Page 52 - Innovator's Science-8

Electric liquid is usually a weak acid or a salt solution and is kept in a
lamp Connecting
wire glass or plastic container. The metal plates, known as
electrodes, react with the electrolyte to create electric
Electric
current current. When connected in a circuit, electricity flows from
Glass
container the positive terminal through the circuit to the negative
terminal. After some time, the chemicals inside get used
Electrode 2
up, and the cell can no longer produce electricity. At this
Electrode 1 Electrolyte
(liquid) stage, it is called a “dead” cell.
The names Voltaic and Galvanic cells come from two Italian
scientists, Alessandro Volta and Luigi Galvani. In the late
1700s, Galvani discovered that a dead frog's leg moved
Simple representation of a voltaic cell
when it was touched with two different metals, copper and
iron. At that time, people already knew that electricity could make muscles

move, so Galvani thought the electricity came from the frog's body. However,
Volta believed that the electricity was actually produced due to the contact
between the two metals. To test his idea, he replaced the frog's leg with
paper soaked in salt water and still observed an electric current. This
Alessandro Volta experiment proved that electricity was generated from the chemical reaction

between the metals and the liquid, leading Volta to invent the world's first
battery.

You can make voltaic cell yourself in home. Take five or six juicy lemons,
copper wires/ strips (1–2 mm thick) and iron nails. Also take one LED and
some connecting wires.
Luigi Galvani
Insert a copper wire and the iron nail into one lemon, keeping them slightly
apart as shown.

Repeat the above step for all the remaining lemons.

Join the copper wires and nails as shown.
Connect the LED between the copper wire of the first lemon and
the iron nail of the last lemon, using connecting wires. What do you

observe? Does the LED glow?
a.
If the LED does not glow, reverse the connections
LED
of its tensional. Does the LED glow now?
[Remember that we have learnt earlier that
current can pass through the LED only when the
Copper Iron
strip nail positive terminal (longer wire) of the LED is

Lemon connected to the positive terminal of the battery,
b.
a. Electric cell made using lemons; and negative terminal (shorter wire) of the LED is
b. Connections in lemon cell
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Science-8