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# The aim of my Hot Water Tap Thermometer is to create an electronic thermometer that will accurately measure the Hot Water Tap's water temperature.

Extracts from this document...

Introduction

Hot Water Tap Thermometer

Context

It can be dangerous when placing your hand under a hot water tap, as you can never tell if the water is going to be too hot or not. The water can cause some scalding to the skin. I have researched and found that the average hot water temp is 50 oc. And that the skin can be scaled above 60 oc.

Aim

The aim of my Hot Water Tap Thermometer is to create an electronic thermometer that will accurately measure the Hot Water Tap’s water temperature. I am going to use an electronic circuit to measure the temperature and use the voltage to calculate the temperature.

Theory of Semi-Conductors

At ordinary temperatures, they only have a few free electrons. As the temperature increases more electrons are liberated

In insulators the energy gap between the two bands is large, so they have few electrons in the conductor band (this means no conduction can happen.) in semi-conductors energy bands close to the conduction bands are created. When heated enough energy is given to electrons to move the conduction band and the current increases.

Middle

60

0.65

0.62

0.66

70

0.53

0.51

0.57

Supply voltage = 3.03 volts

Resistance = 500 ohm’s

##### Things to change
• I will use the higher supply voltage of 5 volts to make my data more accurate
• I will increase the resistance of the resistor in series with the thermister to 10’000 ohm’s (10 K ohm’s) this should increase the resolution of my results.
• I will make sure that the thermistor is placed at the top of the beaker containing the water so that the highest temp of the water is recorded.
• I will repeat each temperature 5 times so that I will have a clearer average and any strange results can be noticed.
• I will measure between 30 and 65 oc and will increase the temperature in multiples of 5, i.e. 30,35,40,45…etc

Circuit Diagram

Safety

I will follow the following safety point so that I do not injure others or myself.

• I will make sure that my circuit is safe before I connect the power to it.
• I will be careful when using the hot water, so that I do not scald my skin
• I will keep the voltage of the power pack low so that I can not be electrocuted
• Make sure that the water I am using does not connect with the electrics

Fair test

It will be very important during my experiment that I keep the conditions of the experiment the same so that my results are correct.

Below is a list of points that helped my test to be fair:

• I used the same voltage throughout the experiment
• I made sure that the thermistor was at the same depth in the water for each reading.
• I made sure that the resistance of the resistor in the series circuit remained the same.
• I will use the same power amount of water for each reading

Conclusion

## The average Change (Sensitivity) is = 0.023371 per degree

Resolution

Resolution is the smallest change that the circuit can detect. This determines how accurate the reading is.

## 50oC = 0.60 v       52 oC = 0.56

Response time

Response time is the time it takes for my circuit to respond to the change in temperature then give the output. I had a lot of difficulty calculating the response time of my circuit. This was because the response time of my circuit was much quicker than any thermometer I had. So it was detecting the change almost instantly, where as the glass thermometer was taking up to a few seconds. This meant that I had nothing to compare my circuit’s readings to.

### Conclusion

Now that I have finished my experiment and collected and analysed my results I will now sum up what I have recorded. My results have shown that I predicted correctly and that the temperature is inversely proportional to the voltage across the thermistor.

This proves the theory that a thermistor is a semi-conductor, and that it behaves different from conductors. When the temperature of the thermistor increases, the current increases and the resistance drops.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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