1. Physical Quantities and Units Flashcards
What is a physical quantity?
A physical quantity is a quantity that can be measured.
What are the constituents of a physical quantity?
A physical quantity consists of numerical magnitude (value) and a unit.
What is the SI base unit for mass?
The SI base unit for mass is the kg - kilogram.
What is the SI base unit for length?
The SI base unit for length is the m - metre.
What is the SI base unit for time?
The SI base unit for time is the s - second.
What is the SI base unit for current?
The SI base unit for current is the A - Ampere.
What is the SI base unit for Temperature?
The SI base unit for temperature is K - Kelvin.
What causes Random Errors in measurements?
Random Errors when taking measurements, are a result of uncontrollable factors; such as environmental conditions.
How do Systematic Errors arise when taking measurements?
When taking measurements, Systematic Errors arise from the use of faulty instruments or from flaws in the experimental method.
Explain the effects of Random Errors when taking measurements.
Random Errors when taking measurements, produce an effect on the Precision of the measurements taken, resulting in a wider spread of values about the mean value.
Explain the effects of Systematic Errors when taking measurements.
Systematic Errors when taking measurements result in the readings produced being on either side of the true value; either greater or less than the true value. This is due to the Accuracy having been affected.
The effect on accuracy is because the error is repeated every time the intstrument or techniques is used.
How are Random Errors reduced?
Random Errors are reduced by repeating measurements several times and calculating an average from them.
How are Systematic Errors reduced?
Systematic Errors, when taking measurements, are reduced by recalibrating instruments, or correcting and/or adjusting the technique applied.
What is precision, when taking measurements?
When taking measurements, Precision, is how close the measured values are to each other.
If a measurement is repeated, they are described as precise when they are very similar, or the same as each other.
What is accuracy, when taking measurements?
When taking measurements, Accuracy, is how close a measured value is to the true value.
This can be increased by repeating measurements and finding an average
What is the uncertainty in a reading, when taking measurements?
When taking measurements, the uncertainty in a Reading is ±half the smallest division.
What is the uncertainty in a measurement, when taking measurements?
When taking measurements, the uncertainty in a measurement is ± at least 1 the smallest division.
What is the uncertainty in repeated data, when taking measurements?
When taking measurements, the uncertainty in repeated data is ± half the range
What is the uncertainty in digital readings, when taking measurements?
When taking measurements, the uncertainty in digital readings is ± the last significant digit unless otherwise qouted.
What is the maximum uncertainty when taking measurements?
When taking measurements, the maximum uncertainty is ± half the smallest division.
How are uncertainties combined in addition and subtration?
In addition and subtraction, uncertainties are ALWAYS added together.
These are the uncertainties of the involved terms.
Even in addition, uncertainties are only added.
What is the formula for the combining of uncertainties in addition and subtraction?
dx = dy + dz
Where these are absolute uncertainties.
**Uncertainties are always ADDED
Absolute values =
x = y + z
or
x = y - z
What is the absulute uncertainty?
The absolute uncertainty is the actual uncertainty of a number. That is, Absolute uncertainty is dx in x±dx.
What is the formula for the calculation of fractional uncertainty?
The formula for fractional uncertainty is:
Fractional Uncertainty = Absolute uncertainty / True value
i.e dx/x
What are the 7 Base Quantities?
Quantities from which every other can be derived.
The 7 base quantities are:
1. Mass
2. Length
3. Time
4. Current
5. Temperature
6. Amount of substance
7. Light intensity
Knowledge of the first 5 is necessary according to the syllabus.
When is an equation homogeneous?
An equation is homogeneous if all the terms have the same base units.
As a result it is checked by expressing all the terms in an equation in terms of their base units, which, are displayed in square brackets
If an equation is not homogeneous it is wrong/incorrect.
However, an equation can be homogeneous but still be incorrect due to what?
An equation can still be incorrect even while it is homogeneous due to:
1. Addition of an extra (incorrect term)
2. Elimination of (necessary) terms
3. Wrong coefficient
Experiments were done to check for and get accurate equations.
What is the multiplying factor of the prefix, Tera-, symbol, T?
The multiplying factor of the prefix, Tera-, is 10¹².
To add a prefix to an SI unit, we divide by the multiplying factor.
What is the multiplying factor of the prefix, Giga-, symbol, G?
The multiplying factor of the prefix, Giga-, is 10⁹.
To add a prefix to an SI unit, we divide by the multiplying factor.
What is the multiplying factor of the prefix, Mega-, symbol, M?
The multiplying factor of the prefix, Mega-, is 10⁶.
To add a prefix to an SI unit, we divide by the multiplying factor.
What is the multiplying factor of the prefix, kilo-, symbol, k?
The multiplying factor of the prefix, kilo-, is 10³.
To add a prefix to an SI unit, we divide by the multiplying factor.
What is the multiplying factor of the prefix, deci-, symbol, d?
The multiplying factor of the prefix, deci-, is 10⁻¹.
To add a prefix to an SI unit, we divide by the multiplying factor.
What is the multiplying factor of the prefix, centi-, symbol, c?
The multiplying factor of the prefix, centi-, is 10⁻².
To add a prefix to an SI unit, we divide by the multiplying factor.
What is the multiplying factor of the prefix, milli-, symbol, m?
The multiplying factor of the prefix, milli-, is 10⁻³.
To add a prefix to an SI unit, we divide by the multiplying factor.
What is the multiplying factor of the prefix, micro-, symbol, µ?
The multiplying factor of the prefix, micro-, is 10⁻⁶.
To add a prefix to an SI unit, we divide by the multiplying factor.
What is the multiplying factor of the prefix, nano-, symbol, n?
The multiplying factor of the prefix, nano-, is 10⁻⁹.
To add a prefix to an SI unit, we divide by the multiplying factor.
What is the multiplying factor of the prefix, nano-, symbol, n?
The multiplying factor of the prefix, nano-, is 10⁻⁹.
To add a prefix to an SI unit, we divide by the multiplying factor.
Define the distinction between accuracy and precision.
Accuracy is how close the results are to the true value while precision is how close results are to each other.
A dart hitting the bullseye is accurate, but if the rest of the darts thrown are not close to the bullseye, they are not only less accurate than the first dart thrown, but they are also imprecise. At the same time, a group of darts may be nucleated around an inaccurate region but with all the darts close together, the group of darts is precisely thrown.
- Genetally, however, both would be desired in any experiment or activity requiring them.
What is the formula applied in the combining of uncertainties in which the values in question are multiplied of divided.
du/u = dx/x + dy/y + dz/z
In this case, division, or multiplication: ADD FRACTIONAL UNCERTAINTIES.
x, y, and z are the values that were added or subtracted. u is the result of x, y and z. the d added to each letter, eg. du, together with the letter itself, represent the uncertainties of the values.
What is the rule pertaining to constants and powers, when dealing with finding the uncertainties of derived values? [2]
The rule pertaining to constants and powers, when dealing with finding the uncertainties of derived values is that:
**The constant of a value is not considered when calculating uncertainties, however, when a value, x, is to the power a, a becomes a constant to the fractional uncertainty of x, that is, adx/x. **
What is the formula for the percentage uncertainty of a value?
Percentage uncertainty =
absolute uncertainty(dx)/True value(x)
x 100
or just FRACTIONAL UNCERTAINTY x 100
How are vector quantities different from scalar quantities?
Vector quantities are different from scalar quantities in that they have both magnitude and direction, while scalar quantities have only magnitude.
Give 5 examples of Vector quantities.
5 examples of vector quantities are:
1. Velocity
2. Displacement
3. Momentum
4. Force
5. Acceleration
Give 5 examples of Scalar quantities.
5 examples of Scalar quantities are:
1. Distance
2. Speed
3. Energy
4. Time
5. Temperature
What are two methods of adding or subtracting coplanar vectors?
Two methods of adding or subtracting coplanar vectors are:
1. Calculation method
2. Measuring - Scale diagram
The Calculation method includes, Parallelogram diagram or Vector triangle diagram.
How is a vector represented as two perpendicular components?
NOTEBOOK = IN DEPTH + CALCULATION + APPLICATION
This is done by resolving the perpendicular components of a resultant vector. It includes finding the horizontal and vertical forces contributing to the resultant force at an angle.
This can only be done for a vector at an angle, not 90° or 0°.
It’s like working in reverse from the resultant to the components that it is made up of.
What formula is used to resolve the horizontal component of a force?
Fₕ = FCosθ
F - resultant force, at an angle
Fₕ - horizontal component of F
θ - The angle below the line representing F
Remember cos is like close… imagine a laptop
This can be Sinθ when you subtract the angle under the line representing F from 90 degrees, and use that angle, that is, the upper angle.
What formula is used to resolve the vertical component of a force?
Fᵥ = FSinθ
Fᵥ - vertical component of F
F - resultant force, at an angle
θ - The angle below the line representing F
This can be cosθ when you subtract the angle under the line representing F from 90 degrees, and use that angle, that is, the upper angle.
