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A DIGITAL THERMOMETER

PLAN

AIM

While keeping the voltage constant using a variable resistor. Vary temperature and take readings of

the temperature and the current, from this a graph can be made which you can find e, the charge on

the electron.

APPARATUS

Voltmeter

Milliammeter

Mercury thermometer

1 k variable resistor

Battery supplyDiode

Bunsen burner

Wires

Tripod

Gauze

Water

Circuit diagram and layout diagram for beaker & burner, thermometer & diode

METHOD

Heat will be applied to the water, reading will be taken of I and T when it increases by 50C

while stirring the water.

While varying the variable resistor to keep the voltage to 0.6 V record the current (I) byusing an ammeter set to mA as the readings will be low. Readings will not need to be

repeated as the ammeter is very accurate.

The second measurement will be to measure the temperature (T) of the diode using a

thermometer. This will give me an accuracy to 10C, they will be taken every 5

0C along with

I.

OTHER QUANTITIES

The main quantity to keep this a fair test will be to keep the voltage constant at all times

depending on what voltage you start on (eg 0.6 V) you will need to take a control which willbe the room temperature. Note the same apparatus should be used at all times.

REPEATS

As there is not any high uncertainties to be taken into account the reading should be

repeated only once. If there is a great margin then they could be repeated again.

SAFETY

There is no great danger that can come from this experiment but behaviour should be good

when taking the test.

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DATA

I = I0 exp ( -eV/kT) multiply this by ln

END OF PLAN

IMPLEMENTATION & READINGS

READINGS

At room temperature 230C V= 0.67 V, I = 6.36 mA

Containing ice T = 10C, I = 2.37 mA when V= 0.67 V

T/ C I/mA ln (I/mA)

0 2.37 0.863

15 4.09 1.409

20 5.46 1.697

25 6.20 1.825

30 7.74 2.046

35 9.43 2.244

40 10.84 2.383

45 12.70 2.542

50 14.92 2.703

55 18.07 2.894

60 22.0 3.091

65 24.4 3.195

70 30.1 3.405

75 35.0 3.555

80 39.1 3.666

85 48.0 3.871

90 56.6 4.036

95 61.8 4.124

100 71.2 4.265

I made sure the beaker was stable and used a retort stand to keep the wires from melting. I

used ice to get down to a low temperature. For every reading I removed the Bunsen at the

time of reading to improve accuracy.

I plotted a graph of my readings (see attached hand drawn graph)

ANALYSIS

GRAPH see attached

The graph shows that temperature is proportional to ln I, so as Tincreases so does ln I at the

same rate. Therefore the best line of fit is a straight one.

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GRADIENT & RESULTS

I also used the equation

m = eV/2k to find a value for e.

From the graph for the gradient calculation (4.32 1.13)/ 100 = 0.0319 0C-1

It turns out that e = 5.56 x 10-21

C, which is a lot smaller than the actual value of 1.6 x 10-19

C.

This must be down to m as all the others are constant.

UNCERTAINTIES

In this test the main error was reading the thermometer which gave an error of 10C . I

notices that at the coldest the temperature still read 10C despite the ice I took this as a

sign of the uncertainty and called it 00C.

The reading for I was uncertain but I had no idea by how much and the scale division is sosmall, 0.01 mA, that this is too small to make a difference.

I think my reading for T is pretty accurate since I removed the Bunsen when taking readings

so the temperature stopped rising. I also changed R at this time to keep V constant at the

new temperature.

There was probably some contact resistance in the plugs but this had very little effect I

expect.

MODFICATION FOR FUTURE

The main uncertainty was in the temperature so I would use a datalogger. This could be

used to give a constant reading of T and make it more accurate. It is also more precise than

the other thermometer.

CONCLUSION

From my results it clearly shows that a diode can show a rise or drop in temperature in its

surroundings. However e was a lot smaller.

From the equation V = IxR the voltage is a constant and the resistance you are decreasing as

temperature increases, therefore the current must increase to keep the voltage the same

because more current is needed to keep the same voltage as the diode increases in

temperature.

This shows that for the range 00C to 100

0C in space this specific diode can be used to show

the temperature of a space probe while adding little weight to the probe.

FURTHER WORK

Try different types of diode or increase the range of temperature to see if a slope occurs or

try having a smaller or larger voltage.

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