Syllabus Edition

First teaching 2014

Last exams 2024

|

Primary & Secondary Cells (DP IB Physics: SL)

Revision Note

Katie M

Author

Katie M

Last updated

Primary & Secondary Cells

Simple Cells

  • A simple cell is a source of electrical energy
  • The simplest design consists of two electrodes made from metals of different reactivity immersed in an electrolyte and connected to an external voltmeter by wire, creating a complete circuit
  • A common example is zinc and copper
  • Zinc is the more reactive metal and forms ions more easily, readily releasing electrons
  • The electrons give the more reactive electrode a negative charge and sets up a charge difference between the electrodes
  • The electrons then flow around the circuit to the copper electrode which is now the more positive electrode
  • The difference in the ability of the electrodes to release electrons causes a voltage to be produced
  • The greater the difference in the metals reactivity then the greater the voltage produced
  • The electrolyte used also affects the voltage as different ions react with the electrodes in different ways

How Reactivity Affects Voltage in Cells 1, downloadable IGCSE & GCSE Chemistry revision notes

 

How Reactivity Affects Voltage in Cells 2, downloadable IGCSE & GCSE Chemistry revision notes

Simple cell made with Cu and Mg. These metals are further apart on the reactivity series than Cu and Zn and produce a greater voltage

Batteries

  • Electrochemical cells include the familiar batteries used in everyday appliances and cars
  • Batteries work by connecting two or more cells in series, which combine to give a larger overall voltage
  • Over time the electrodes degrade as the reactions that occur there are irreversible
  • Cells produce a voltage only until one of the reactants is used up and when this occurs the battery dies or goes flat
  • The products formed cannot be reverted back into reactants as the reaction is irreversible and the battery must be replaced
  • This happens in non-rechargeable batteries such as alkaline batteries
  • In rechargeable batteries the reactions are reversed by connecting the cells to an external electrical supply
  • This reverses the chemical reactions taking place allowing the cycle to be repeated

Primary Cells

  • Cells that are non-rechargeable are known as primary cells
    • Primary cells include AA batteries (known as dry-cells) common in many small devices

  • Primary cells are by definition only able to be used once as the chemicals within them are used up
  • During normal operation of a primary cell, the electrons flow from the negative plate to the positive terminal of the cell

Secondary Cells

  • Cells that are rechargeable are known as secondary cells
    • Secondary cells include:
      • Lithium-ion batteries used in laptops and other larger modern devices
      • Lead-acid batteries such as those used in cars and other motor vehicles

  • Secondary cells can be used many times as they are attached to a charger and the chemical reaction is reversed allowing the cells to store energy for use once again
  • When recharging a secondary cell, the electrons are forced from the positive plate to the negative terminal by an external current

You've read 0 of your 5 free revision notes this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.