Tuesday, 21 January 2020, 7:09 AM
Site: The Science Portal: 21C Science with Style
Course: The Science Portal: 21C Science with Style (21CScience)
Glossary: IB Physics Glossary

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

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 active

substances 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 Motion

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