Physics Lab - Mechanical equivalent of heat

[minidee]

1.) Using the table provided what is the change in thermistor resistance if temperature rises from 21 C to 30C?

The ohm values for resistance are 120810 for 21C and 79,422 for 30C. I just subtracted the two numbers and got -41,388 ohm. I hope that's right!

2.) This lab involves a spool that has a crank on it and also has a string wrapped around it several times with a mass hanging on the edge of the string hanging vertically.

The question asks: Does it matter how many turns of cord surround the spool? Why? I said it does matter because the length of cord wrapped around determines the amount of friction. Is that right?

3.) Does it matter how fast you turn the crank? Why?
I put it does matter because the faster you crank the more revolutions and therefore gets more work done per turn. If turned quickly enough it can make the cord tension vanish. Is there anything I'm missing in this explanation?

4.)Suppose, the cord where it is attached to the post, is under tension during the experiment. Would this lead to error in your measured value of the mechanical equivalent of heat? If so, would you value be too large or too small?

I would say the measured value would affect the heat but I don't know how to explain this. Please help! Thanks! Guys!

 

[minidee]

anyone?

 

[nlightner]

1.) Your calculation for the change in thermistor resistance is correct. As the temperature increases, the resistance decreases because the thermistor's resistance is negatively correlated with temperature. This is due to the fact that as temperature increases, the atoms in the thermistor vibrate more and create more obstacles for the flow of electricity, resulting in a higher resistance.

2.) Yes, it does matter how many turns of cord surround the spool. This is because the length of cord wrapped around the spool affects the mechanical advantage of the system. The more turns of cord, the greater the mechanical advantage, meaning less force is needed to lift the mass. This also affects the amount of friction between the cord and the spool, as you mentioned. More turns of cord may create more friction and affect the accuracy of the experiment.

3.) Yes, the speed at which you turn the crank does matter. This is because the faster you turn the crank, the more revolutions the spool makes, resulting in more work being done per turn. This can also affect the accuracy of the experiment as it may cause the cord to slip or create more friction, as you mentioned.

4.) Yes, if the cord is under tension during the experiment, it could lead to errors in the measured value of the mechanical equivalent of heat. This is because the tension in the cord adds an additional force to the system, which may affect the accuracy of the experiment. The value could be either too large or too small, depending on the amount of tension and how it affects the results. It is important to ensure that the cord is not under tension during the experiment to obtain accurate results.