## IB Physics Glossary

Browse the glossary using this index

Special | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T |

**U**| V | W | X | Y | Z | ALL

## U |
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## Ultrasound A-scan is an amplitude-modulated scan with information represented as a graph of signal strength against time. | |

## Ultrasound B-scan is a brightness-modulated scan with information represented as levels of brightness. | |

## Ultrasound choice of frequency is selected based on - the resolution or size of smallest object being scanned
- attenuation which increases with frequency
- pulse length.
$$f = 200 \lambda = 200 \frac{c} {d}$$ where c is the speed of sound waves in tissue and d is the depth of the organ/object. | |

## Uncertainties • resulting from measurements are combined under the following rules: addition/subtraction of quantities => add absolute errors If $$y = a \pm b \pm c $$, then $$\Delta y = \pm (\Delta a + \Delta b+ \Delta c)$$. multiplication/division of quantities = add relative/fractional/percentage errors If $$y = a \times b \times c$$, then $$\frac{\Delta y}{y} = \pm (\frac{\Delta a}{a} + \frac{\Delta b}{b} + \frac{\Delta c}{c})$$, or, $$\Delta y(\%)= \pm (\Delta a(\%) + \Delta b(\%) + \Delta c(\%))$$ and $${\Delta y} = \pm y \times (\frac{\Delta a}{a} + \frac{\Delta b}{b} + \frac{\Delta c}{c})$$, or, $$\Delta y= \pm y \times (\Delta a(\%) + \Delta b(\%) + \Delta c(\%))$$. If $$y = a \div b \div c$$, then $$\frac{\Delta y}{y} = \pm (\frac{\Delta a}{a} + \frac{\Delta b}{b} + \frac{\Delta c}{c})$$, or, $$\Delta y(\%)= \pm (\Delta a(\%) + \Delta b(\%) + \Delta c(\%))$$ and $${\Delta y} = \pm y \times (\frac{\Delta a}{a} + \frac{\Delta b}{b} + \frac{\Delta c}{c})$$, or, $$\Delta y= \pm y \times (\Delta a(\%) + \Delta b(\%) + \Delta c(\%))$$. raising quantity to n'th power = multiply relative/fractional/percentage error by n If $$y = a^n$$, then $$\frac{\Delta y}{y} = \pm |n| \times \frac{\Delta a}{a}$$, or, $$\Delta y(\%)= \pm |n| \times \Delta a(\%)$$ and $${\Delta y} = \pm y \times |n| \times \frac{\Delta a}{a}$$, or, $$\Delta y= \pm y \times |n| \times \Delta a(\%)$$. | |

## Unified atomic mass unit (u)is 1/12 ^{th} the mass of a neutral carbon-12 atom. | |

## Uniform acceleration occurs when the acceleration $$a$$ is held constant. Since acceleration is a vector quantity, constant implies a uniform magnitude and direction for the acceleration. The equations of uniform acceleration are $$v=u + at$$ (not given on IB Physics Data Booklet) $$s = \frac{u+v}{2} t$$ $$s=ut + \frac{1}{2} a t^2$$ $$v^2=u^2 + 2 as$$ where u is the initial velocity, v is the final velocity after time t, a is the acceleration and s is the displacement. | |