how hot is it? current – voltage graphs dependence of resistance on heat ldrs and thermistors
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How hot is it?
• Current – Voltage graphs
• Dependence of resistance on heat
• LDRs and thermistors
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Current – Voltage graphsWhat is the component represented by this
graph? A resistor at constant temperature
V
I Draw another line for a resistor with lower resistance
Lower resistance Draw another line
for a resistor with higher resistance
Higher resistance
The current through a resistor (at constant temperature) is directly proportional to the voltage. The steeper the gradient, the lower the resistance
The gradient of the line is I/V, but
R = V/I
gradient = 1/R
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Filament lampIs 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.
V
I The resistance of the metal filament inside the bulb increases as the filament gets hotter
Hot
Write on your graph “hot” and “cool” in the regions where the filament is hotter and cooler and explain why.
Hot
Cool
As more current flows, the metal filament gets hotter, so its resistance increases. That’s why the graph gets flatter.
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DiodeIs 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.
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 direction.
Point on the V axis the voltage at which the current starts increasing.
0.6 V is the voltage at which the diode starts working, i.e. current flows through it. This voltage is called Activation Voltage.
0.6 V
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Light Dependent Resistor LDRThe resistance in LDRs depends on how much light shines on them.
Light intensity
Resistance (Ω) When is the resistance higher?
Write on the light intensity axis bright and dark in the appropriate places.
When it is brighter!When is the resistance lower?
When it is darker!
Dark Bright
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Light Dependent Resistor LDRThe resistance in LDRs depends on how much light shines on them.
Light intensity
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
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Thermistor (Temperature Dependent Resistor)
The resistance in thermistors depends on the temperature.
Temperature
Resistance (Ω) In what conditions is the resistance higher?
Write on the temperature axis hot and cool in the appropriate places.
In cool conditions!
In hot conditions!
Cool Hot
In what conditions is the resistance lower?
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Thermistor (Temperature Dependent Resistor)
The resistance in thermistors depends on the temperature.
Temperature
Resistance (Ω)
Cool Hot
Choose the right ending. As it gets cooler…
1. the current decreases.
2. the current stays the same.
3. the current increases.
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Cell or Battery
Resistor
LDR
Diode
Thermistor
Filament lamp
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Cell or Battery
Resistor
LDR
Diode
Thermistor
Filament lamp