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Physics data present
Physics Autumn Y12
| Question | Answer |
|---|---|
| How to format tables | Gridlines - internal and external (lines on exercise book count horizontally) Columns correctly ordered Columns should have proper headings |
| What is the correct order for columns? | Independent, Dependent, then calculated columns |
| What is the proper heading for a column | Must be consistent. Force (N) is valid Force/N is preferred by Mr Clegg (shows how the units have been removed) |
| What is resolution? | The smallest increment or number of decimal places on an instrument |
| Note with stopwatch precision | The precision of the instrument is not reduced by the reaction time issue: the only thing affected is the data (reduced d.p. to reaction times if single results, but to resolution of instrument if a mean) |
| How many d.p. or s.f. for raw data and processed data | Raw: The same d.p. as the resolution of the instrument Processed: Same SF as the least SF used in calculation This may lead to weird data mismatches, but still correcr |
| How to calculate uncertainty | If single readings taken, should be resolution. Otherwise +- range/2 |
| For all data sets prior to calculations e.g. 9.81, 9.78, 10.61, 9.92 | Remove anomalies from data set |
| What does a horizontal bar above a term mean? | Mean of |
| What s.f./d.p. is uncertainty to and why? (important) | Uncertainty is always to 1 s.f. unless it's a 1, where it becomes 2 s.f. Why: (+- 0.3 goes from 0.25 to 0.35, so has an uncertainty of +- 15%. +- 0.1 goes from 0.05 to 0.15, so has uncertainty of +- 50%) |
| What s.f./d.p. is the mean next to the uncertainty to and why? | Same d.p. as the uncertainty |
| How many d.p. is 0.0005? | 4 |
| What is absolute uncertainty? | The difference between a measured value and the actual value [The uncertainty of unit numbers, not percent (relative uncertainty)] |
| What can absolute uncertainty be affected by (e.g. question is asking the uncertainty of a 2d.p. stopwatch) | Affected by reaction time - reduces d.p. of measured values to account for it. Less manual uncertainty for anticipated events |
| When working with absolute uncertainties, how the uncertainty might change | For adding/subtracting, the uncertainties add together For multiplication/division, use the relative uncertainties, then convert to absolute uncertainty |
| If the last digit on a measuring instrument fluctuates a lot | Ignore it and reduce d.p. |
| e.g. Diameter of wire read to 0.01mm: 3.46, 3.55, 3.42 What is the uncertainty of the radius? | Remember 3.42 could be 3.415 and 3.66 could be 3.555 Remember diameter vs radius Calculated gives +- 0.035, but because there are only 3 measurements, it's difficult to justify such high d.p. Also because so few, better to go +- 0.04 rather than 3 |
| When multiplying and dividing with significant figures | The answer will have the same amount of numbers as the number with the fewest sig figs |
| When adding and subtracting with significant figures | The answer will have the same amount of decimal places as the number with the fewest amount of decimal places This is because (and how you do this for low indices differences) when you line up the digits, go for the left most endpoint |
| What is accuracy? | A measurement result is considered accurate if it is judged to be close to the true value. Property of a single result - either one or a man. Not quantifiable - instead seen as more/less accurate |
| Precision | A quality denoting the closeness of agreement between (consistency, low variability of) measured values obtained by repeated measurements. Can be expressed numerically (because being precise depends on context). Depends on extent of random effects |
| Calculating uncertainty from range | Remember to divide range by 2 |
| When working with relative uncertainty, how to work out number of d.p. of the mean value | Convert to absolute. Work out how many d.p. for the mean value. Copy for value with relative. |
| What do we quote uncertainty to? | Equal to the instrument resolution (except stopwatch) |
| How to work out s.f/d.p of relative uncertainty | It works the exact same as absolute uncertainty - namely 1s.f. unless a 1 |
| Reasonable reaction time | 0.2 - 0.5s |
| Relative uncertainty definition and equation | percentage uncertainty = uncertainty/average value x 100% |
| To nearest second means what in terms of uncertainty | +- 0.5 |
| 6cm length measured by mm ruler | Exam accepts either +- 0.5 or 1 mm. 1mm is better though, because all measuring devices (including digital e.g. weighing scale zeroing) have 2 points of measurement, so +-0.5 x 2. Hence +- resolution |
| How to combine uncertainties when multiplying/dividing | When multiplying/dividing, percentage uncertainties are added (even if dividing). |
| How to combine uncertainties when multiplying/dividing by an integer as well | The integer is perfectly accurate, so does not affect the percentage uncertainty, although it does scale the absolute uncertainty as it should |
| When y = a^n, what is the rule for %uncertainty in y? | % uncertainty in y = n x (%uncertainty of a) n can be less than 1, which reduces uncertainty |
| How to combine uncertainties when adding/subtracting | When adding/subtracting, we can only do it when they have the same unit. Add the absolute uncertainties (even if subtracting) |
| What are wavelengths of light normally measured in | Hundreds of nm |
| e.g. D = A/W. Does increasing accuracy of W increase overall accuracy | Yes, but not by much |
| How is y = mx + c useful? | c = y intercept, so is the initial velocity on a velocity time graph, with m being acceleration. |
| Which axis for independent? | x |
| What do error bars show? | The absolute uncertainty of data |
| Explain finding uncertainty of c and m from a graph | From lobf we can find m and c. Then plot a line of worst fit (steepest or shallowest) by connecting highest/lowest points. Lowf must pass through all error bars though. Either work out diff between lowfs/2 or between lowf and lobf |
| When analyzing graphs with false axis | Careful with y intercept |
| When measuring the diameter of a wire in a practical | Measure multiple different points along wire and take average |
| What happens if your results don't give the lobf the experiment is expecting? | Do an honest lobf, not just fitting the answer |
| 2 resistors. 120 and 500 ohms. % uncertainty in each is 10%. Find total r and uncertainty. | Convert to absolute uncertainty to add together. Comes out to 97 +- 10% |
Created by:
Pyrogearos2