1. Definitions Flashcards
Absolute humidity:
Unit
> The mass of water vapour present in a particular sample of air at a given temperature.
Measured as kg m–3.
Absolute zero:
> The lowest possible temperature where nothing could be colder and all thermal motion stops.
> Precisely 0 K or -273.15 °C.
Ampere (A)
What is it
what is 1 ampere
: SI unit of electric current (SI base unit)
> The current that produces a force of 2 × 10–7 newtons per metre between two parallel wires, of infinite length, 1 m apart in a vacuum.
> The ampere is a measure of the amount of electrical charge passing a given point per unit time.
> An equivalent charge to 6.24 × 1018 electrons (1 coulomb) per second = 1 ampere.
Boiling point:
> The temperature at which
the vapour pressure of a liquid
equals the surrounding ambient pressure
and the liquid changes into a vapour.
Calorie:
> The amount of energy required
to increase the temperature
of 1 g of water by 1 °C.
> 1 calorie = 4.16 J.
> Kcalorie = Abbreviation for kilocalorie which = 1 large calorie (C) or 1000 small calories (c) or 4.16 kJ.
Candela (cd):
The SI unit of luminous intensity (SI base unit).
> 1 cd is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
> A normal candle emits light with a luminous intensity of roughly 1 candela.
Coulomb (C):
unit of
What is it
The unit of charge.
> 1 C is the amount of charge
passing a given point per second,
when 1 A of current is flowing
(see definition of Ampere above).
> 1 C = 1A × 1s.
> 1 C is the magnitude of charge
possessed by 6.24 × 10^18 electrons.
Critical temperature:
> The temperature above which a gas cannot be liquefied by pressure alone.
Freezing point:
> The temperature at which the liquid and solid phases of a substance of specified composition are in equilibrium at a given pressure. > A liquid turns into a solid when its temperature is lowered below its freezing point.
Force:
> That which changes a body’s state of rest or motion.
> Derived SI unit = the newton (N).
> 1N is the force required
to accelerate a 1kg mass
at a rate of 1m per second squared (1N = 1 kg⋅m⋅s–2).
> Force has both magnitude and direction,
making it a vector.
> Force = mass × acceleration (F = ma).
Gas:
> One of the four fundamental states of matter
found between the liquid and plasma phase
(four states = solid, liquid, gas and plasma).
> A substance which is above its critical temperature.
> It is distinguished from liquids and solids by the vast separation between individual gas particles.
> A gas will expand to fill any space available.
Heat capacity:
> The amount of heat required
to raise the temperature of an object by 1 °C
(specific heat capacity × mass of body).
> SI unit of heat capacity = joule per kelvin
Hertz (Hz):
Derived SI unit of frequency
> 1 Hz is 1 cycle per second.
Joule (J):
Derived SI unit of energy
> 1 J is the work done (or energy expended)
to an object when applying of
a force of 1 newton through a distance of 1 m.
> 1 J = 1 N × 1 m or 1 newton metre.
Kelvin (K): SI unit of temperature (SI base unit)
> 1 K is equal to 1/273.16
of the thermodynamic scale temperature
of the triple point of water
> The Kelvin scale is an absolute thermodynamic temperature scale, using absolute zero as its null point.
Kilogram (kg):
SI unit of mass (SI base unit)
> The standard kilogram is the mass of a cylindrical piece of platinum-iridium alloy kept in Sèvres, France.
> The only SI base unit with an SI prefix (Kilo)
> The only SI unit that is still defined by an artifact, and not a fundamental property that can be reproduced in a laboratory.
Kinetic energy:
> The energy a body possesses because of its motion
> It is defined as the energy needed to accelerate the object from a state of rest to its given velocity.
This energy is equal to the work it would do
when decelerating to return to rest.
Latent heat:
> The energy released or absorbed
by a substance when it changes phase
at a given temperature, e.g. ice melting
> The term ‘latent’ describes the ‘hidden’ change
in energy state, as there
is no change in the substance’s
temperature during this phase shift.
Latent heat of fusion (melting):
> The amount of heat required
to convert a unit mass of a solid at its
melting point into a liquid
without an increase in temperature.
Latent heat of vaporisation:
> The amount of heat required to convert
a unit mass of a liquid at its boiling point into vapour without an increase in temperature.
Mass:
> The amount of matter contained in a body
> The SI unit of mass = kilogram
> Unlike weight, mass does not alter under conditions of differing gravity.
Metre (m): SI unit of length (SI base unit)
> Originally defined as the length of a platinum-iridium bar kept near Paris, there were concerns about the bar’s length changing over time.
> Since 1983, defined as the length of the path travelled by light in vacuum
during the time interval of
1/299 792 458 of a second.
Mole:
SI unit of amount of substance (SI base unit)
> Quantity containing the same number of particles
as there are atoms in 12 g of carbon-12.
This number of particles is 6.022 × 1023
and is known as Avogadro’s constant.
Momentum:
> Mass × velocity
Newton (N): Derived SI unit of force
> 1 N is the force required to accelerate
a mass of 1 kg
by 1 m per second squared.
Ohm (Ω):
Derived SI unit of electrical resistance
> 1 ohm is the resistance between two points of a conductor when a constant potential difference of 1 volt applied between them produces a current of 1 ampere.
Pascal (Pa):
Derived SI unit of pressure
> 1 Pa is the force of 1 N acting over 1 m2.
pH:
> The negative logarithm to the base 10 of the hydrogen ion concentration
in a solution.
pH = -log10[H+]
Potential energy:
> The energy of a body or system
as a result of its position in an electric,
magnetic or gravitational field.
It is the potential of that body to do work.
Power:
> The rate of doing work
Unit of power = the watt
1 Watt = 1 joule per second
Pressure:
> Force per unit area
> Derived SI unit is the Pascal (Pa).
Relative humidity:
> The mass of water in a given volume of air, expressed as a percentage
of the maximum mass of water
that the air could hold
at the given temperature.
> The ratio of the water vapour pressure to the saturated vapour pressure.
Resistance:
> Property of a conductor to oppose the flow of current through it
The derived SI unit of electrical resistance is the Ohm (Ω).
Saturated vapour pressure (SVP):
> The pressure exerted by a vapour
when in contact with and in equilibrium
with its liquid phase
within a closed system at a given temperature.
Second (s):
SI unit of time (SI base unit)
> Defined according to the frequency of radiation emitted by caesium-133 in its ground state.
Specific heat capacity (SHC):
> The amount of energy required to raise the temperature of 1 kg of a substance by 1 °C
> SHC of water = 4.16 kJ/kg °C
> SHC of human body = 3.5 kJ/kg °C.
Specific latent heat of vaporisation (boiling
> The amount of heat required to convert a unit mass of a liquid at its boiling point into a gas without an increase in temperature, at a given pressure
Triple point of water:
Define it
what are the measurements
> The temperature and pressure at which
water exists in equilibrium as
liquid water, solid ice and water vapour
> Temperature =
0.01 °C or 273.16 K,
pressure = 0.006 atmosphere or 611.73 pascals.
Vapour:
> A substance in the gas phase below its critical temperature.
Volt (V):
Derived SI unit of electrical potential
> 1 volt is the potential difference
between two points of a conducting wire
when 1 joule of work is don
e to move 1 coulomb of charge between them
> 1 volt is the potential difference between
two points of a conducting wire
when 1 ampere dissipates
1 watt of power between them
> 1 volt will ‘push’ a current
of 1 ampere through a
resistance of 1 Ohm.
Watt (W):
Derived SI unit of power
> 1 watt = 1 joule per second.
Weight:
> The gravitational force acting on an object
> Measured in newtons
> Weight = mass in kg × gravitational acceleration (9.81 ms–2).
A mass of 1 kg will therefore have 9.81 N acting on it on the surface of the earth
(and much less on the surface of the moon).
