Download RESISTORS

RESISTORS
Always remember……
V = IR
(V= voltage in volts; I = current in amps; R = resistance
in ohms)
Special types of resistors
Diodes



A diode is a device
which allows current to
flow only in one
direction.
It is also known as a
rectifier
This is what a diode
looks like
Diodes



This is the circuit
symbol for a diode
Draw this symbol in
your books
The arrow on the
symbol shows the
direction the current
can flow.
Diode

If the diode is reversed it acts like a very high
value resistor and prevents current flow.
Diode

1.
2.
Uses of diodes
Protecting equipment
should the power be
connected the wrong
way round,
Converting a.c. into
d.c.
Light dependent resistor
The LDR
LDR

This is a resistor whose
resistance depends on
the amount of light
falling on it.
LDR



This is the circuit
symbol for a diode
Draw this symbol in
your books
The arrows
represent light
falling on the LDR
LDR
Resistance of an LDR



Light level
When light falls on an
LDR its resistance falls
rapidly.
In low light or the dark
– they act as high
resistors.
In bright light they
offer very little
resistance
LDR

LDR’s can be used to
switch on street lights
when light falls.
Thermistors
Temperature-dependent resistors
Thermistor

This is a resistor whose
resistance depends on
the temperature.
Thermistors


This is the circuit
symbol for a
thermistor
Draw this symbol in
your books
Thermisitors

Thermistors are used in
circuits which are
designed to be
controlled by
temperature, such as a
sprinkler system.
Investigating thermistors
Temp
oC
Calculate the resistance at 5 different
temperatures
Volts
Amps
Resistance
V
A
ohms

Plot a graph of resistance against temperature
for your thermistor.