TNT Posted October 23, 2010 Report Share Posted October 23, 2010 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 Reply Link to post Share on other sites More sharing options...
dessskris Posted October 23, 2010 Report Share Posted October 23, 2010 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. Reply Link to post Share on other sites More sharing options...
TNT Posted October 23, 2010 Author Report Share Posted October 23, 2010 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?? Reply Link to post Share on other sites More sharing options...
dessskris Posted October 23, 2010 Report Share Posted October 23, 2010 why would you round it off to nearest cm? 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. 1 Reply Link to post Share on other sites More sharing options...
timtamboy63 Posted October 23, 2010 Report Share Posted October 23, 2010 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 ± 0.5cmHowever, 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 ± 0.005cmHope this cleared things up Also, when you get around to adding, subtracting, dividing and multiplying uncertainties in labs, check out 2 Reply Link to post Share on other sites More sharing options...
fridis Posted February 20, 2011 Report Share Posted February 20, 2011 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) Reply Link to post Share on other sites More sharing options...
mariemarie Posted March 24, 2012 Report Share Posted March 24, 2012 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! Reply Link to post Share on other sites More sharing options...
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