AS · Practice questions · Resistance and resistivity

Opposition to the flow.

Six original Cambridge-style questions on R = V/I, R = ρL/A, and I-V characteristics.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Component and material.

Resistance: R = V/I.
Material: R = ρL/A.
Ohmic: straight I-V line.

Analysis

[2 marks]

State Ohm law and the condition under which it applies.

The current is proportional to the potential difference ✓
provided the temperature (and other physical conditions) stays constant ✓

Analysis

[2 marks]

A potential difference of 9.0 V drives a current of 0.30 A through a resistor. Find its resistance.

R = V/I = 9.0/0.30 ✓
R = 30 Ω ✓

Analysis

[3 marks]

A wire of length 10 m and cross-sectional area 2.0 × 10⁻⁷ m² is made of material of resistivity 1.7 × 10⁻⁸ Ω m. Find its resistance.

R = ρL/A = (1.7 × 10⁻⁸ × 10) / (2.0 × 10⁻⁷) ✓
R = 0.85 Ω ✓

Analysis

[3 marks]

A 2.0 m wire of cross-sectional area 1.0 × 10⁻⁷ m² has a resistance of 4.0 Ω. Find the resistivity of the material.

ρ = RA/L = (4.0 × 1.0 × 10⁻⁷) / 2.0 ✓
ρ = 2.0 × 10⁻⁷ Ω m ✓

Analysis

[2 marks]

Describe and explain the shape of the I-V characteristic of a filament lamp.

It is an S-shaped curve that bends away from a straight line as the voltage rises ✓
because the filament heats up and its resistance increases, so the current rises less steeply ✓

Analysis

[2 marks]

State how the resistance of a light-dependent resistor (LDR) changes as the light intensity increases, and how a thermistor (NTC) changes as it warms.

The LDR resistance decreases as the light gets brighter ✓
The NTC thermistor resistance decreases as the temperature rises ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.