6. How Batteries Generate Electricity

Last updated at June 22, 2026 by

Cells, Batteries and Electrodes

  • An electric cell is a source of current
  • One cell gives 1.5 volts
  • Cells joined in series form a battery
  • An electrolyte conducts electricity
  • An electrode lets current enter or leave
Example 1 — Cells in a torch
  • each cell gives 1.5 volts
  • several joined in series
  • together they form a battery
Example 2 — Electrolyte and electrode
  • copper sulphate solution conducts
  • carbon or metal rods are electrodes
  • used inside a cell
Important Points
  • Cells are in series when the positive terminal of one joins the negative of the next.
  • Solutions of acids, bases and salts in water are electrolytes.
  • Electrodes are of two types — anode and cathode.
Definition — Battery
A battery means a group of cells joined in series.

Voltaic Cell

  • The first cell ever made
  • Changes chemical energy to electrical
  • Has a vessel with an electrolyte solution
  • Two electrodes are dipped in it
  • Copper is positive, zinc is negative
Example 1 — Copper-zinc cell
  • copper and zinc in dilute acid
  • copper acts as cathode
  • zinc acts as anode
Example 2 — Lemon cell
  • copper wire and iron nail in lemons
  • lemon juice is the electrolyte
  • an LED glows when connected
Important Points
  • It was named after Luigi Galvani and Alessandro Volta.
  • When the circuit is complete, current flows from cathode to anode (positive to negative electrode).
  • Lemon juice is a very weak electrolyte, so an LED is used instead of a bulb to detect the weak current.
Definition — Voltaic Cell
A voltaic cell means a cell, with two electrodes in an electrolyte, in which chemical energy is converted into electrical energy.
🔬 Activity 5 — Constructing a Voltaic Cell
Materials needed
5 fresh lemons, copper wire, iron nails, an LED bulb.
Procedure
Insert a copper wire and an iron nail into each lemon.
Connect one terminal of the LED to the copper wire of the first lemon and the other terminal to the iron nail of the last lemon.
Observation
The LED glows (reverse the connection if it does not glow at first).
Explanation
The copper wire and iron nail act as electrodes and the lemon juice as electrolyte, so the cell produces current that lights the LED.

→ Lemon juice can work as an electrolyte.

◆ Summary
  • Copper and iron are electrodes.
  • Lemon juice is the electrolyte.
  • The LED glows.

Dry Cell and Rechargeable Battery

  • A dry cell is a portable current source
  • It uses a moist paste, not liquid
  • Zinc container is the negative anode
  • Carbon rod is the positive cathode
  • A rechargeable battery can be reused
Example 1 — Zinc-carbon dry cell
  • zinc case is the anode
  • carbon rod is the cathode
  • used in clocks and torches
Example 2 — Phone battery
  • a rechargeable secondary cell
  • charged and reused many times
  • used in mobiles and laptops
Important Points
  • Ordinary dry cells are primary cells — they cannot be recharged.
  • Rechargeable batteries are secondary cells that can be charged and reused.
  • Lithium-ion batteries are widely used but are expensive and can pose fire or pollution risks.
Definition — Dry Cell
A dry cell means a portable electric cell that uses a moist paste instead of a liquid electrolyte.
🔬 Galvani, Volta and the First Battery
From frog's leg to voltaic pile. In 1780, Luigi Galvani saw a frog's leg muscle contract when touched by two different metals, calling it "animal electricity". Alessandro Volta later showed the frog was not needed — he used saltwater-soaked paper and metals to get a current, developing the first battery, the voltaic pile.
Q 1
Objective Type Questions Q1(f) - Page 69 Lakhmir Singh
Question

Name the following: The cell which uses a moist electrolyte.

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Dry cell

Explanation

  • A dry cell uses a moist paste instead of a liquid electrolyte.
Q 2
Objective Type Questions Q2(f) - Page 69 Lakhmir Singh
Question

Fill in the blank: The solution used in a voltaic cell is called ________. (NCERT Book Question)

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an electrolyte

Explanation

  • An electrolyte is a liquid that conducts electricity, such as dilute sulphuric acid.
Q 3
Objective Type Questions Q3(g) - Page 69 Lakhmir Singh
Question

State whether true or false: Dry cells are less portable compared to Voltaic cells. (NCERT Book Question)

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False

Explanation

  • A dry cell uses a moist paste, so it can be carried in any direction without spilling, making it more portable than a voltaic cell.
Q 4
Objective Type Questions Q4 - Page 69 Lakhmir Singh
Question

Match Column A with Column B: (a) Voltaic cell (b) Electric iron (c) Nichrome wire (d) Electromagnet — with (i) Best suited for electric heater (ii) Works on magnetic effect of electric current (iii) Works on heating effect of electric current (iv) Generates electricity by chemical reactions. (NCERT Book Question)

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(a)–(iv), (b)–(iii), (c)–(i), (d)–(ii)

Explanation

  • Voltaic cell → generates electricity by chemical reactions.
  • Electric iron → works on heating effect of current.
  • Nichrome wire → best suited for electric heater.
  • Electromagnet → works on magnetic effect of current.
Q 5
Subjective Type Questions - Short Answer Q8 - Page 70 Lakhmir Singh
Question

In the figure given, in which case the LED will glow when the switch is closed? (One set-up has lemon juice; the other has pure water.) (NCERT Book Question)

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The LED glows in the set-up with lemon juice, not the one with pure water.

Explanation

  • Lemon juice is an electrolyte, so it conducts the weak current that lights the LED.
  • Pure water does not conduct electricity well, so no current flows and the LED stays off.
Q 6
21st Century Skills Q4 - Page 73 Lakhmir Singh
Question

A student sets up a simple voltaic cell by placing a strip of zinc in a beaker of dilute sulphuric acid and connecting it with a wire and bulb to a strip of copper placed in another beaker of dilute sulphuric acid. The bulb was glowing. (a) Identify the cathode, anode and the electrolyte. (b) What will happen if sulphuric acid is replaced with vinegar solution?

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Copper is the cathode, zinc the anode, dilute sulphuric acid the electrolyte; vinegar still works but the bulb glows dimmer.

Explanation

  • (a) Copper is the cathode (positive electrode), zinc is the anode (negative electrode), and dilute sulphuric acid is the electrolyte.
  • (b) Vinegar is a weaker electrolyte than sulphuric acid, so the cell still works but produces a weaker current and the bulb glows more dimly.
Q 7
Multiple Choice Questions Q11 - Page 72 Lakhmir Singh
Question

Choose the correct statement(s): A. Dry cells can be used multiple times. B. In a voltaic cell current flows from cathode to anode. C. Rechargeable batteries are also called secondary cells. D. Dry cells use a liquid electrolyte.

  • (a) A and B
  • (b) B and C
  • (c) C and D
  • (d) A, C and D
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(b) B and C

Explanation

  • In a voltaic cell current flows from cathode to anode, and rechargeable batteries are secondary cells.
  • Dry cells cannot be reused and use a moist paste, not a liquid electrolyte, so A and D are wrong.
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