ELECTRICITY
A lesson for a secondary school student, though this lesson could be
adapted to suit a younger child e.g. by reducing the length and
complexity of the comprehension work.
Duration of the lesson: 30 minutes
Required Materials: Reference book on electricity, paper, and a
dictionary.
Rationale: While this lesson may appear to be quite bogged down in
history, I actually think that this is a good way to teach science to
those who are not necessarily interested in science as a subject. If you
present the histories of different scientific topics, it may be more
interesting than just studying the topics as they exist now. I think
this also makes the Jacari lesson different from the school lesson, as
the latter tend to focus directly on the topic.
Comprehension Activities:
The following passage is an excerpt from ‘Electricity’, an Eyewitness
reference book, published in association with the Science Museum.
During the 18th century many scientists experimented with electric
charge in their laboratories. As yet, there were no practical uses for
electricity; what interested scientists was the quest for knowledge.
They observed how electric charge could be seen as sparks, and how it
behaved differently with different substances. Since electricity was
invisible, instruments were needed to detect and measure it. Initially,
progress was haphazard. There was no way to make a sustained flow of
electric charge – that came later from the battery.
- Ask your student to read the passage out.
- Ask your student to underline any words which they don’t
understand, and look these up together in the dictionary.
- Ask your student the following questions:
1) What did scientists in the 18th century observe about electric
charge?
2) Why were instruments needed to detect electricity?
3) What was the main problem with experimentation – what did
scientists fail to do?
- Encourage your student to phrase their answers in their own words
(though it is also encouraged to look back at the text).
- You may want to mix up the order of the questions, so that your
student has to work a little harder to find the answers from the
text.
Researchers found that the simplest electricity-making unit, or electric
cell, was two plates of different metals in a jar filled with liquid.
The metal plates are called electrodes. They are conductors through
which electricity can enter or leave. The positive electrode is called
the anode and the negative electrode is called the cathode. The liquid,
which must be able to conduct electricity, is called the electrolyte.
Several cells joined together form a battery. There have been many types
and sizes of cells and batteries. Some of them used strong acids or
other noxious chemicals as the electrolyte.
- Again, begin by looking up unknown words in the dictionary e.g.
noxious.
- Go through the text with your student and together highlight any
words that appear to be very important e.g. ‘conductors’,
‘electrolyte’, ‘electrodes’ etc.
- Copy these words onto a set of flashcards (cut from your coloured
cards).
- Use the passage to create a definition that will be put onto the
back of the cards. Again, encourage these definitions to be from
the student’s own words.
Looking at different types of batteries:
After reading the following passages on different types of batteries,
ask your student to fill out the table below.
THE CAR BATTERY:
These rechargeable, lead-acid batteries are known as accumulators. Each
cell consists of two lead plates, or electrodes, separated by sulphuric
acid. As the battery in charged, lead oxide forms on one of the plates,
storing the incoming electrical energy in chemical form.
LECLANCHE CELL:
During the 1860s, French chemist Georges Lechlanche (183801882) devised
a cell in which one electrode was a zinc rod, and the other was a carbon
rod inside a pot of manganese dioxide and carbon granules. Between was a
solution of ammonium chloride. The cell produced about 1.5 volts. It did
not contain dangerous acid, and it soon became a popular and relatively
portable electricity-maker, and the forerunner of the torch battery.
DANIELL CELL:
English professor John Daniell (1790-1845) developed a simple cell in
1836 that provided current for a longer period. His cell (right) had a
copper cylinder as the positive electrode in copper sulphate, and a
zinc rod as the negative electrode in sulphuric acid, separated by a
porous pot. It produced about one volt and supplied electricity for
research.
Name of Cell Anode Material Cathode Electrolyte
Material
Daniell Cell
Car Battery
Leclanche Cell
N.B. From the passages it is sometimes difficult to determine the
electrolyte substance, so don’t worry too much if you can’t work it out
– just leave the box empty. The activity is more about learning the
terms ‘anode’, ‘cathode’ and ‘electrolyte’.
As a final exercise, go through the flashcards that you made earlier in
the lesson, presenting either the word or the definition to your student
and asking for either the definition or the word in response.