IB Physics Glossary

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, 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.

Beta decay

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


^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)

More info

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.

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

Blind spot

is a region where the optical nerve leaves the retina which does not contain rods or cones.

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