Knowledge Organiser: I-V Characteristics
This topic summary covers Knowledge Organiser: I-V Characteristics within I-V Characteristics for GCSE Physics. Revise I-V Characteristics in Extra Topics for GCSE Physics with 13 exam-style questions and 11 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 12 of 12 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 12 of 12
Practice
13 questions
Recall
11 flashcards
Knowledge Organiser: I-V Characteristics
Key Terms
- I-V characteristic — graph of current vs voltage for a component
- Ohmic conductor — straight line through origin, constant R
- Threshold voltage — ~0.6 V for diode to start conducting
- Forward bias — direction diode conducts freely
- Reverse bias — direction diode blocks current
- Rectification — converting AC to DC using diode
Graph Shapes
- Resistor: straight line through origin
- Filament lamp: curve through origin, flattening at high V
- Diode (forward): flat then sharp upward curve at ~0.6 V
- Diode (reverse): flat (virtually no current)
Calculating Resistance
- R = V/I (from coordinates of a point)
- NOT from the gradient
- Gradient = I/V = 1/R
- Steeper line = lower resistance
Practical Setup
- Ammeter: in series with component
- Voltmeter: in parallel with component
- Variable resistor: adjusts current
- Reverse supply to get negative values
- Plot V on x-axis, I on y-axis
Key Equations
- V = I × R (Ohm's law — applies to ohmic conductors)
- R = V ÷ I (resistance from any point on an I-V graph)
- Ohmic conductor: straight line through origin on I-V graph
- Resistance = 1 ÷ gradient of I-V graph (for ohmic conductors)
Common Mistakes
- Plotting axes the wrong way: The convention for I-V graphs is voltage (V) on the x-axis and current (I) on the y-axis — reversing them makes the gradient meaningless
- Saying all components obey Ohm's law: Only ohmic conductors (e.g. resistors at constant temperature) obey Ohm's law — filament lamps, diodes, and thermistors are non-ohmic
- Reading resistance from an I-V graph incorrectly: Resistance at any point = V ÷ I (not the gradient) — for a straight line through the origin, resistance = 1 ÷ gradient, but for curved graphs use the point values
- Saying a filament lamp has constant resistance: As the filament heats up, its resistance increases — the I-V graph curves because resistance is not constant
- Forgetting diodes only conduct in one direction: A diode only allows current flow above a threshold voltage in the forward direction — in reverse bias, it has extremely high resistance and negligible current flows
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Practice Questions for I-V Characteristics
What does an I-V characteristic graph show for a component?
Explain why the I-V graph for a filament lamp is not a straight line.
Quick Recall Flashcards
13 questions on I-V Characteristics — practise free
Instant marking, adaptive difficulty, and 11 spaced repetition flashcards. Free until your GCSEs.
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