# The Definition Dictionary

Definitions are probably the most important part of Physics for the FRCA examinations. Not only do they give you something to hang your answer on, and sometimes gives you the answer to further questions, They also look amazing in a VIVA if you can give a punchy, accurate definition. That is what this page is for! All in alphabetical order!

## A

Absolute Humidity

The mass of water vapour (Grams) present per volume of air (Cubic Metre).

Absolute Zero

Absolute zero is defined as the temperature at which all molecular movement stops

#### Accuracy

The ability of a measured value to equal the actual value

Ampere

‘Unit of Electrical Current; 1 ampere = 1 Coulomb/second.’

Amplifier

An amplifier is a device which increases the amplitude of an electrical current/signal using a power supply

## B

Beer’s Law

‘The absorption of light is proportional to the concentration of the gas through which the light is travelling.’

The Bernoulli Principle

An increase in velocity of a moving fluid results in simultaneous decrease in its pressure (and visa versa)

Boyle’s Law

‘At a constant temperature, the volume of a fixed amount of gas is inversely proportional to its pressure.’

## C

Candela (a measure of light – cd)

One Candella = The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 5.4×1014 hertz and that has a radiant intensity in that direction of 1/683 watt per square radian.

Capacitor

‘Electrical device which stores electrical charge.’

Charles’ Law

‘At a constant pressure, Volume of a fixed amount of gas is proportional to its absolute temperature.’

Conductance

‘Conductance is the ability of the material to allow the flow of electrical charge.’

Coulomb

‘Unit of Electrical Charge; 1 Coulomb = 6.24×10ˆ18 electrons.’

Current Density

Current density is the current flowing divided by the area it flows through.

## D

Damping

Damping is the ability of an object to resist oscillation in response to a force being applied to it.

Dew point

Temperature below which water will begin to condense out of air. (e.g. relative humidity reaches 100%)

Diffusion

Movement of a substance/solute from an area of high concentration to that of a low concentration

Diodes

Diodes are electrical components that allow current to flow in one direction only.

Doppler Effect

The change in apparent wavelength of a wave when the observer is moving relative to the wave source.

## F

‘One Farad is the ability of a capacitor to store one coulomb of charge when a potential difference of one volt is applied across it’.

## G

Gay Lussac’s Law

‘At constant volume, Pressure of a fixed volume of gas will increase in proportion to absolute temperature.’

Gauge Pressure

Gauge (or relative) pressure is defined as the absolute pressure minus the reference pressure (usually, but not always atmospheric pressure).

## H

Heat

Type of energy that moves between two objects due to a difference in temperature

Heat Capacity

The amount of heat energy required to increase the temperature of an object by one Degree Centigrade/Kelvin

Humidity

The amount of water (vapour) present within a gas (usually air).

## I

Inductor

‘A component which opposes the flow of current by creating an electromotive force.’

## K

Kelvin

One Kelvin = 1/273.16 of the thermal energy of the triple point of water.

Kilogram

One Kilogram = The mass of the international kilogram prototype in Pavillon de Breteuil, Sévres, France.

## L

Lambert’s Law

‘The absorption of light is proportional to the distance the light travels through the sample.’

## M

Metre (a measure of length – m)

One metre = The distance travelled by light in vacuum in 1/299,792,458 second

Molality

Number of molecules of solute per kilogram of solvent

Molarity

Number of molecules of solute per litre of solution

Mole (1)

‘a cute furry creature that lives in a hole’ or ‘6.022×10^23 molecules of a substance’

Mole (2)

One Mole = The amount of substance containing the same number of atoms/molecules as there are atoms in 12g of Carbon-12

## O

Ohm

‘Unit of Resistance; 1 Ohm = Resistance across two points when one volt applied across the points gives a current flow of 1 ampere.’

Osmolality (two L’s!)

Number of osmoles of solute per kilogram of solvent

Osmolarity (one L!)

Number of osmoles of solute per litre of solution

Osmole

6.022×10^23 osmotically active particles

Osmosis

Movement of a solvent across a semipermeable membrane from a less concentrated solution to a more concentrated solution.

## P

Pascal

One Pascal is defined as one newton acting on one metre square (N/M2)

Perfect Gas

‘A gas which obeys all of the three gas laws completely.’

#### Precision

The ability of a device to reproduce a value (given the same input)

Pressure

Pressure is the amount of force applied to an object per unit surface area.

## R

Relative Humidity

Ratio of water vapour present against the maximum possible (e.g. fully saturated)

Resistor

A resistor is an electrical component which works to reduce current flow by adding resistance to an electrical circuit.

Resonance

Resonance is the ability of an object to oscillate in response to a movement.

## S

Second (a measure of time – s)

One second = 9,192,631,770 oscillations of a Caesium 133 atomic clock.

Siemen

‘Unit of Conductance.’

Specific Heat Capacity

The amount of heat energy required to increase one Kg of a substance by one Degree Centigrade/Kelvin

## T

Temperature

A measurement of the average kinetic energy of a particles in a system.

OR

Propery of an object which determines if heat energy will flow to or from it from another object

Transducer

Transducers are devices which change one type of energy into another type of energy.

Transistor

Transistors are components which open and close to allow movement of electrical current in response to a control voltage.

Transformer

‘A transformer is a device which transfers electrical energy from one circuit to another through electromagnetic induction’

## U

Ultrasound

Ultrasound is sound waves at a frequency above that which is audible to humans.

## V

Volt

‘Unit of Voltage; 1 volt = 1 joule / Coulomb.’

Voltage/Potential Difference

‘Electrical Voltage (aka potential difference) is the energy required to move one coulomb of charge between two points in a circuit.’

## W

Watt

‘Unit of Power; Power (Watts) = Energy (Joules) / Time (Seconds).’

## Z

© Sam Beckett and Physics4FRCA, 2017. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited.