Ib Lab - 04 Errors - Microscope Slide (dc Dpp)

International Baccalaureate Physics

4/PSOW

To Show Errors in Experiments by Measuring the Density of a Microscope Slide with 2 different Sets of Instruments. IB Criteria Assessed Aim: Data Collection, All experiments are done with measuring instruments. No instrument is perfectly accurate - they all have limits to their accuracy. It is important Data Processing that you realise that no experiments give perfect, exact answers. To Criteria Aspect Level assessed 1 2 3 awarded illustrate this you are going to measure the density of a slide with: 1. a precision electronic balance, and a Vernier gauge. 2. then with a lever arm balance and a metre rule. From these 2 sets of measurements you will calculate the density of the slide. One of the experiments is more accurate than the other, but both are imprecise. From now on, all your experimental results will include the uncertainties associated with the measuring apparatus used. (and for HL student, a calculation of ± error in the readings and in the final result).

Pl (a) Pl (b) DC DPP CE

Apparatus: Vernier, metre rule, microscope slide, electronic scale, lever arm balance. Method: 1. Measure the mass of the slide on both the precise and less precise scale. 2. Measure the length, breadth and thickness of the slide with the vernier and then the metre rule. 3. Write all of your measurements in a suitable table of results with a ± uncertainty at the top of each column. Theory:

density =

mass volume

Calculate density using the readings from the metre rule and less precise balance. Repeat this with the readings from the precise scale and the vernier. Compare the precision of these two results. SL Students: Calculate the maximum and the minimum possible value for the density of the slide based upon the precision of the two sets of apparatus. HL Students: Using the uncertainty in the readings, calculate the largest and smallest possible values for the density of the slide. In both cases produce an answer for the density of the slide in the form: Density = ***** g cm-3 ± ** g cm-3 Density = ***** g cm-3 ± ** % All measuring instruments have limits to their accuracies but you can make them less accurate by not using them carefully. It is important that : (a) the balances are at zero before the slide is put on them. (b) you put the slide on the balance; don’t drop it on them. (c) the metre rule is not worn away at one end. In all your future experiments you should always be aware of the importance of using your measuring instruments as accurately as possible.

© 2006 - Mike Dickinson

8266771.doc

International Baccalaureate Physics

4/PSOW

Internal Assessment Marking Form Crit.

Pl(a)

Pl(b)

DC

DPP

CE

Aspects Research Question: Hypothesis: Variables: c. Identifies a focused c. Relates the hypothesis or c. Selects the problem or research prediction directly to the relevant question. research question and independent p. States the problem or explains it, quantitatively and controlled research question, but it where appropriate. variable(s). is unclear or incomplete. p. States the hypothesis or p. Selects some n. Does not state the prediction but does not relevant problem or research explain it. variables. question or repeats the n. Does not state a n. Does not select general aim provided by hypothesis or prediction. any relevant the teacher. variables. Materials / Control of Variables: Collecting Data: Apparatus: c. Describes a method c. Describes a method that c. Selects appropriate that allows for the allows for the collection apparatus or control of the of sufficient relevant materials. variables. data. p. Selects some p. Describes a method p. Describes a method that appropriate that makes some allows for the collection apparatus or attempt to control the of insufficient relevant materials. variables. data. n. Does not select n. Describes a method n. Describes a method that any apparatus or that does not allow for does not allow any materials. the control of the relevant data to be variables. collected. Collecting / Recording Raw Data: Organising / Presenting Raw c. Records appropriate raw data (qualitative Data: and/or quantitative), including units and c. Presents raw data clearly, uncertainties where necessary. allowing for easy p. Records some appropriate raw data. interpretation. n. Does not record any appropriate raw data. p. Presents raw data but does not Aspect 1 includes units, uncertainties, allow for easy interpretation. significant digits n. Does not present raw data or presents it incomprehensibly. Processing Raw Data: Presenting Processed Data: c. Processes the raw c. Presents processed data appropriately, helping data correctly. interpretation and, where relevant, takes into p. Some raw data is account errors and uncertainties. processed correctly. p. Presents processed data appropriately but with some n. No processing of raw errors and/or omissions. data is carried out or n. Presents processed data inappropriately or major errors are made incomprehensibly in processing. Aspect 2 includes uncertainty bars, max / min slopes (HL), axes with labels and units, best fit line drawn Drawing Conclusions: Evaluating procedure(s) Improving the c. Gives a valid and results: investigation: conclusion, based on the c. Evaluates procedure(s) c. Identifies correct interpretation of and results including weaknesses and the results, with an limitations, states realistic explanation and, where weaknesses or errors. suggestions to appropriate, compares p. Evaluates procedure(s) improve the results with literature and results but misses investigation. values. some obvious p. Suggests only p. States a conclusion that limitations or errors. simplistic has some validity. n. The evaluation is improvements. n. Draws a conclusion that superficial or n. Suggests unrealistic misinterprets the results. irrelevant. improvements.

© 2006 - Mike Dickinson

Level ccc 3 ccp 2 ccn 2 cpp 2 ppp 1 cpn 1 cnn 1 ppn 1 pnn 0 nnn 0

Grade

ccc 3 ccp 2 ccn 2 cpp 2 ppp 1 cpn 1 cnn 1 ppn 1 pnn 0 nnn 0

cc 3 cp 2 cn 1 pp 1 pn 0 nn 0

cc 3 cp 2 cn 1 pp 1 pn 0 nn 0

ccc 3 ccp 2 ccn 2 cpp 2 ppp 1 cpn 1 cnn 1 ppn 1 pnn 0 nnn 0

8266771.doc