the same across each branch
- Total resistance is calculated using the reciprocal method
Example: In a series circuit with two resistors (R1 and R2), the total resistance is R_total = R1 + R2. In a parallel circuit, it would be 1/R_total = 1/R1 + 1/R2.
Electrical Charge
For charge to flow in a circuit, two conditions must be met:
- The circuit must be closed
- There must be a source of potential difference (e.g., a battery or cell)
Vocabulary: Coulomb (C) - The unit of electrical charge. One coulomb contains 6.24 x 10^18 electrons.
Resistance and Component Behavior
The relationship between current, resistance, and potential difference is governed by Ohm's Law: V = IR.
Definition: An ohmic conductor is a component with constant resistance, resulting in a linear relationship between current and potential difference.
Non-ohmic components, such as lamps, diodes, thermistors, and LDRs, have varying resistance depending on conditions like temperature or light intensity.
Example: In a filament lamp, resistance increases as the temperature of the filament rises, leading to a non-linear current-voltage relationship.