Download how_hot_is_it

How hot is it?
• Current – Voltage graphs
• Dependence of resistance on heat
• LDRs and thermistors
Current – Voltage graphs
What is the component represented by this
graph? A resistor at constant temperature
I
The gradient of the line is
Draw
another line
I/V, but
Lower
resistance
for a resistor with
R = V/I
lower resistance
higher
resistance
 gradient = 1/R
Higher resistance
V
The current through a resistor (at constant
temperature) is directly proportional to the
voltage. The steeper the gradient, the lower the
resistance
Filament lamp
Is the filament lamp an Ohmic conductor?
No, because the I – V graph is not a straight
line, i.e. I is not directly proportional to V.
The resistance of
I
the metal filament
Hot
inside the bulb
increases as the
Cool
filament gets hotter
V
Hot
As more
current
flows,
the metal
Write
on your
graph
“hot” and
filament“cool”
gets in
hotter,
so its resistance
the regions
where
increases.
That’s why
the graph
the filament
is hotter
and gets
flatter. cooler and explain why.
Diode
Is the diode an Ohmic conductor?
No, because the I – V graph is not a straight
line, i.e. I is not directly proportional to V.
I
There is current flowing
only when the voltage is
positive. This means
that almost no current
flows if the voltage is
applied in the reverse
0.6 V
V direction.
0.6 V isPoint
the voltage
ataxis
which
on the V
thethe
diode starts
working,
i.e.the
current
voltage
at which
current
flows through
it. This voltage is
starts increasing.
called Activation Voltage.
Light Dependent Resistor LDR
The resistance in LDRs depends on how much
light shines on them.
Resistance (Ω)
When is the resistance higher?
When it is darker!
When is the resistance lower?
When it is brighter!
Write on the light intensity axis
bright and dark in the appropriate
places.
Dark
Bright
Light intensity
Light Dependent Resistor LDR
The resistance in LDRs depends on how much
light shines on them.
Resistance (Ω)
Choose the right ending. As the light
increases…
1. the current decreases.
2. the current stays the same.
3. the current increases.
Dark
Bright
Light intensity
Thermistor
(Temperature Dependent Resistor)
The resistance in thermistors depends on the
temperature.
In what conditions is the
resistance higher?
In cool conditions!
In what conditions is the
resistance lower?
In hot conditions!
Resistance (Ω)
Write on the temperature axis hot
and cool in the appropriate places.
Cool
Hot
Temperature
Thermistor
(Temperature Dependent Resistor)
The resistance in thermistors depends on the
temperature.
Resistance (Ω)
Choose the right ending. As it gets
cooler…
1. the current decreases.
2. the current stays the same.
3. the current increases.
Cool
Hot
Temperature
Cell or Battery
Thermistor
Resistor
Diode
Filament lamp
LDR
Cell or Battery
Thermistor
Resistor
Diode
Filament lamp
LDR