PAG 04.3 Using Non-Ohmic Devices As Sensors

Question 1

How does the resistance of a NTC thermistor vary with temperature?

Answer 1

As temperature increases, the resistance of the NTC thermistor will decrease

Question 2

Why should you avoid heating the water too quickly?

Answer 2

The thermistor and thermometer will have thermal intertidal. If you try to heat the water too quickly, the temperature of the thermistor thermometer won’t be the same as that of the water

Question 3

What is the advantage of heating the water very slowly when carrying out this experiment?

Answer 3

By heating the water very slowly, you are allowing the thermistor and thermometer to become as close in temperature to the water as possible

Question 4

What after precautions should be taken when using a Bunsen burner?

Answer 4

-hair and loose clothing should be tied back
-a heatproof mat should be used to protect the work bench
-the safety flame should be used when not directly heating the water
-avoid touching metal regions near flame

Question 5

What is the added risk when using wires near a bunker burner?

Answer 5

You must ensure that the wires don’t get caught on the Bunsen burner or touch any hot components

Question 6

What does a potential divider do?

Answer 6

A potential divider is an arrangement that allows a desired output voltage to be produced by producing the required ratio of resistances

Question 7

How could you cool the thermistor down to zero degrees in this experiment?

Answer 7

The experiment can start with the thermistor placed in a beaker of ice. This can then be heated sousing a Bunsen burner to produce resistance measurements from 0 right up to 100

Question 8

What should you do when you add hot water to ensure the temperature is constant throughout?

Answer 8

You should use a stirrer to stir the water before taking temperature readings

Question 9

How should you take a reading from a thermometer?

Answer 9

Thermometer readings should be taken at eye level to reduce parallax errors

Question 10

What graph could be plotted to obtain a calibration curve for temperature?

Answer 10

A graph of the output potential difference against temperature could be plotted. A curve of best fit can then be drawn in and this can be used as a calibration curve

Question 11

How does the resistance of an LDR vary with light intensity?

Answer 11

The resistance of an LDR increases as the light intensity decreases

Question 12

How can light intensity be measured?

Answer 12

Light intensity can be measured using a digital light sensor

Question 13

Suggest a method for varying the light intensity incident on the LDR

Answer 13

A lamp connected to a dimmer switch can be shone at the LDR. If this is done in a darkened laboratory you should be able to achieve a good range of light intensities

Question 14

How should the light sensor be positioned in this experiment?

Answer 14

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

Question 15

What graph could be plotted obtain a calibration curve for light intensity?

Answer 15

A graph of the output potential difference against light intensity could be plotted. A curve of best fit can then be drawn in and this can be used as a calibration curve

Question 16

How can your calibration curve be used to determine an unknown light intensity?

Answer 16

Move your LDR into a region of unknown light intensity and record the output potential difference. Draw a line across from this value on your graph to determine the corresponding light intensity

Question 17

When may it not be possible to accurately determine an unknown light intensity using your graph?

Answer 17

If the unknown light intensity is beyond the range of values you have plotted, extrapolation will have to be used. This may not be appropriate, especially if it is significantly outside the range of your data

Question 18

What safety precaution should be taken when working in a darkened laboratory?

Answer 18

Before starting the experiment, ensure that all trip hazards (such as bags and cables) are positioned out of the way

Question 19

Why is it important that the fixed resistor value isn’t too high?

Answer 19

If the fixed resistor is significantly larger than the thermistor resistance, changes in temperature resistance won’t result in a significant enough change in the output voltage. This will make it harder to measure how the output changes

Question 20

Why is it important that the fixed resistor value isn’t too low?

Answer 20

If the fixed resistor value is too low, it may result in the output voltage changing across too big a range of values. This range may exceed the range measurable using a voltmeter