# How to measure temperature of a wire without connecting it to a ckt

1. Jun 18, 2013

### physicsEEprob

Hi, I'm doing a physics extended essay and my independent variable is the temperature of a copper wire. I need to be able to alter this temperature without connecting it to a circuit and was wondering if anyone had any suggestions on whether there is a special type of equipment (such as a probe) or methodology that would help me to do this. Is there any way I could accurately/precisely measure the temperature after immersing it in water of a specific temperature? Sorry if this is not the right place to post this-just joined!

2. Jun 18, 2013

### Staff: Mentor

Do you want to alter or measure the temperature?
If it is immersed in water: Do you expect significant deviations from the water temperature?
Can you glue a temperature sensor on it?
Without water, an infrared thermometer/camera could work.

3. Jun 18, 2013

### physicsEEprob

I would like to alter the temperature in a why that will produce a constant heat across the wire--I would like to have five measurements of different temperatures in the end. However after altering the temperature I need to accurately measure the temperature of the wire to make sure that it is at its designated fixed temp. So I suppose both to answer your first question.
Yes I expect it to deviate from the water temperature which is why I need an accurate way of measuring it as well as altering it.
I'm not sure what you mean when you suggest glueing a temperature sensor--could you explain it a bit? (sorry I'm not exactly an advanced physics student)
And yes, I thought about an infrared thermometer but would that give me a temperature reading for the whole wire or just the small point it reads?

4. Jun 18, 2013

### Staff: Mentor

Resistance thermometer

Alternatively: if you know the thermal conductivity of the wire and its power, it should be possible to calculate its temperature difference to the water around it. If the temperature inside the wire is different from the temperature on its surface, this will be necessary anyway.

Just the small point, but you are not limited to a single measurement.

A bit more context would be helpful.

5. Jun 18, 2013

### physicsEEprob

I think I'll go with the infrared thermometer, thanks so much! Also do you think if the wire is steel (it's a guitar string) immersing it in water of a certain temperature for 15 minutes would be long enough to cause the steel to rise or fall to that temperature?
I'm doing my lab on the affect of temperature on the frequency of guitar strings with a uniform applied tension.

6. Jun 18, 2013

### sophiecentaur

Why not measure the resistance of the guitar string? The resistance-measuring circuit need not interfere with the vibration measurement. The temperature coefficient of resistance is well known for most alloys of steel and electrical measurements are very convenient to make.

7. Jun 19, 2013

### Staff: Mentor

The guitar string will approach the temperature of water quickly - probably within seconds. I thought you were sending some current through the wire, otherwise I don't see why it should have a temperature different from the environment.
I guess the frequency measurement should be done without water and with a dry string, right?

8. Jun 19, 2013

### sophiecentaur

The frequency of oscillation of a guitar string in water will be different from that in air and it will be damped considerably if you want to find a good resonance max. Why not keep it in a box (of air) with a fan heater? That way, you could measure the temperature electrically and get a good, representation of the likely behaviour of a guitar string when on a real instrument?

Time for a re-appraisal of your plan, I think - now you've had a number of inputs from PF. A lot of us have wide experience of 'doing experiments' and we don't BS in this department.