## IB Physics Glossary

Browse the glossary using this index

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**ALL**

## D |
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## Damping involves a force that is always in the opposite direction to the direction of motion of the oscillating particle/system and the force is a dissapative force which reduces the total energy of the system. (d) | |

## Decay constant, is the probability of a radioactive decay per unit time. at t=t _{1/2}, N=N_{0}/2: after one half-life the number of nuclei halves=> => or => or A shorter half-life indicates a more active sample or a higher value for the decay constant (greater probability for a decay). A a short half-life sample can be measured from the activity-time graph, simply finding the time for the activity to fall by a factor of 2. For a long half-life sample, the activity, A, is measured at the same time as the mass, m, of the sample. We know number of atoms, N = number of moles, n, times Avogadro's constant, N _{A}and number of moles, n = mass in grams, m/atomic mass number, a, therefore Since | |

## decimal to binary conversioncan be completed by dividing by 2 and keeping track of the remainder: an example is 21
which gives 10101. | ||||||||||||||

## Degraded energy is transformed energy which is no longer available to perform useful work. (d) | |

## Derived units are not fundamental but can be expressed in terms of fundamental units. | |

## Destructive interference | |

## Displacement | |

## Doppler effect is the apparent change in the frequency of a wave source due to the relative motion between the wave source and observer. Let = observed frequency = actual wave frequency = speed/velocity of waves in medium (fixed by medium and its properties) = speed/velocity of wave source = speed/velocity of observer For a moving source - stationary observer (change in observed wavelength of source) Use , (decrease in wavelength), if wave source moves towards observer Use , (increase in wavelength), if wave source moves away from observer For a moving observer - stationary source (change in relative speed of waves) Use , , increase in relative speed/velocity of waves (), if observer moves towards wave source. Use , , decrease in relative speed/velocity of waves (), if observer moves away from wave source. For electromagnetic waves where v is the speed of the wave source and c is the speed of electromagnetic waves in a vacuum. | |

## Doppler flow-speed measurements | |