Resistance, Ohm's law and resistivity
Practice Flashcards
Flip to reveal answersDefine resistance.
Track your progress — Sign up free to save your progress and get smart review reminders based on spaced repetition.
All 12 Flashcards — Resistance, Ohm's law and resistivity
Sign up free to track progress and get spaced-repetition review schedules.
Question
Define resistance.
Answer
How hard it is to push current through a component: $R = \dfrac{V}{I}$ (voltage across it ÷ current through it). Unit: the **ohm (Ω)**.
Question
State Ohm's law.
Answer
The voltage across a component equals the current through it times its resistance: $V = IR$. Given in the data booklet as R = V ÷ I.
Question
What is the unit of resistance?
Answer
The **ohm (Ω)**.
Question
How do you find resistance from an I–V graph?
Answer
**R = V ÷ I** at a point on the graph. For a straight line through the origin, R is the same at every point.
Question
What does an ohmic component's I–V graph look like?
Answer
A **straight line through the origin** — current is proportional to voltage, so R is constant.
Question
What does a non-ohmic component's I–V graph look like?
Answer
A **curve** — R = V ÷ I changes from point to point, so the resistance is not constant.
Question
Why is a filament lamp non-ohmic?
Answer
As the current increases the filament gets **hotter**, and a hotter metal wire has a **higher resistance**, so the I–V graph curves over.
Question
Formula for the resistance of a wire?
Answer
$R = \dfrac{\rho L}{A}$ — resistivity × length ÷ cross-sectional area. Given in the data booklet (as ρ = RA ÷ L).
Question
In R = ρL/A, what does ρ represent?
Answer
The **resistivity** of the material (unit Ω m) — a property of the material itself, independent of the wire's shape.
Question
Double a wire's length — what happens to R?
Answer
R **doubles** — resistance is proportional to length (R ∝ L).
Question
Make a wire thicker (double its area A) — what happens to R?
Answer
R **halves** — resistance is inversely proportional to area (R ∝ 1/A).
Question
A resistor reads 12 V across it and 4.0 A through it. Resistance?
Answer
R = V ÷ I = 12 ÷ 4.0 = 3.0 Ω.
Read the notes
Full study notes for Resistance, Ohm's law and resistivity
Topic 2.5 hub
Current and circuits
More from Topic 2.5
All flashcards in this topic
Physics exam skills
Paper structures & tips
Track your progress with spaced repetition
Sign up free — Aimnova tells you exactly which cards to review and when, so you remember everything before your IB exam.
Start Free