Perfecting the electric cell

Voltage/Potential difference

• The voltage between the two electrodes is dependent on the type of electrode used
• When magnesium and copper are used the potential difference between the two electrodes is fairly high
• Enough current flows to even light a bulb
• If copper and zinc are used the voltage is insufficient to light the lamp
• The current can however be read on an ammeter
• A voltmeter can also be used to measure the voltage of the cell
• It will show that the magnesium-zinc battery produces a higher voltage and more current than a copper-zinc cell

• The table above shows the metals which could be used to make an electric cell
• The least reactive metal can be used to make the positive terminal
• The most reactive metal will be used to make the negative terminal
• The further apart the minerals in the series the greater the potential difference (voltage)
• For example the Magnesium-Copper cell gives the most potential difference
• The Lead copper cell would give the least potential difference
• A simple with a zinc plate for an electrode and
• A copper plate for an electrode
• and dilute sulphuric acid as an electrolyte
• produces about 1 volt

Polarisation

• After only a short time the cell stops working due to polarisation
• Polarisation-this is when hydrogen bubbles collect on the copper plate of a simple electric cell and act as an insulator
• Polarisation can be overcome by wiping the bubble off the plate at intervals
• It can also be solved by adding a depolirising agent
• A little potassium manganate (VII) to oxidise the hydrogen as soon as it forms

To access more topics go to the Combined Science Notes page.