exam model answers Flashcards
Comment on precision (sig fig consistency)
Repeat reading, enough results, look for inconsistent intervals between readings.
Making results more accurate
Parallax error (record at eye level), fiducial markers as reference points, set square to make sure rulers are vertical, averages to reduce random error.
Absolute uncertainty
The uncertainty from the measuring device.
Uncertainty of repeat readings
Uncertainty = half the range of the repeats. Data = mean ± uncertainty.
Percentage uncertainty
Absolute uncertainty / reading * 100.
Accurate
Near the true value.
Precise
Results are grouped together.
Compounding uncertainties
Convert absolute uncertainty to percentage uncertainty, combine the uncertainties, convert back to absolute uncertainties (multiply by value).
Compound uncertainty rules
Multiplying/dividing ADD THE UNCERTAINTIES. Powers MULTIPLY BY EXPONENT.
Systematic error
Fault with equipment (e.g. zero error).
Random error
Due to human error (e.g. human reaction time).
Reading of a micrometer
Read the first two digits off the barrel (e.g. line above and below is 0.5mm). Read the value that lines up with the horizontal line on the thimble and add this to the previous value.
Reading of a vernier caliper
Read off the first two numbers (e.g. 0.8 by looking at where the second scale begins). Third number is how many notches along until the two lines completely line up.
Resolution of a vernier caliper
0.05mm.
Resolution of a micrometer
0.01mm.
Resolution
The smallest division on an instrument.
Why take means
To reduce the effect of random errors and spot anomalies.
Error
An error is the difference between the (measured) result and the true value.
Uncertainty
An uncertainty is the interval/range in which the (true) value can be considered to lie.
Reasons for uncertainty
Instrument resolution, the way the measurement is made (parallax error, reaction times, zero error), a measured constant not being constant.
How to ensure accurate results
Check for zero error, measure dimensions in multiple places, measure for multiple objects then divide by the number (reduces uncertainty).
How is light emitted?
There are electron transitions between energy levels in the atoms. When electrons return to a lower level, they emit energy in the form of photons.
Cathode ray oscilloscope construction
Electron gun, deflection system, and screen.
Cathode ray oscilloscope uses
Measuring voltage, measuring frequency, looking at phase difference.
Show a graph is a 1/x curve
Plot y against 1/x, it should be a straight line through the origin.
