### Theory:

Battery:
We can call cells ‘batteries’ only when two or more cells are combined. A cell is a single unit that converts chemical energy into electrical energy, but a battery is a collection of cells.
Combination of cells
• Batteries are a combination of one or more cells whose chemical reactions create a flow of electrons in a circuit.
• All batteries are made up of three fundamental components: an anode (positive), a cathode (negative), and some electrolytes.
• The electrolyte is a material that chemically reacts with the anode and the cathode.
In the above figure, cells are connected in series; thus, they will act as a battery.
The invention of a battery:
• In $$1780$$, Italian biologist and philosopher Luigi Galvani was dissecting a frog attached to a brass hook. When he touched the frog's leg with an iron scalpel, the leg jerked.
• Galvani assumed that the energy came from the portion of the leg itself, but his fellow scientist, Alessandro Volta, perceived it in another way.
• Volta formulated a theory that the frog's leg impulses were due to metals' reactions with different solutions.
• He repeated the experiment using a cloth soaked in salt solution instead of a frog's corpse, which resulted in a similar voltage.
• Volta published his findings in $$1791$$, and he developed the first battery named the voltaic pile in $$1800$$.
• It all started with a surprising accident involving the dissection of a frog. Alessandro Volta's invention is the root cause of nowadays modern battery.
Electric switch:
• To avoid the unnecessary usage of current in the electric circuit, we use the electric switch to control electric current.
• A device which is used to break or close an electric circuit is called an electric switch. When switch is in 'OFF' position, then the circuit is open therefore no current flows through the circuit and when the switch is in 'ON' position, then the circuit is complete thus current flows through the circuit.
• We are using different kinds of switches to turn our household electric devices on or off. Switches help us to start or stop the devices safely and easily.
Toggle switch

Slide switch

Rocker switch