StudySquare
Units of motion for OCR A-level Physics
This page covers the following topics:
1. Errors in measurement
During experiments, random errors may occur which will affect precision and cause values of measurements to be different from the real values. Random errors can be reduced by repeating a process at least three times and calculating the mean, or by using computers to take measurements to reduce human error by, for example, eliminating the reaction time.
Systematic errors may also occur due to a faulty experimental method, which affects the accuracy of the measurements obtained, as it will make the values be either too great or too small by the same amount every time. Systematic errors can be reduced by calibrating apparatus and taking measurements at eye level to avoid parallax error.
Uncertainties can be calculated to find the range in which the true value of a reading (usually from an apparatus, electronic) or measurement (usually manual) is expected to lie.
uncertainty in a reading = ±(half the smallest division)
uncertainty in a measurement = ±(at least 1 smallest division)
When adding and subtracting data, the absolute uncertainties can be added, whereas when multiplying and dividing the data, the percentage uncertainties can be added.
1
A reading is taken from a thermometer that has the smallest division of 1°C . Calculate the uncertainty of this reading.
The uncertainty for a reading is ±half the smallest division.
The smallest division of a thermometer is 1°C, so uncertainty = ±0.5°C.
±0.5°C
2
An experiment involving timing a free-falling mass using a stopwatch is conducted to calculate acceleration due to gravity. Identify two possible sources of error in this experiment.
Possible answers: incorrectly callibrated scales when measuring the mass, systematic error in ruler when measuring height through which the mass falls, human random error in measuring time.
incorrectly callibrated scales when measuring the mass, human random error in measuring time
3
The speed of a toy trolley going down the ramp is found by measuring the length of the ramp using a ruler and using lightgates and a computer to measure the time, and using the equation for speed. Suggest why using lightgates and a computer to measure time is likely to introduce less error than using a stopwatch.
Using a stopwatch would increase the random error due to reaction time. Therefore, the lightgates and computer are more reliable since they eliminate human error.
Using computer setup would eliminate the reaction time.
4
Suggest a method which could help reduce systematic error.
Possible answers: calibrating apparatus before use, taking measurements at eye level.
calibrating apparatus before use
5
Define random errors.
Random errors are ones which affect precision and cause values of measurements to be different from the real values.
unpredictable errors affecting precision of measurements
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