9702 · 9.1
Electric current — FAQ
Frequently asked questions for 9702 Electric current. Direct answers first, then deeper explanation — then practise with marking.
What is the main difference between charge and current?
Charge is a fundamental property of matter, like mass, existing as positive or negative. It's measured in Coulombs. Current is the rate at which this charge moves or flows past a point, measured in Amperes (Coulombs per second).
Why is the drift velocity of electrons in a conductor so slow, even with a high current?
Although the individual electrons have a high random speed, their net forward movement (drift velocity) is slow because they frequently collide with the lattice ions. However, there are so many free electrons (high number density, 'n') that even a slow net drift results in a substantial current.
How does an ammeter measure current, and how should it be connected?
An ammeter measures current by detecting the flow of charge through itself. To ensure it measures the total current flowing in a specific part of a circuit, it must always be connected in series with the component. Ideally, an ammeter has zero internal resistance to avoid affecting the circuit's current.