ELECTRICITY
The structure of an atom
Every living and non-living matter is comprised of
atoms.
The central nucleus contains the :
Proton (positive charge)
Neutron (neutral charge)
The particle revolving around the nucleus:
Electron (negative charge)
SI unit of charge is called the coulomb, and its symbol is C.
Insulators vs. Conductors
A conductor is a material in which electricity easily
flows. Metals are typically excellent conductors because
the valence (outer shell) electrons in metal atoms are
not confined to any one atom. Rather, they roam freely
about a metal object. Metal are excellent conductors of
electricity (and heat) for this reason.
Eg: Copper, silver etc
An insulator is a material in which electricity does not
flow easily. That is, the charges do not move easily.
Most nonmetallic material are good insulators. Valence
electrons are much more tightly bound to the atoms and
are not free to roam about.
Eg: Rubber, plastic, glass etc
CURRENT
Current is the flow of charged particles in a circuit.
The wires of the circuit are composed of atoms that
are held together tightly but around them are many
free electrons.
The metal filament in the lamp and the metal parts
of the switch also has free electrons.
When you open the switch, or turn it off, the lamp
goes off.
For an electric current to flow, there must be a
complete circuit, with no gaps.
The diagram consists of a bulb, a battery consisting
of two cells and wires connecting the components.
Circuit symbols
Measuring Current
Current is measured using an ammeter
Ammeters should always be connected in series with the
part of the circuit you wish to measure the current
through.
VOLTAGE
As charge flows around a circuit, energy is transferred to or from the charge
Voltage is the amount of push given to the electrons to flow in the circuit.
Voltage is measure in volts (V)
A voltmeter is used for measuring voltage.
Measuring Voltage
Voltage can be measured using a voltmeter.
RESISTANCE
Resistance is the opposition to current.
The unit of resistance is the ohm (Ω)
For a given potential difference:
The higher the resistance, the lower the current
RELATIONSHIP BETWEEN CURRENT & VOLTAGE
As the voltage across a component is increased, the current in the component also
increases.
ELECTRICAL ENERGY
As electricity passes around a circuit, energy is transferred from the power source to the
various components.
As charge passes through the power supply it is given energy
As it passes through each component it loses some energy (transferring that energy to
the component)
TYPES OF CIRCUITS
1. Series circuit
2. Parallel circuit
Series Circuits
A series circuit consists of a string of two or
more components, connected end to end.
Current in Series: In a series circuit the current is
the same at all points
Parallel Circuits
A parallel circuit consists of two or more components attached along separate
branches of the circuit.
The advantages of this kind of circuit are:
The components can be individually controlled,
using their own switches
If one component stops working the others will
continue to function
Current in parallel circuit: In a parallel circuit, the
current splits up - some of it going one way and the
rest going the other
This means that the current in each branch will be
smaller than the current from the power supply.
OHM'S LAW
The current flowing through a metal wire is proportional to the potential difference across it.
Voltage, current and resistance are related by the following equation:
Voltage= Current x Resistance
