Explain What DC Stands For And What It Means ?

DIRECT CURRENT

After reading this section you will be able to do the following:

• Explain what DC stands for and what it means.
• Define what a good source of DC would be.

Now that we have a fairly good understanding of basic electricity terms and concepts, let's take a closer look at some more details of the electrical current itself.

The battery we have been using for a current/voltage source generates direct current, which simply means the current flows in only one direction.

As long as electrons are flowing through the atoms of the circuit, work is being done. We can see that work is being done in this circuit because it lights the light bulb. The actual amount of electrons that are flowing is determined by the type and size of the battery as well as by the size and type of the light bulb. We could reverse the polarity of the battery by switching the contacts (wires), and the current would flow in the opposite direction and the bulb would still light.

Either way the battery is connected to the circuit, current can only flow in one direction. Direct current (DC) can also be generated by means other than batteries. Solar cells, fuel cells, and even some types of generators can provide DC current.

Review

1. DC, or direct current means the electrical current is flowing in only one direction in a circuit.
2. Batteries are a good source of direct current (DC).

ATOM MODELS

After reading this section you will be able to do the following:

• Describe the basic structure of an atom.
• Explain what holds an atom together.

What is an atom composed of?

An atom is the smallest particle of any element that still retains the characteristics of that element. However, atoms consist of even smaller particles. Atoms consist of a central, dense nucleus that is surrounded by one or more lightweight negatively charged particles called electrons. The nucleus is made up of positively charged particles called protons and neutrons which are neutral. An atom is held together by forces of attraction between the electrons and the protons. The neutrons help to hold the protons together. Protons and neutrons are believed to be made up of even smaller particles called quarks. We will limit our discussions to protons, neutrons and electrons.

Niels Bohr was a Danish scientist who introduced the model of an atom in 1913. Bohr's model consists of a central nucleus surrounded by tiny particles called electrons that are orbiting the nucleus in a cloud. These electrons are spinning so fast around the nucleus of the atom that they would be just a blur if we could see particles that small. In our pictures and exercises the electron appears to orbit in the same path around the nucleus much like the planets orbit the Sun. But, please be aware that electrons do not really orbit in the same path. The electrons actually change their orbit with each revolution.

Review

1. Atoms are composed of protons, neutrons, and electrons.
2. The forces of attraction between the electrons and the protons hold an atom together.