Resistance and Resistivity

What Resistance and Resistivity covers

Resistance and Resistivity is examined in Unit AS 1, Forces, Energy and Electricity, and drawn on again in Unit AS 3, Practical Techniques and Data Analysis. It covers resistance and Ohm's law, ohmic and non-ohmic behaviour, resistors in series and in parallel, Investigating current, voltage and resistance in series and parallel circuits, electrical power and energy in resistive circuits, resistivity and the equation R = ρl/A, measuring the resistivity of a metal, current–voltage characteristics of a conductor, a lamp and a diode and resistance, temperature and superconductivity.

The 9 subtopics

Each one has its own page. CCEA AS Physics students sit this topic in the first year.

• Resistance and Ohm's lawResistance of a component, equation defining resistance and give the unit of each symbol and ohm's law.Open →
• Ohmic and non-ohmic behaviourDescribing a component as ohmic, describing a component as non-ohmic and shape of the current–voltage graph for an ohmic conductor.Open →
• Resistors in series and in parallelEquation for the total resistance of resistors connected in series, equation for the total resistance of resistors connected in parallel and why resistances simply add when resistors are connected in series.Open →
• Investigating current, voltage and resistance in series and parallel circuitsRecall questions on the apparatus and method for verifying the series and parallel rules, which quantity is common in each arrangement, where the ammeter and voltmeter go, why the current is kept small and the circuit switched off between readings, the junction rule, and the systematic error the meters themselves introduce.Open →
• Electrical power and energy in resistive circuitsRecall questions on P = VI and the derivations of P = I²R and P = V²/R, the factor of four when current doubles, calculating energy transferred over a time, why transmission is at high voltage, which of two resistors dissipates more in series and in parallel, and why a fuse melts.Open →
• Resistivity and the equation R = ρl/ARecall questions on the definition of resistivity and the equation with every symbol, the unit and how it follows, the dependence on length and on cross-sectional area, the effect of doubling the diameter, worked calculations on copper and nichrome wires, and why a wire stretched to twice its length quadruples its resistance.Open →
• Measuring the resistivity of a metalRecall questions on the apparatus and method, measuring the diameter with a micrometer and why it is taken in several places, finding the area from the diameter, what is plotted and what the gradient gives, why the current is kept small, which measurement dominates the uncertainty, and the effect of contact resistance.Open →
• Current–voltage characteristics of a conductor, a lamp and a diodeCurrent–voltage characteristic of a component, circuit used to obtain a current–voltage characteristic and current–voltage characteristic of a filament lamp.Open →
• Resistance, temperature and superconductivityRecall questions on how the resistance of a metal changes with temperature and why, the opposite behaviour of a negative temperature coefficient thermistor and its explanation, the shapes of both graphs, the experiment with a thermistor in a water bath, two uses of a thermistor, and superconductivity with its critical temperature.Open →

What you need to know

Answer each one before you reveal it.

Take Resistance and Resistivity further

The same content, four other ways.

Questions from this topic

Each one with the model answer underneath.

1. 1

   Define the resistance of a component.

   Model answer

   The resistance of a component is the potential difference across it divided by the current through it, R = V/I.

2. 2

   State the equation defining resistance and give the unit of each symbol.

   Model answer

   The equation is R = V/I, where R is the resistance in ohms, V the potential difference in volts and I the current in amperes.

3. 3

   Define the ohm.

   Model answer

   One ohm is the resistance of a component in which a potential difference of one volt drives a current of one ampere, so 1 Ω = 1 V A⁻¹.

4. 4

   State Ohm's law.

   Model answer

   The current through a conductor is directly proportional to the potential difference across it, provided the temperature and other physical conditions remain constant.

5. 5

   Why does the statement of Ohm's law include the condition that the temperature stays constant?

   Model answer

   The resistance of most conductors changes with temperature, so if a large current warms the conductor the ratio of potential difference to current alters and the proportionality is destroyed.

6. 6

   A potential difference of 12 V drives a current of 0.40 A through a resistor. Calculate its resistance.

   Model answer

   The resistance is R = V/I = 12 ÷ 0.40 = 30 Ω, and 0.40 A × 30 Ω returns the 12 V as a check.

What is inside Levo

Six ways to work the same material.

Resistance and Resistivity revision questions

Is Resistance and Resistivity examined at AS in CCEA Physics?

Yes. It sits in Unit AS 1, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.

What does Resistance and Resistivity cover in CCEA AS-Level Physics?

9 subtopics: resistance and ohm's law, ohmic and non-ohmic behaviour, resistors in series and in parallel, investigating current, voltage and resistance in series and parallel circuits, electrical power and energy in resistive circuits, resistivity and the equation r = ρl/a, measuring the resistivity of a metal, current–voltage characteristics of a conductor, a lamp and a diode and resistance, temperature and superconductivity. Each one has its own page with questions and model answers.

How is Resistance and Resistivity organised?

By the CCEA 1210 specification, subtopic by subtopic, so it matches the order you are taught it in.