Question on the effects of size of bulb on thermomters

In summary, the conversation discusses the effects of increasing the size of a liquid-in-glass bulb, with a focus on the changes in time taken to measure temperature and the need to change the scale markings on the thermometer. The group agrees that the diameter of the bore should be in direct proportion with the increase in the bulb to maintain the scale, and that increasing the radius of the bulb will also affect the volume of the bore. The conversation also briefly mentions the potential increase in manufacturing cost as another effect of increasing the size of the bulb.
  • #1
MforceXXII
9
0
1. Hi, I've got this question that's asking for the effects of increasing the size of the liquid -in-glass bulb. I think they're asking for at least 3 points. 3. L think its supposed to accentuate the increase in volume of the liquid, and it increases the time taken to measure the temperature. Are these correct?Thanks for all your help!
 
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  • #2
Would you conserve or change the graduations on the thermometer, and if so, why?
 
  • #3
I think the graduation and scale should remain the same.
 
  • #4
Why do you think so?
 
  • #5
wait... if they remain the same, then the scale would be wrong. so, the scale should change, to maintain the correctness of the thermometer.
 
  • #6
So... Any idea what the effects would be?
 
  • #7
I agree that if we change the bulb volume this should affect the time for temperature changes to be registered. That's effect 1.

You agreed the need to change the scale markings to deal with the increased volume of liquid. That's effect 2.

By the way, any idea how we could increase the size of the bulb but keep the scale markings identical?

There are obvious changes such as a change in the mass, centre of gravity, and inertial moment of the thermometer, but these do not seem particularly relevant.
 
  • #8
I think if you wanted to keep the scale, what you could do would be to increase the diameter of the bore. Therefore, the diameter of the bore should be in direct proportion with the increase in the bulb, to keep the scale.
 
  • #9
Therefore, the diameter of the bore should be in direct proportion with the increase in the bulb

Let's be clear about this. If I double the radius of the bulb, do I double the radius of the bore?
 
  • #10
I'm would think so...
makes sense i suppose.
 
  • #11
If I double the radius of the bulb, by how much does the volume of the bulb increase?

If I double the bore radius of the tube, by how much do I increase the internal volume for a given length of tube? (We want to keep the temperature graduations the same distance apart).
 
  • #12
What's point three?
 
  • #13
What's point three?

Would you like to suggest one? I can think of loads but I'm not sure the OP wants them.
Increased manufacturing cost would be one example!
 
  • #14
Carid said:
Would you like to suggest one? I can think of loads but I'm not sure the OP wants them.
Increased manufacturing cost would be one example!

The keyword is "effect"--"what's the effect?"

I was thinking of three characteristics of a larger volume: dV/dT, thermal mass, and thermal resistance. The last two have the same effect.
 
  • #15
Phrak said:
The keyword is "effect"--"what's the effect?"

I was thinking of three characteristics of a larger volume: dV/dT, thermal mass, and thermal resistance. The last two have the same effect.

Just wondering, What's that same effect. Longer time to measure to measure temperature?
 
  • #16
MforceXXII said:
Just wondering, What's that same effect. Longer time to measure to measure temperature?

Yes, the amount of time. Greater thermal mass; greater time. Greater thermal resistance; greater time.
 
  • #17
i agree that the volume of the bore should be proportional to the volume of the bulb to keep the same scale. However if you double the radius of the bulb, the volume wil grow 8fold.
If you want the volume of the bore to grow proportionally it will need a radius 8^(1/2) bigger since the volume of a sphere is r^3*pi*(4/3) and the volume of a cilinder pi*r^2*h
 

1. How does the size of bulb affect the accuracy of thermometers?

The size of the bulb on a thermometer can affect its accuracy by changing the volume of air inside the bulb. This volume of air affects the expansion and contraction of the liquid inside the thermometer, which is what measures the temperature. A larger bulb will have more air and can result in a slower response time and less precise readings.

2. Can a larger bulb on a thermometer lead to higher or lower temperature readings?

A larger bulb on a thermometer can potentially lead to higher temperature readings due to the increased volume of air inside. This can cause the liquid inside to expand more, resulting in a higher reading. However, other factors such as the material of the bulb and the accuracy of the thermometer can also play a role in temperature readings.

3. Is there an ideal size or shape for a thermometer bulb?

There is no one ideal size or shape for a thermometer bulb as it can vary depending on the specific use and design of the thermometer. In some cases, a larger bulb may be needed for better accuracy, while in others a smaller bulb may be preferred for faster response time. It is important to consider the intended use and calibrate the thermometer accordingly.

4. How does the size of the bulb affect the sensitivity of a thermometer?

The sensitivity of a thermometer is affected by the size of the bulb because it determines the amount of liquid that can expand and contract in response to temperature changes. A larger bulb will have a larger volume of liquid, leading to a more gradual change in temperature readings and therefore, lower sensitivity. A smaller bulb will have a smaller volume of liquid, resulting in a faster response time and higher sensitivity.

5. Are there any other factors besides bulb size that can affect the accuracy of thermometers?

Yes, there are other factors besides bulb size that can affect the accuracy of thermometers. These include the material of the bulb, the type of liquid used, and the calibration of the thermometer. It is important to consider all of these factors when using a thermometer and to regularly calibrate it to ensure accurate readings.

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