TOPIC: Electrical quantities
SUB-TOPIC: Electric current
Date: Wednesday, 10h January, 2024
Objectives:
• Know that electric current is related to the flow of charge
• Describe the use of ammeters (analogue and digital) with different
ranges
• Describe electrical conduction in metals in terms of the movement of
free electrons
• Know the difference between direct current (d.c.) and alternating
current (a.c.)
Charge
The wires in an electric circuit are made of metal,
because metal is a good conductor of
electric current.. In the wires, the current is a flow
of negatively charged electrons
Keywords- Electrons, electric charge, conductors, electric current,
Referencehttps://www.savemyexams.co.uk/igcse/physics/edexcel/19/revisi
on-notes/2-electricity/2-1-current-potential-difference-resistance/2-1-1-charge--current/
Where:
•
•
•
Q = charge measured in Coulombs (C)
I = current measure in amps (A)
t = time measured in seconds (s)
Example
When will 8 mA of current pass through an
electrical circuit?
A When 1 J of energy is used by 1 C of charge
B When a charge of 4 C passes in 500 s
C When a charge of 8 C passes in 100 s
D When a charge of 1 C passes in 8 s
ANSWER: B
Current
Step 1: Write out the equation relating current,
In metal wires, the current is a flow of negatively charged charge and time
Electric current is defined as the rate of flow charge
electrons. This image shows the electrons flowing through a
• In other words, the size of an electric current is the
Q = It
lattice
of
metal
ions
amount of charge passing through a component per
• This can be rearranged to make
second
current I the subject of the equation:
Current flows from the positive terminal to the negative terminal Calculating Electric Charge
of a cell
The charge, current and time are related by the
Step 2: Rule out any obviously incorrect
equation:
options
• Option A does not mention
time, so can be ruled out
Charge flows from the positive terminal to the negative terminal
Step 3: Try the rest of the options by applying the equation to
determine the correct answer
• Consider option B:
I = 4 / 500 = 8 × 10–3 = 8 mA
• Consider option C:
I = 8 / 100 = 80 × 10–3 = 80 mA
• Consider option D:
I = 1 / 8 = 125 × 10–3 = 125 mA
• Therefore, the correct answer is B