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How to do uncertainties in biology?

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For lab reports in bio, for the uncertainty is it half the smallest unit used for measurement? For example, if I use cm and so the smallest unit is 1cm. Then is the uncertainty +/-0.5cm? Please can someone tell me how to do the uncertainties. Thx

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I think you should refer to the uncertainty written on the apparatus used's manufacturer label. if it is not there, I think you should take a look at the scale thingy if the apparatus is graduated. if the smallest is 1 mm, then the uncertainty would be 0.5 mm, I believe. like you know, there are 10 lines shown between 1 cm and 2 cm for example.

that is what I know from Physics, though. I assume that it would be the same for Biology since they are both Group 4 subjects.

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I think you should refer to the uncertainty written on the apparatus used's manufacturer label. if it is not there, I think you should take a look at the scale thingy if the apparatus is graduated. if the smallest is 1 mm, then the uncertainty would be 0.5 mm, I believe. like you know, there are 10 lines shown between 1 cm and 2 cm for example.

that is what I know from Physics, though. I assume that it would be the same for Biology since they are both Group 4 subjects.

The smallest of the ruler is 1mm but I rounded it to the nearest cm.

So does that mean I put +/-0.5cm as my uncertainty??

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:S why would you round it off to nearest cm? :confused: I think yes the uncertainty would be +/- 0.5 cm then, but I am not so sure. I highly recommend you to ask your Bio teacher about this.
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It depends on the accuracy of your measuring instrument. Assuming no uncertainty is given on the instrument, here's what you'de do:

Say your reading was 5cm. The smallest scale is centimeters, and half of 1cm is 0.5cm. Hence, your uncertainty is 0.5cm. It is written as:

5cm ± 0.5cm

However, if your reading was 5.32cm, your smallest unit is 0.01 centimeters. Half of this unit is 0.005 cm. and hence your uncertainty is 0.005cm.

Written as:

5.32cm ± 0.005cm

Hope this cleared things up :confused:

Also, when you get around to adding, subtracting, dividing and multiplying uncertainties in labs, check out

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According to my lovely chem book (pearson baccalaurete) there is also a difference in how you calculate uncertainty depending on the instrument used. If it is an analogue instrument such as reading of the scale of a measuring cylinder or ruler, the uncertainty is +/- half the smallest unit. But if it's a digital measurement such as a stop watch or digital scale, it's twice as much (+/- 1 of the smallest unit)

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How would one calculate an uncertainty for light intensity. I am using the formula WATTS/4π(0.1)^2. Where 0.1 is the distance of the light from the object which i measured with a ruler and than converted to meters. So wouldn't my uncertainty for my ruler be +/- 0.5cm but what would my uncertainty for my WATTS light bulb be and for my light intensity in total??? I am really confused, any help will be greatly appreciated!

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