llustration of the structure of dry cell batteries

On the outer shell of some dry cells, the two ends are marked with + and – symbols, and the words “voltage 1.5V” are written in the middle, indicating its electrodes and voltage.

The outer shell of a dry cell is a cylinder made of zinc, which contains chemicals. A carbon rod stands in the center of the zinc cylinder, and a copper cap is fixed on the top of the carbon rod.

Due to chemical changes in the dry cell, many positive charges gather on the carbon rod, and many negative charges gather on the surface of the zinc cylinder. The carbon rod and the zinc cylinder are called the electrodes of the dry cell. The carbon rod that gathers positive charges is called the positive electrode, and the zinc cylinder that gathers negative charges is called the negative electrode. The symbols + and – on the outer shell of the dry cell represent the positive and negative electrodes of the battery respectively.

“Voltage 1.5V” means that the voltage between the two poles of the battery is 1.5 volts. What is voltage? It can be explained by analogy with the situation of water flow.

If the switch is turned on, a water flow will be formed in the water pipe from the water tower to the user. This is because the water surface of the water tower is higher than the user, which generates water pressure in the water pipe connecting the two. The function of a water pump is to continuously pump water from a low place to a high place in a water tower, so that the water level at the water tower is always higher than that at the user’s place, and to maintain a certain water pressure between the two, so that the water can flow continuously.

When a small light bulb is connected between the two poles of a battery with a wire, the small light bulb lights up, indicating that there is current in the circuit. The free charges in the circuit can move in a directional manner to form a current because the positive pole of the power supply has excess positive charges and the negative pole of the power supply has excess negative charges, thus generating a voltage in the circuit. The function of a power supply is similar to that of a water pump. It continuously gathers positive charges on the positive pole and negative charges on the negative pole, maintaining a certain voltage between the two poles, so that current continuously flows through the connecting conductor.

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