Curriculum
Course: Science — Third Preparatory
Login

Curriculum

Science — Third Preparatory

Science — Third Preparatory

0/8

Science — Third Preparatory 2026/2027

0/4

Unit 1 - Force, Motion, Acceleration and Physical Quantities

0/1
Text lesson

Unit 2 — Electricity and Magnetism

Science — Third Preparatory

Unit 2 — Electricity and Magnetism

1.2 Electric current intensity

1.2 Electric current intensity

  • Imagine watching cars cross a line on a race track.
  • In one lap 10 cars cross the line in one minute; in another lap 5 cars cross in one minute.
  • The first lap has a higher "rate of crossing".
  • The flow of charges in a wire is similar.
  • Electric current intensity (I) is the quantity of electric charge that passes through a cross-section of a conductor in one second.

I = Q / t

  • where Q is the charge in coulombs (C) and t is the time in seconds (s). The unit of current is the ampere (A), and 1 A = 1 C/s.
  • An ammeter measures current. It is connected in series with the part of the circuit whose current is to be measured.
  • A charge of 90 C passes through a lamp filament in 3 minutes. Find the current.
  • t = 3 × 60 = 180 s. I = Q/t = 90 / 180 = 0.5 A.

Worked example 2

  • How much charge flows through a wire carrying 2.5 A for 20 s?
  • From I = Q/t, Q = I × t = 2.5 × 20 = 50 C.
  • Meaning of a statement. "The current in a wire is 2 amperes" means that a charge of 2 coulombs passes through any cross-section of the wire each second.
Unit 2 — Electricity and Magnetism · 3 / 20