Core Practicals Flashcards
Explain the method to determine ‘g’
Drop an object from rest. Measure time and distance until it reaches the ground. Use suvat to determine g.
How can you graphically determine ‘g’
2s over t^2. Gradient = g
How can you improve accuracy for finding ‘g’?
Use light gates or a trap door for timing rather than a stopwatch, to eliminate human reaction times, which cause a % uncertainty.
What systematic errors are there when determining g?
Air resistance, will cause the measured value of g to be less than the true value.
Explain the method for determining the resistivity of a wire
Set up a wire connected to a cell with a ammeter and voltmeter parallel to the wire.
Measure the length of wire and numerous diameters. Measure voltage and current to calculate resistance - V=IR.
What systematic errors are there when determining the resistivity of a wire?
Heating of wire due to current. Using a small current can minimise this. Resistivity is temperature dependant.
How do you calculate percentage uncertainty?
uncertainty/mean value x 100%
Explain what graph you may plot for determining resistivity.
R against l and gradient = ρ/A
Define Validity
A measurement is valid if it measures what it is supposed to
Define Systematic Error
Introduces the same error to all measurements. Includes zero errors.
Define Random Error
Reading might be too small or large by the same amount.
Explain how you would combine uncertainties
If adding data: add absolute uncertainties
If multiplying data: add percentage uncertainties
Raised to a power: Multiply U% by power
Define error
An error is the difference between the (measured) result and the
true value
Define uncertainty
An uncertainty is the interval/range in which the (true) value can
be considered to lie
Give two reasons why a measurement may have an uncertainty.
- resolution of instrument
- zero error
- parallax error
- reaction time
What is the absolute uncertainty of micrometer screw gauge
± 0.01mm
What is the absolute uncertainty of vernier callipers
± 0.1mm
Comment on the student’s suggestion of using a data logger rather than a stopwatch.
Using the stopwatch there would be reaction time. The uncertainty in the measurement of the time is larger with the
stopwatch than with the data logger. Light gates are difficult to use with a pendulum bob. Timing multiple swings (with stopwatch) reduces %U
Explain how the student could reduce the uncertainty in the measurement of the diameter.
Measured diameter in multiple places / orientations and calculate a mean. Calculating a mean reduces the effect of random error.
Describe how to determine the corrected count rate from the source
Remove the source and record background count for specified time and subtract from equivalent quantity. Divide by time to give a count rate per second.
Describe how the diffraction grating is used and the measurements that should be taken.
set up diffraction grating at right angles to light from laser/ parallel to screen. measure the distance between the diffraction grating and the screen. measure the distance between 1st order images on the screen
Explain how plotting a graph should improve result
Graph enables an average result to be taken. Graph will show anomalies. Graph will show if resistance changes
List any apparatus required when determining the viscosity of a liquid
Measuring cylinder, liquid, ball bearing, markers, micrometer, metre ruler, timer.
Identify the main source of uncertainty when determining the viscosity of a liquid
Terminal velocity not reached. Reaction time. Temp of liquid not constant. Measurement of diameter. Parallax error. Measurement of distance.
Describe what physicists mean by the term accuracy
Accuracy is a measure of how close a measured/calculated value is to the true value
Describe what physicists mean by the term precision.
Precision is the consistency of values obtained by repeated measurements
