Electrical CircuitsOxford AQA IGCSE Physics: Flashcards
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Why do metals conduct electricity easily?
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- Why do metals conduct electricity easily?
- They contain free electrons that are not bound to a particular atom and can drift through the metal lattice.
- Define current and give its equation.
- Current is the rate of flow of charge: I = Q/t (current in amps, charge in coulombs, time in seconds).
- Define the potential difference across a component.
- The energy transferred per unit charge as charge passes through the component: V = E/Q.
- What is static electricity and how is it removed?
- An imbalance of charge on an object with no conducting route away; it is removed by discharge, e.g. a spark or lightning.
- State Ohm's Law.
- For a resistor at constant temperature, current is directly proportional to potential difference (V = IR gives a straight-line I-V graph through the origin).
- How does a filament lamp's resistance change with temperature, and what does its I-V graph look like?
- Resistance increases as temperature increases, so the I-V graph curves and flattens as pd increases.
- How does a thermistor's resistance change with temperature?
- Its resistance decreases as temperature increases.
- How does an LDR's resistance change with light intensity?
- Its resistance decreases as light intensity increases.
- Describe the resistance of a diode in the forward and reverse direction.
- Forward resistance is low (current flows easily); reverse resistance is very high (almost no current flows).
- What is special about an LED compared with other forms of lighting?
- It emits light only when current flows in the forward direction, and uses much less current for a similar brightness.
- Give the three rules for a series circuit.
- Combined resistance is the sum of individual resistances; current is the same everywhere; total pd is shared between components.
- Give the three rules for a parallel circuit.
- Combined resistance is less than any individual resistance; current splits between branches; pd across each branch is the same.
- Why does a resistor heat up when current flows through it?
- Moving charges collide with the stationary atoms of the resistor, transferring energy and causing heating.
- Name two circuit components whose resistance is not constant.
- Any two of: filament lamp, diode, thermistor, LDR.