What is one coulomb in terms of the ampere?

The charge transferred by a current of 1 A in 1 s.

State the relationship between charge, number of carriers and elementary charge.

Q = Ne, where e = 1.60 × 10⁻¹⁹ C.

Define potential difference.

The energy transferred per unit charge as charge moves between two points: V = W/Q.

What is a volt in terms of joules and coulombs?

One joule per coulomb, 1 V = 1 J C⁻¹.

The ratio of the p.d. across a component to the current through it: R = V/I.

The current through a metallic conductor is directly proportional to the p.d. across it, provided the temperature is constant.

Why is Ohm's law described as a special case of R = V/I?

R = V/I always defines resistance; Ohm's law applies only to conductors where V/I stays constant.

What does an ohmic conductor's I–V graph look like?

A straight line through the origin.

Why does a filament lamp not obey Ohm's law?

Current heats the filament, so ions vibrate more, collisions increase and the resistance rises.

Which direction does conventional current flow?

From the positive terminal to the negative terminal, opposite to electron flow.

Current, potential difference and resistanceEdexcel International A Level Physics: Flashcards

Card 1 of 120 of 12 known

Question

Define electric current and give its equation.

Tap or press Space to reveal

Tap card or press Space to flip

See all 12 cards

Define electric current and give its equation.: The rate of flow of charged particles: I = Q/t (or ΔQ/Δt).
What is one coulomb in terms of the ampere?: The charge transferred by a current of 1 A in 1 s.
State the relationship between charge, number of carriers and elementary charge.: Q = Ne, where e = 1.60 × 10⁻¹⁹ C.
Define potential difference.: The energy transferred per unit charge as charge moves between two points: V = W/Q.
What is a volt in terms of joules and coulombs?: One joule per coulomb, 1 V = 1 J C⁻¹.
Give the equation for energy transferred using V, I and t.: W = VQ = VIt.
Define resistance.: The ratio of the p.d. across a component to the current through it: R = V/I.
State Ohm's law.: The current through a metallic conductor is directly proportional to the p.d. across it, provided the temperature is constant.
Why is Ohm's law described as a special case of R = V/I?: R = V/I always defines resistance; Ohm's law applies only to conductors where V/I stays constant.
What does an ohmic conductor's I–V graph look like?: A straight line through the origin.
Why does a filament lamp not obey Ohm's law?: Current heats the filament, so ions vibrate more, collisions increase and the resistance rises.
Which direction does conventional current flow?: From the positive terminal to the negative terminal, opposite to electron flow.

Exam questions on Current, potential difference and resistance

A student connects a small electric motor to a 6.0 V battery of negligible internal resistance. The motor draws a steady current of 0.50 A for 3.0 minutes, and the whole 6.0 V is across the motor.
Calculate the number of electrons that pass through the motor in this time. (Elementary charge e = 1.60 × 10⁻¹⁹ C.)2 marks
A student investigates a length of nichrome wire kept at a constant temperature in a water bath. She measures the current for different potential differences across the wire and records: 0.10 A at 0.50 V, 0.20 A at 1.00 V, 0.30 A at 1.50 V and 0.40 A at 2.00 V.
Use the student's data to decide whether the wire obeys Ohm's law. Justify your answer.2 marks
During a thunderstorm a lightning flash lasts 2.0 ms. A total charge of 24 C is transferred between the cloud and the ground through a potential difference of 1.5 × 10⁸ V. A metal lightning conductor on a nearby building carries the discharge and has a resistance of 0.015 Ω.
Calculate the mean current during the flash and the energy transferred.3 marks

See the full worksheet

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).