Page 197 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 3 Scientific principles

Electrons are arranged in varying distances from the nucleus – the further they
are away, the less they are attracted to the atom and are easily deflected from
their orbits to be attracted by other atoms. This constant to-ing and fro-ing
of electrons from one atom to another is the structure that makes electricity
possible. Materials that allow the movement of free electrons are known as
conductors and those that restrict their movement are known as insulators.

The measurement of electrical flow

Electricity is measured in two ways:
1 by the amount of current – this is the number of electrons flowing, measured
in amperes
2 by the voltage – this is the push, or pressure, which causes electrons to flow,
measured in volts.

The push or pressure that causes electrons to flow is also known as ‘potential
difference’. In a conductor the path is clear for electrons to move, and it is the
voltage (pressure) that makes them do so.

The units of electrical measurement

When we think about electricity we think in terms of voltage, amperage,
resistance and power, but what do these terms mean and what do they do?
Here, we will investigate the various electrical units, their interaction with one
another and how we can calculate one if two others are known (Ohm’s law).

Voltage
When a potential difference or voltage is applied across a circuit, electrons will
flow. The higher the potential difference or voltage, the greater the ‘pressure’ on
each electron. If the resistance in a circuit stays the same, then the larger the
potential difference the greater the current or flow (amps) in the circuit.

IMPROVE YOUR MATHS
Voltage can be calculated by:

Current (I) × Resistance (R)

Resistance
Resistance is the movement of electrons through a conductor. All electrical
circuits will have resistance but some will have more than others. Resistance in
some circuits is necessary to ensure that not too many electrons flow and, in
others, as little resistance as possible is required so that high current will flow.

There is a definite interaction between current (electron flow), voltage (current
flow) and resistance. As the electrical pressure (voltage) increases, more electrons
flow. Increasing the voltage also increases the amperes of current, but if resistance
is also increased this decreases the flowing current thus reducing the amperes.

185

9781510416482.indb 185 29/03/19 8:55 PM