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 – B – C – D – E – F – G – H – I – J – K – L – M – N – O – P – Q – R – S – T – U – V – W – X – Y – Z
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.
E
F
Farad
‘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.’
J
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
N
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.
Q
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).’
X
Y
Z
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