## IB Physics Glossary

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 All categories CategoriesAll categoriesNot categorisedTopic 1: Measurements and uncertaintiesTopic 2: MechanicsTopic 3: Thermal PhysicsTopic 4: WavesTopic 5: Electricity and magnetismTopic 6: Circular motion and gravitationTopic 7: Atomic, nuclear and particle physicsTopic 8: Energy productionTopic/AHL 10: FieldsTopic/AHL 11: Electromagnetic inductionTopic/AHL 12: Quantum and nuclear physicsTopic/AHL 9: Wave PhenomenaTopic/Option D: Astrophysics

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### TOPIC 1: MEASUREMENTS AND UNCERTAINTIES

#### Accuracy

tells us how close the measured value of a quantity is to its true value. An accurate measurement is "close" to a true value. An inaccurate measurement is "far" from a true value.
 Keyword(s): 1.2

#### Derived units

are not fundamental but can be expressed in terms of fundamental units.
 Keyword(s): 1.2

#### Fundamental units

are the most basic units which cannot be expressed in terms of other units. The seven fundamental units are
1. meter (m);
2. second (s);
3. kilogram (kg);
4. Kelvin (K);
5. The Ampere (A);
6. mole (mol);
7. candela (cd).
 Keyword(s): 1.2

#### Log-log plots

are used to find the value of the exponent $$n$$ and coefficient $$a$$ for the general relationship $$y= a x^n$$.
The value of the gradient for the log-log plot equals $$n$$ and $$a= log^{-1}{(\text{y-intercept})}$$.
For example
A linear relationship should have $$n \approx 1$$;
A square-root relationship should have $$n \approx \frac{1}{2}$$;
A quadratic relationship should have value $$n \approx 2$$;
An inverse-square relationship should have value $$n \approx -2$$.
 Keyword(s): 1.2

#### Precision

tells us how consistent repeated measurements are. A precise set of measurements are relatively closer together. An imprecise set of measurements are spread apart.
 Keyword(s): 1.2

#### Proportional relationship

$$y \propto x$$ or $$y = m x$$, occurs when the relationship between $$y$$ and $$x$$ is linear with a zero y-intercept value, that is, a straight line passing through the origin.
The x- and y-error bars may allow a range of values for the y-intercept, because the lines of max & min gradients, thus showing a possible proportional relationship for a best-fit straight line even if its y-intercept value is non-zero. Beware, for the IB, a best-fit line can be any curve which fits the data points. It does not mean the best-fit straight line.
 Keyword(s): 1.2

#### Random error

is a fluctuating error often present in experiments. It is linked to precision: imprecise data => "high" random error; precise data => "low" random error. Repeated measurements do reduce random errors. Sources of random errors can include varying reading/human error and other randomly flucuating factors which cannot be controlled during experiments.
 Keyword(s): 1.2

#### Scalar multiplication

of vectors, changes the magnitude of the vector but not the direction.
For scalar $$a$$ and vector $$\vec{A}$$ with
x- or horizontal component $$A_H=A \cos \theta$$
y- or vertical compnonet $$A_V= A \sin \theta$$
magnitude $$A=\sqrt{A_H^2 + A_V^2}$$

The multiplication $$a \times \vec{A}$$ has magnitude $$a \times A$$.
The division $$\vec{A} \div a$$ has magnitude $$A \div a$$.
 Keyword(s): 1.3

#### Scalar quantities

have magnitude only. Direction or changes in direction have no effect on scalar quantities. Examples include distance, speed, mass and temperature.
 Keyword(s): 1.3

#### Signifiant figures

a rule, the number of significant digits in a result should not exceed that
of the least precise value upon which it depends.
 Keyword(s): 1.2

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