Electricity: The Basics of Electric Charge and Current

Electricity

The smallest part in which matter can be divided is the atom. Its construction is like this:

Nucleus: protons - mass and positive charge / neutrons - mass and negative charge

Orbits of electrons: they do not have mass but they have negative electric charge

Electric charge is a property of subatomic particles which influences the action of forces between items.

Charges of the same sign repel each other / Charges of different signs attract each other

1 coulomb = 6.25x10^18 electrons / The atoms of an object can lose electrons and become charged / The atoms of an object can gain electrons and become charged / Electric current is the flow of electrons through a conductor material

An Electric Device

1) An electric device has a resistance of 20 (ampere) and is subjected to a voltage of 200V. You are asked:

1. Intensity of current
2. Electric power
3. Energy consumed in 2.5 hours

a) 200 = 20 x (x) --> 200/20 = x = 10 ( V = R x I )

b) X = 200 x 10 = 2000 P = 2000W ( P = V x I )

c) 2000 = E/9000 --> E = 18000000J ( P = E/T )

Association of Resistances

In series, the equivalent resistance is the sum of the different resistors: Rt = R1 + R2 + R3 + R4

In parallel, the reciprocal of the equivalent resistance is the sum of the reciprocals of the individual resistors: 1/Rt = 1/R1 + 1/R2 + 1/R3 + 1/R4

The total voltage is the sum of the voltage drops across each resistor: Vt = VR1 + VR2 + VR3 + VR4

Types of Material

• Conductors: allow electrons to flow through them
• Insulators: do not allow the passage of electrons through them
• Semiconductors: work as conductors under certain substances (germanium, silicon)

Analogies between Electric and Hydraulic Circuits

If there is a difference in water level between two tanks (difference in gravitational potential), water will flow through the pipe and may rotate the turbine.

By pressure: some materials, when subjected to pressure, develop a voltage in their surfaces and vice versa

By heating two different materials, a voltage appears at the junction of the materials

By electromagnetic effect: when a copper coil rotates inside a magnetic field, a voltage is induced in the coil in both direction and magnitude.

Direct Current

Direct current is the type in which both the voltage and the polarity remain constant over time.