IB Physics Glossary



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E

Electronvolt

is the work done in moving an electron through a potential difference of 1 volt. (d)

A charge, q, gains kinetic energy q V when it is accelerated through a potential difference V:

q V = \frac{1}{2}m v^2.

Elevator weight

is used to show how the reaction force, between a person standing in an elevator and the floor of the elevator, varies with up/down acceleration of the elevator:

elevator

Note, the actual weight of the person does not change but an increase or decrease in the reaction force produces a change on the weighing scale in elevator.

Emf

or electromotive force, is the total energy supplied by a cell/battery per unit charge as it flows through the cell/battery. (d)

Emissitivity

is the ratio of power emitted (per unit area) by a body to the power emitted (per unit area) by a black body of the same dimensions at the same temperature
or

the ratio of power emitted by a body to the power emitted if it were a black body. (d)

Energy density

is the energy liberated per unit mass of fuel consumed. Its unit is Jkg-1.(d)

Entropy

is a system property that expresses the degree of disorder in the system. 

Equilibrium position

is the position where a particle would remain at rest if not disturbed. (d)

Escape velocity

is the velocity that an object needs at the surface of the planet with sufficient kinetic energy to escape the gravitational attraction of the planet.
v_{esc} = \sqrt{\frac{2GM}{R}} = \sqrt{2Rg}
where G is the universal gravitational constant, M is the mass of the planet, R is the radius of the planet and g is the acceleration due to gravity.

For a Black Hole, the escape velocity equals c, the velocity of light in empty space. The above equation becomes
c= \sqrt{\frac{2GM}{R}}
and
R= R_s = \frac{2GM}{c^2}
where Rs is the Schwarzchild radius.

Explosive collisions

occur when the total kinetic energy of a system increases.

F

Far point

is the most distant point from the eye for which the eye can focus on (assumed to be \infty).

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