Practical 1- Measurement Of The Density Of Solids Flashcards
What apparatus do we need?
-Solid of choice
-30cm rules
-Vernier callipers
-Balance
Resolution
The ‘fineness’ which an instrument can be read to
30cm ruler resolution
+- 0.1cm
Vernier calipers resolution
=-0.01mm
Balance resultion
0.1g
Density equation
P = m
—
V
How do we know what the absolute uncertainty is?
The smallest measurement the measurer does
What do we call the uncertainties involved in this experiment?
Absolute uncertainties
How do we calculate % uncertainty?
Absolute uncertainty
—————————- X100
Measurement
Parallax uncertainty
Looks like a different number when lined up in different places
What’s the phrase for a number looking different when lined up in different places?
Parallax uncertainty
What % uncertainty do we want to be below and why?
5%, for reliability
How could you describe a % uncertainty that’s incredibly small?
Almost negligible - insignificant and not even worth considering
Negligible
Not even worth considering; insignificant
What do we do to calculate the % uncertainty in density?
Add up the % uncertainties (always add!)
What might we have to do to some of the % uncertainties when adding them together?
For example, the radius is squared in the volume formula, therefore we have to multiply it by 2
Method of calculating % uncertainty in density
- Add up the % uncertainties (length, mass and radius, remembering to multiply the radius by 2 as it was squared in the volume formula!)
- Answer divided by 100, multiplied by the density itself, giving us the answer to one significant figure
Do we involve the % uncertainties when working out the density?
No, just the figures as usual
To how many significant figures do we want the % uncertainty for the density?
1
How can the radius of a sphere be accurately calculated?
Using vernier calipers
How do we calculate the absolute uncertainty from the percentage uncertainty?
Percentage uncertainty of answer
