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Questions and Answers
What is the best practice for reducing human error in experiments?
What is the best practice for reducing human error in experiments?
When performing a division of two measurements, how should uncertainties be treated?
When performing a division of two measurements, how should uncertainties be treated?
In the context of measuring liquids, what is the reason for reading the meniscus at eye level?
In the context of measuring liquids, what is the reason for reading the meniscus at eye level?
Which of the following describes a scalar quantity?
Which of the following describes a scalar quantity?
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What is an example of systematic error in measurements?
What is an example of systematic error in measurements?
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What happens to percentage uncertainty when raising a quantity to a power?
What happens to percentage uncertainty when raising a quantity to a power?
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Which of the following is NOT a reason for using a micrometer over a ruler?
Which of the following is NOT a reason for using a micrometer over a ruler?
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In radiation experiments, how should background radiation be handled?
In radiation experiments, how should background radiation be handled?
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Study Notes
CAIE Physics A-Level - Topic 1: Physical Quantities and Units
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SI Units: Fundamental units used alongside base SI quantities. Made up of:
- Mass (Kilogram, kg)
- Length (Metre, m)
- Time (Second, s)
- Current (Ampere, A)
- Temperature (Kelvin, K)
- Amount of substance (Mole, mol)
- Derived Units: Units for quantities derived from base units using equations. For example, force (F) is kg x m/s² = N (Newton).
- Homogenous Equations: Equations where units on both sides are the same. All valid physics equations are homogeneous.
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Prefixes: Multipliers for SI units.
- Tera (T) = 1012
- Giga (G) = 109
- Mega (M) = 106
- Kilo (k) = 103
- Deci (d) = 10-1
- Centi (c) = 10-2
- Milli (m) = 10-3
- Micro (µ) = 10-6
- Nano (n) = 10-9
- Pico (p) = 10-12
- Converting Units: Example conversion from MeV to Joules: (1eV = 1.6 x 10-19 J). To convert 76 MeV, multiply by 106 eV, and then by 1.6 x 10-19 J/eV.
- Converting kWh to Joules: 1 kWh = 3.6 x 106 J
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Errors and Uncertainties:
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Random Errors: Affect precision, leading to spread about a mean value. Examples include electronic noise.
- Take multiple measurements and calculate a mean
- Use sophisticated equipment (e.g., computers, data loggers, micrometers)
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Systematic Errors: Affect accuracy, causing all results to be too high or low by a constant amount. Examples include zero errors on equipment (balances, scales).
- Calibrate instruments using known values
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Random Errors: Affect precision, leading to spread about a mean value. Examples include electronic noise.
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Uncertainty:
- Absolute Uncertainty: Fixed quantity (e.g., 7 ± 0.6 V)
- Fractional Uncertainty: Uncertainty as a fraction of the measurement (e.g., 7 ±...V)
- Percentage Uncertainty: Uncertainty as a percentage of the measurement (e.g., 7 ± 8.6% V)
- Reducing Percentage Uncertainty: Take larger readings to reduce uncertainty in small numbers.
- Readings vs. Measurements: Readings are single values, measurements are differences between two readings.
- Uncertainty in Readings and Measurements: Involves half the smallest division.
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Combining Uncertainties:
- Addition/Subtraction: Add absolute uncertainties.
- Multiplication/Division: Add percentage uncertainties.
- Precision vs Accuracy: Precision refers to consistency of measurements, accuracy describes closeness to the true value.
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Scalars and Vectors:
- Scalars: Described by magnitude only (e.g., mass, speed, distance).
- Vectors: Described by magnitude and direction (e.g., force, velocity, displacement).
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Description
Test your understanding of best practices in experimental physics. This quiz covers topics such as handling uncertainties, dealing with systematic errors, and the proper techniques for measuring liquids and background radiation. Challenge your knowledge of scalar and vector quantities as well!
