PAG 4.3 - Using Non-ohmic Devices As Sensors Flashcards
How does the resistance of a NTC thermistor vary with temperature
As temp increases, resistance of NTC thermistor decreases
Why should you avoid heating the water too quickly?
Thermistor and thermometer will have thermal inertia. The reading will not be the same as the actual temp of the water
What is the advantage of heating the water very slowly when carrying out this experiment
By heating the water very slowly, you are allowing the thermistor and thermometer to become as close in temperature as possible
What safety precautions should be taken when using a Bunsen burner?
- hair and loose clothing should be tied back
- heatproof mat should be used to protect work bench
- safety flame when not directly heating the water
- avoid touching metal regions near the flame
What is the added risk of using wires near a Bunsen burner?
Must ensure that the wires do not get caught on the Bunsen burner or touch any hot components
What does a potential divider do?
Allows a desired output voltage to be produced, desired ratio of resistances
How could you cool a thermistor down to 0 degrees in this experiment?
Thermistor placed in beaker of ice, and heat using a Bunsen burner to get 0 degrees up until 100
What should you do when you add water to ensure the temperature is constant throughout?
Use a stirrer to stir the water before taking temp readings
How should you take readings from a thermometer
Eye level to reduce parallax error
What graph could be plotted to obtain a calibration curve for temperature
Output PD against temperature
How does the resistance of an LDR vary with light intensity?
Resistance of LDR increases as light intensity decreases
How can light intensity be measured?
Digital light sensor
Suggest a method for varying the light intensity incident on an LDR
Lamp connected to a dimmer switch can be shone at the LDR
Darker lab to achieve a good range for light intensities
How should the light sensor be positioned in this experiment?
Light sensor should be as close to the LDR as possible, without covering it
This is so that it is exposed to the same light intensity as the LDR itself
What graph could be plotted to obtain a calibration curve for light intensity?
Potential difference against light intensity
How can your calibration curve be used to determine an unknown light intensity?
Move your LDR into a region of known light intensity and record the output potential difference. Draw a line across from this value and determine corresponding light intensity
When may it not be possible to accurately determine an unknown light intensity?
Beyond the range of values you have, extrapolation may not be appropriate
What safety precautions should be taken in a dark Labratory?
Ensure all tripping hazards are out of the way
Why is it important the fixed resistor value isn’t too high?
If the fixed resistor is significantly larger than the thermistor resistance, changes in temperature will not result in a significant enough change in output voltage
Why is it important that the fixed resistor value is not too low?
It may result in the output voltage changing across too big a range of results, may exceed the range measurable using a voltmeter
