(Negative Thermal Co efficient)
Wire Iron Core for Electromagnet
Hammer x1 Bell x1
Metal Disc (magnetic) x1 Bunsen burner x1
Cup of Water with ice Heatproof mat
Risk Assessment
There are a lot of safety issues in this investigation. There is the risk of electrocution from the wires as at the end it is only live wire and if not use properly it may be fatal.
The power supply may also cause electrocution.
Also there may be electrocution from the cup of water as it will be used to cool down the thermistor as it is very sensitive but water conducts electricity so it will have to be handled with care.
I may get burnt by the Bunsen burner as it can get very hot and this can burn my skin.
As this is electricity I don’t know if the circuit may just blows, this is another factor.
As you see there are lots of safety issues to contemplate during the investigation.
Working On the Fire Alarm
- Firstly I started by making my circuit connecting the power supply with the thermistor leaving out the electromagnet.
- Then I made my electromagnet coiling around the iron core with wire. I then connected this onto the main circuit.
- I then got the hammer and put in the middle the metal disc making sure that it would definitely be attracted by the electromagnet.
- After this I put on the bell where it would be hit by the hammer.
- This completed the circuit. Now I checked again to male sure there were no breaks in the circuit as it would result in the circuit not functioning at all.
- Now I would test my fire alarm so I could analyse it. Its strength and weaknesses.
- I tested my switch by putting the NTC thermistor over a Bunsen burner. If successful the resistance would become low causing the circuit to be complete and I should observe the bell ringing. If not then there is a break somewhere in the circuit and I will have to check the circuit again.
- To stop the bell ringing the thermistor should be placed in a cup of cold water and it should then cool causing a high resistance and the circuit being incomplete again and the ringing brought to an end.
Conclusion
From the investigation I learnt that my fire alarm does work properly and that it could be used properly.
I learnt that the electromagnet worked perfectly and my idea of it causing a ringing by attraction did work.
I learnt that positioning is a vital part of this investigation as just being a bit off, can result in the bell not ringing at all.
I learnt how to set up a circuit and making sure that there are no breaks in it as if it did the circuit would not function at all.
I have learnt the function and how to use a thermistor.
I have learnt how to accurately use and make an electromagnet.
How to attach wire to other electrical components to make a full complete circuit.
I learnt in the investigation that the flow of negative electrons which went from negative to positive as negative has more electrons and tries to balance this out.
But this flow of electron meets resistance in the thermistor as it is cold therefore the thermistor does not work.
But if the temperature does exceed the resistance in the thermistor becomes low and the flow of electron continues again.
This cause an electronic magnetic field to begin around the iron core. The magnet will then attract the metal disc and the hammer at the bottom will strike the bell. The bell being metal is sonorous and will make a ringing sound. As the metal disc is attracted the circuit is broken so the flow of electrons will seize. This will stop the magnetic field of the electromagnet and the attraction between the magnet and metal disc will stop.
This will make the hammer return to its original position causing it to complete the circuit and the process occurring again.
Evaluation
From the investigation I have got good evidence to come to a strong conclusion (see above).
The strengths in the investigation are that the circuit run as I hoped for it to, showing me that the fire alarm does work.
My idea of the electromagnet did work and my prediction of how the circuit would work is correct.
Weaknesses in the investigation are that the thermistor being made of plastic melted when it was placed on the Bunsen burner. I will show how to improve this below.
I found that I had to make the position of everything had to be precise or the circuit would not work at all as there would be no flow of electrons due to breaks in the circuit.
Improvements
I stated above that the Bunsen burner melted the thermistor so I would cover this up with a shell which would not damage the thermistor but another question arises? Will the shell affect the temperature?
The thermistor is very sensitive. It started going of at room temperature but this is because its resistance is only 100 Ω (ohms) and so its temperature at which resistance will become low is about room temperature so I will use a thermistor which is at 10 000 Ω (ohms) which will only react to high temperatures around that of fires.
