## IB Physics Glossary

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### C

#### Chandrasekhar core limit

equals 1.4 solar masses for the core of a (super) red giant.

Low mass stars: core mass < 1.4 solar masses
Red giant -> Planetary nebula -> White dwarf
Helium burns and fuses in the core into carbon and oxygen.

High mass stars: core mass > 1.4 solar masses
Super Red Giant -> Supernova -> Neutron star or Black Hole
Silicon burns and fuses in the core into iron.
 Keyword(s): E5

#### Circular motion

occurs under the following conditions:
• the force $F$, and therefore acceleration $a$, and change in velocity $\Delta v$, is directed towards the center of a circle;
• the velocity is perpendicular to the force, $v \perp F$.

Data booklet reference:﻿

﻿$\nu \; = \;\omega r$
$a\; = \;{{{v^2}} \over r}\; = \;{{4{\pi ^2}r} \over {{T^2}}}$
$F\; = \;{{m{v^2}} \over r}\; = \;m{\omega ^2}r$
 Keyword(s): 6.1

#### Coefiicient of voume expansion

$\gamma$, is the fractional change in volume of a substance $\frac{\Delta V}{V}$ per unit degree change in temperature $\Delta T$:
$\gamma = \frac{\Delta V}{V \times \Delta T}=\frac{V_2-V_1}{V_1 \times (T_2-T_1)}$.
The SI unit is K-1.

For problems involving rise in sea level
• height, h, of water can be found from
$h = \frac{Volume}{Area}$
• rise is seal level can be calculated using
$\Delta h = \gamma \times h \times \Delta T$.
 Keyword(s): 8.6

#### Comets

have
a. highly elliptical orbits;
b. large orbital radii beyond planets;
c. orbit are in many different planes. (d)
 Keyword(s): E1

#### Conductive hearing loss

occurs when the air conduction thresholds (middle ear) show a hearing loss but the bone conduction thresholds (cochlea) are normal. Reasons include
1. blockages - build up of wax of fluid;
2. accidents - damaged middle ear or ruptured eardrum;
3. diseases/infection - middle ear bones are prevented from moving;
4. age - bones in middle ear become solidified with age.
 Keyword(s): I1

#### Conductor

﻿A material that allows the flow of electric charge through it.
Conduction is the flow of charge (free electrons) from atom to atom within a material.

#### Constellation

is a pattern of stars, as seen from Earth, which are not close to one another in space. (d)
 Keyword(s): E1

#### Constructive interference

occurs when two waves meet such that the resultant wave displacement is greater than that of the individual waves with path difference $= n \times \lambda$ or phase difference $= n \times 2\pi$. (s)
 Keyword(s): 4.5

#### Coulomb's Law

$F =\left( \frac{1}{4 \pi \epsilon_0}\right) \frac{q_1 q_2}{r^2} = k \frac{q_1 q_2}{r^2}$
where F is the force exerted by particle 1 on particle 2 (and vice versa), k is the Coulomb/electric constant, 8.99 x 109 Nm2C-2, q1 is the charge of particle 1, q2 is the charge of particle 2 and r is the distance between the centres of the particles/charges.

Note $k=\frac{1}{4 \pi \epsilon_0}$, where $\epsilon_0$=8.85×10−12 C2 N−1m−2 is the permittivity of free space. We usually just use k.

We assume the charges are point-like and all the charge is concentrated in the center. An approximation is to assume the separation of the charges, r, is much greater than their radii.

The law is an inverse-square-law, $F \propto \frac{1}{r^2}$.

#### Critical density

is the density which produces a flat universe. In a flat universe the rate of expansion of the universe gradually slows down, asymptotically approaching a zero rate of expansion. (d)
 Keyword(s): E4

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