## IB Physics Glossary

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## R |
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## Radioactive decay occurs when a nucleus emits an $$\alpha$$-particle/ $$\beta$$-particle/ $$\gamma$$-particle /ionizing radiations. The process is random and spontaneous since it is unknown when a nucleus will decay. The activity is proportional to the number of undecayed nuclei. The nucleus becomes more (energetically) stable. There is a constant probability of decay. The activity/number of unstable nuclei in sample reduces by half over every half-life. It is not affected by temperature/environmental conditions. | |

## Radioactive decay lawis written as an exponential decay function $$N=N_0 e^{-\lambda t}$$ N: #nuclei at time tN: initial number of nuclei_{0}$$\lambda$$: the decay constant - probability of a decay per unit time t: time Note $$A = - \frac{dN}{dt}= \lambda N$$ or $$A = A_0 e^{-\lambda t}$$ where $$A_0 = \lambda N_0$$ A: activity at time tA _{0}: initial activity of sample$$\lambda$$: the decay constant - probability of a decay per unit time t: time | |

## 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. | |

## Rayleigh Criterion for images of two wave sources to be just resolved the maximum of one diffraction pattern is coincident with the first minimum of the other. (d)
The minimum anglular separation in the diffraction pattern, $$\theta_{min}$$ for two objects to be resolved is given by $$\theta_{min} = \frac{\lambda}{b}$$, for single slits of width b;$$\theta_{min} = 1.22 \frac{\lambda}{b}$$, for circular apertures of diameter b.If two objects at a distance r from the pupil/telescope, separated by distance s, are just resolved then, since $$s=r \theta$$, we can write $$1.22\frac{\lambda}{b} = \frac{s}{r}$$ which can be used to solve typical problems on resolution. | |

## Resisitvity can be found from the resisitivity equation $$R = \frac{\rho L}{A}$$, where R is the resitance, $$\rho$$ is the resistivity, L is the length and A is the cross-sectional area, $$A=\pi r^2=\pi \frac{d^2}{4}$$. << Simulation >> | |

## Resistance is the ratio of voltage to current, $$R =\frac{V}{I}$$. (d) | |

## Resistance combinations occur when resistances or components are placed in series and/or in parallel combinations. The main differences between the two types of combinations are
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## Resonance occurs when an object is forced to vibrate at its natural frequency with a very large increase in amplitude. (d) Resonance is the opposite to damping. If external driving frequency, f, equals to the natural frequency, f, then _{0}f = f or _{0}f/f, and resonance occurs._{0} = 1Notice the resonance amplitude decreases with damping, and the natural frequency decreases. | |

## rms voltage or current equals $$\frac{1}{\sqrt 2}$$ times the peak voltage or current. (s)
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