Download Current / Voltage Graphs

Current / Voltage Graphs
These graphs allow you to predict how the
component will behave when the conditions are
changed. It is very important to know, since this will
affect the circuit in which it is placed. You need to
memorise graphs for the following…
• (Ohmic) Conductors
• A filament lamp
• A diode
• A thermistor
• A light dependent resistor (LDR)
An Ohmic Conductor
If they are kept at a constant temperature,
V/I will always give the same value. This
value is equal to the RESISTANCE of the
component, and is measured in Ohms (W).
I (A)
Reading values off
the graph, then using
R = V/I will give the
resistance. The same
value of R will be
obtained from any
point on the graph.
V (V)
A filament lamp
A filament lamp does not illustrate Ohm’s
law since its temperature is not constant.
As a result, the resistance is not constant.
I (A)
Reading values off the graph, then
using R = V/I will give different
values of resistance from different
points point on the graph.
As the current through the filament
increases, more heat is produced,
which makes the lattice ions
vibrate. This obstructs the
electrons as they flow, so the
V (V)
resistance increases.
A Diode
Diodes are not metallic.
They are made from
semi-conducting
materials.
They do not always obey
Ohm’s law.
Diodes allow current to
flow in one direction only.
They can then be used to
convert an alternating
current to a direct
current.
I
V
More graphs for electrical components
A light dependent resistor
A thermistor
R
R
T
Light Intensity
Thermistors and LDRs
• These components are made out of semiconducting materials, so they do not
behave like metals.
• When given energy (like heat or light) they
conduct better since more electrons
become free to move through the material.
• These components are used in circuits to
help us to monitor and control devices
automatically (like automatic night lights).