## IB Physics Glossary

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### P

#### Parallel plates

For parallel plates, of separation d, with a potential/voltage difference ΔV across the plates, the electric field, E, is given by
$E=\frac{\Delta V}{d}$

The electric field is uniform or constant between the plates.

Examples

#### Parsec

is the distance to a star whose parallax angle is 1 arc-second. (d)
 Keyword(s): E3

#### Phase difference

$\phi$, is the difference in phase angle between two oscillations with the same frequency. (d)
 Keyword(s): 4.1

#### Photopic vision

is color vision which occurs at normal light levels. Vision is aided by the three different cone cells, S (for short-wavelengths or blue), M (for medium-wavelengths or green) and L (for long-wavelengths or red).
 Keyword(s): A1

#### Polarization

of light occurs when the direction of the electric field oscillations is in the same plane. (d)
 Keyword(s): 4

#### Potential divider rule

is used to calculate the potential difference which is shared between components, R1 and R2, placed in series:

where $R_1 + R_2$ is the total resistance and E is the emf.

Note

$E=V_{R1}+V_{R2}$

for equal resistances, $R_1=R_2$, the potential difference is shared equally between the resistances

for unequal resistances, $R_1 \ne R_2$, the potentail difference is not shared equally but will be greater across the resistance with highest value.
 Keyword(s): 5.2

#### Potential energy

is a stored form of energy available to do work.
 Keyword(s): 2.3

#### Power

is the rate at which work is done. (d)
 Keyword(s): 2.3

#### Precision

tells us how consistent repeated measurements are. A precise set of measurements are relatively closer together. An imprecise set of measurements are spread apart.
 Keyword(s): 1.2

#### Pressure

is the force per unit area. (d)
 Keyword(s): 3.2

#### Primary colors

are red, green and blue. Mixed together they produce white.
 Keyword(s): A1

#### Principle of Superpostion

when the paths of two waves of the same type coincide, move through each other or cross, the resultant displacement is the sum of the two individual wave displacements at the point. (s)
 Keyword(s): 4.5

#### Progressive travelling wave

transfers energy with no net motion of the medium through which the wave travels. (d)
 Keyword(s): 4.4

#### Projectile motion

• The vertical and horizontal components of velocity, in a uniform field, are independent of each other.
• The vertical velocity follows the equations of uniform acceleration. The horizontal velocity, in the absence of air resistance, remains fixed. The velocity, or total velocity, is the vectorial/Pythagorean sum of the horizontal and vertical velocity components since they are perpendicular to each other: $V =\sqrt{V_v^2 + V_h^2}$.
• In the absence of air resistance, the range of a projectile is independent of mass of projectile. It depends on the horizontal velocity. The range, D, is the maximum horizontal distance traveled by the projectile: $D= V_h \times t$.

• The time of fall is independent of horizontal velocity. It depends vertical height of projectile, $t= \sqrt{\frac{2 \times height}{g}}$ if projectile has no initial vertical velocity component, ie. it is dropped.
 Keyword(s): 9.1

#### Proportional relationship

$y \propto x$ or $y = m x$, occurs when the relationship between $y$ and $x$ is linear with a zero y-intercept value, that is, a straight line passing through the origin.
The x- and y-error bars may allow a range of values for the y-intercept, because the lines of max & min gradients, thus showing a possible proportional relationship for a best-fit straight line even if its y-intercept value is non-zero. Beware, for the IB, a best-fit line can be any curve which fits the data points. It does not mean the best-fit straight line.
 Keyword(s): 1.2

#### Pulsar

is a rotating neutron star. (d)
 Keyword(s): E5

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