IB Physics Glossary

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B

Bacquerel

, Bq, is the SI unit of activity for radioactive sources. It is equivalent to a count or disintegration per second. The activity is measured, typically, with a Geiger-Muller (GM) tube.
 Keyword(s): 7.2

Beta decay

$^A_ZX \rightarrow~{}^{A}_{Z+1}Y + ^{0}_{-1}\beta + ^{0}_{0}\bar{\nu}$

or

$^A_ZX \rightarrow~{}^{A}_{Z+1}Y + ^{0}_{-1}e + ^{0}_{0}\bar{\nu}$.

Where X is the parent nucleus, Y is the daughter nucleus, A is the number of nucleons and Z is the number of protons.
An example decay is
$^{90}_{38}Sr \rightarrow~{}^{90}_{39}Y + ^{0}_{-1}\beta + ^{0}_{0}\bar{\nu}$.

Properties of beta particles include
• continuous energy spectrum
• -1 charge
• relatively light
• moderately ionizing
• moderate range in air (cm to m)/medium penetration
• can be blocked by a few mm of aluminum or thin lead sheets
• deflected by magnetic-fields and electric-fields (in direction opposite to alpha particles)

 Keyword(s): 7.2

Binary to decimal conversion

for a five bit-number
$b_4 b_3 b_2 b_1 b_0$

the decimal equivalent is

$b_4 \times 2^4 + b_3 \times 2^3 + b_2 \times 2^2 + b_1 \times 2^1 + b_0 \times 2^0$.

An example is the binary number $10101$ which in decimal is

$1 \times 2^4 + 0 \times 2^3 + 1 \times 2^2 + 0 \times 2^1 + 1 \times 2^0 = 21$.

 Keyword(s): 14.1

Binding energy

is the energy required to assemble a nucleus or to separate the nucleus into its individual components/nucleons. (d)

The binding energy per nucleon is the total binding energy for a particular nucleus divided by the number of nucleons contained in the nucleus.

For energy to be released in a nuclear reaction, fusion or fission, the binding energy must increase.

Image taken from http://www.smsec.com/en/nucl/07_1.htm
 Keyword(s): 7.3

Blind spot

is a region where the optical nerve leaves the retina which does not contain rods or cones.
 Keyword(s): A1

Brewster's law

When the angle of incidence equals Brewster's angle, the reflected and the refracted rays are perpendicular to each other. The reflected ray becomes completely horizontally plane-polarized.

$n=\tan \phi$
 Keyword(s): 4

C

Capacitance

is the ratio of charge to potential difference or voltage,

$C=\frac{Q}{V}$.

Its units are Farads.
 Keyword(s): 11

CCD

is a charged coupled device such that the amount of charge that builds up on one of its pixels is proportional to the light intensity falling on the pixel.
The photoelectric effect is responsible for conversion of photons energy to electron energy.
 Keyword(s): 14.2

CCD resolution

is possible if the size of an image covers at least two pixels.
 Keyword(s): 14.2

CD/DVD pit depth

is given by $d = \frac{\lambda}{4}$where $\lambda$ is the wavelength of the laser for the CD/DVD reader.The distance corresponds to a total additional distance of $\frac{\lambda}{2}$ travelled by the laser light at a pit-land interface (corresponding to binary 1).
DVDs (shorter pit length and double layers) have about 7 times the storage capacity of CDs. Changing or reducing the laser wavelength can increase the resolution, by decreasing $\theta= 1.22 \frac{\lambda}{b}$, thus allowing more pits and therefore greater storage capacity. Bluray technology uses shorter wavelength laser light.
 Keyword(s): 14.1

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