## 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

## O |
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## Ohm's law states that current is proportional to voltage, at constant temperature, $$I \prop V$$. (d) The graph should be a straight line passing through the origin. For non-ohmic conductors current is not proportional to voltage, $$I \cancel{ \prop} V$$. The graph is non-linear. Examples of non-Ohmic conductors include - filament light bulbs
as $$I \uparrow, T \uparrow, R \uparro \Rightarrow$$ gradient is not constant, or, as $$I \downarrow, T \downarrow, R \downarrow \Rightarrow$$ gradient is not constant.
Typical graphs can be y-axis: I, x-axis: V, $$R \uparrow \Rightarrow \frac{V}{I} \uparrow \Rightarrow$$ gradient decreases;
y-axis: V, x-axis: I, $$R \uparrow \Rightarrow \frac{V}{I} \uparrow \Rightarrow$$ gradient increases. - thermistors
NTC (negative temperaure coefficient): $$T \uparrow \downarrow R \downarrow \uparrow$$;
PTC (positive temperature coefficent): $$T \uparrow \downarrow R \uparrow \downarrow$$. - Light dependent resistors (LDRs)
brightness $$\uparrow \downarrow$$, $$ R \downarrow \uparrow$$;
- Strain gauge
a variation in strain of a material (deformation per unit length due to the effect of an applied load/mass) produces a variation in electrical resistance of material
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## One Mole of substance has as many molecules as there are atoms in 12g of Carbon-12. (d) | |

## Oppenheimer-Volkoff limit is approximately 2-3 solar masses for mass of core for Super Red Giant; for core masses < 2-3 solar masses (above 1.4 solar masses) $$\rightarrow$$ Neutron star for core masses > 2-3 solar masses $$\rightarrow$$ Black hole. | |

## Optically activesubstances rotate the plane of polarization of the incident light. The amount of rotation may depend on the concentration of the substance/solution and the amount/length/thickness. | |

## Orbital Motionoccurs when the gravitation provides the centripetal force for circular orbital motion: $$F = G \frac{Mm}{r^2}=\frac{mv^2}{r}$$. | |