Electricity – The Very Basics
Complete the following table
Physical Quantity / Symbol / Unit / Unit (abbr.)Ampere
C
Voltage
R
There are two types of electric charge:
Like charges , unlike charges
The electric charge is a conserved quantity, which means that it cannot be or . Other conserved quantities are
Atoms have electric charges inside them. The charge of a proton is +1.6 x 10-19 Coulombs. The charge of an electron is . This charge is called “elementary charge”.
A flow of charges is called a . The physical quantity tells you how many Coulombs flow per second. Thus, the formula connecting charge, current and time is
To make a current flow through a circuit, there must be a across it.
The voltage of a power source tells you how much energy each Coulomb of charge gets. Similarly, the voltage loss between two points in a circuit tells you how much energy each Coulomb loses when passing e.g. a bulb.
The most important components of an electrical circuit are:
!!! Make sure you still know the circuit symbols from last year!!!
Some circuit diagrams have arrowheads marked on them. These show the conventional current direction: the direction from to round the circuit. Electrons actually flow the other way, but this definition was made before the electrons were discovered.
Current passes easily through some materials, which are called, e.g. or . Materials, which do not let the current pass through it easily are called , e.g. .
Every load in a circuit has a specific resistance. If you have 2 circuits (each connected to the same power supply) with two loads having different resistance, the one with the higher resistance will give you a current. If you increase the voltage, the current
Ohm’s law gives you this relation-ship: