Edexcel IGCSE Physics: Double Science 复习笔记：2.1.1 Charge & Current

• Electric current is defined as the rate of flow charge
  • In other words, the size of an electric current is the amount of charge passing through a component per second

   

• Current flows from the positive terminal to the negative terminal of a cell

Charge flows from the positive terminal to the negative terminal

• 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

In metal wires, the current is a flow of negatively charged electrons. This image shows the electrons flowing through a lattice of metal ions

• The charge, current and time are related by the equation:

• Where:
  • Q = charge measured in Coulombs (C)
  • I = current measure in amps (A)
  • t = time measured in seconds (s)

   

• This equation can be rearranged with the help of the following formula triangle:

ANSWER:  B

Step 1: Write out the equation relating current, charge and time

Q = It

• • This can be rearranged to make current I the subject of the equation:

   

Step 2: Rule out any obviously incorrect options

• • Option A does not mention time, so can be ruled out

   

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