What causes the current to move through a battery?

The current flows through a battery due to a chemical reaction that occurs inside it. Batteries contain two electrodes, namely a positive electrode (known as the cathode) and a negative electrode (known as the anode), immersed in an electrolyte solution.

The chemical reaction takes place between the electrolyte solution and the electrodes. At the anode, a chemical reaction occurs that causes the release of electrons. These electrons, being negatively charged, are attracted towards the positive electrode or cathode.

To understand this process, let's take an example of a common alkaline battery. In an alkaline battery, the anode is made of zinc and the cathode is made of manganese dioxide. The electrolyte solution is usually a potassium hydroxide (KOH) solution.

At the anode:
Zn(s) → Zn²⁺(aq) + 2e⁻

The zinc metal loses electrons and forms positively charged zinc ions (Zn²⁺). These electrons released from the anode move towards the cathode.

At the cathode:
2MnO₂(s) + H₂O + 2e⁻ → Mn₂O₃(s) + 2OH⁻(aq)

In the cathode, the manganese dioxide (MnO₂) reacts with water (H₂O) and electrons (e⁻) to form manganese oxide (Mn₂O₃) and hydroxide ions (OH⁻). These hydroxide ions combine with the positively charged zinc ions from the anode to form zinc hydroxide (Zn(OH)₂).

The chemical reactions at both electrodes create an imbalance of charges, with excess electrons at the cathode and a deficit of electrons at the anode. This imbalance causes the electrons to flow through an external circuit, such as a wire, from the anode to the cathode, creating an electric current.

It is important to note that a battery also has a separator that prevents direct contact between the anode and cathode but allows the flow of charged species (ions) between them. This separator helps maintain the chemical reactions and prevents a short circuit.

By understanding the chemical reactions and the movement of electrons within a battery, we can explain how the current flows through it.