Physical Quantities and units Flashcards
What is a physical quantity?
Physical quantities are those which can be measured, for example: length, mass, weight, speed, force, momentum, time etc. Every physical quantities has a numerical value and a unit.
What are base quantities?
Base Quantities are those quantities which require only one measurement. They are seven in number.
How many base Quantities are there?
The seven base quantities are:
Length-meter-m
Mass-Kilogram-Kg
Time-Second-S
Electrical current-Ampere-A
Temperature-Kelvin-K
Amount of Substance-Mole-mol
Luminous Intensity-Candela-cd
What are base units?
The units of the base quantities are known as base units.
What are derived quantities?
Physical quantities other than base quantities are called derived quantities, as they require more than one measurement.
What are derived units?
They can be derived from the relationship between the derived quantities and the base quantities.
What are the derived Quantities?
Area
Volume
Density
Velocity
Acceleration
Force
Energy/work
Kinetic Energy
Potential Energy
Power
Pressure
Charge
Frequency
Momentum
Electrical resistance
Voltage
Strain
Spring Constant
Potential Difference
What is the formula and derived units for area?
LxL=pier^2
Derived units=mxm=m^2
What is the formula and derived units for volume?
LxLxL=m^3
Derived units=m^3
What is the formula and derived units for density?
mass/volume
Derived Units:
mass=kg
volume=m3
hence density=kg m-3
What is the formula and derived units for velocity?
velocity=distance/time
Derived Units:
distance: m
time: s
hence velocity= m s-1
What is the formula and derived units for acceleration?
acceleration: a = Δv/Δt
Derived Units:
Velocity: m s-1
time: s
hence acceleration= m s-2
What is the formula and derived units for force?
Force: mass x acceleration
Derived Units:
mass=kg
acceleration= m s-2
hence force= kg m s-2
What is the formula and derived units for energy/word?
Energy/work: force x distance
Derived units:
force: kg m s-2
distance: m
Hence energy/work: kg m^2 s-2
What is the formula for kinetic energy?
1/2 mv^2
where m=mass
v=velocity
What is the formula for potential energy?
mgh
where m= mass
g=acceleration due to gravity=9.8 m s-2
h=height
What is the formula and derived units for power?
power=energy/time
energy=kg m^2 s-2
time: s
hence power=kg m^2 s-3
What is the formula and derived units for pressure?
pressure=force/area
force=kg ms-2
area=m^2
hence pressure: kg m-1 s-2
What is the formula and derived units for charge?
charge: current x time
current= A
Time= s
hence charge= As
What is the formula and derived units for frequency?
frequency=1/t
time=s
hence frequency=s-1
What is the formula and derived units for electrical resistance?
electrical resistance= voltage/current
voltage: kg m2 s-3 A-1
current: A
hence electrical resistance: kg m2 s-3 A-2
What is the formula and derived units for momentum?
momentum= mass x velocity
mass=kg
velocity=ms-1
What is the formula and derived unit for voltage?
voltage= current x resistance
current= A
charge=As
hence voltage= A^2 s
(check)
What is the formula and derived unit for specific heat capacity?
Specific heat capacity=
What is the formula and derived unit for strain?
Strain=extension/length
extension=m
length=m
hence strain has no units.
What is the formula and derived unit for young modulus?
Young Modulus=Stress/Strain
Stress= Kg m-1 s-2
strain=no units
Hence Young Modulus: Kg m-1 s-2
What is the formula and derived units of spring constant?
What is the formula and derived units of potential difference?
Potential difference= energy/charge
Energy=kg m^2 s-2
Charge=As
Hence potential difference= kg m^2 s-3
What are prefixes?
Prefixes are multiples or submultiples of the base units.
What are the four multiples?
Kilo- 10^3-K
Mega-10^6-M
Giga-10^9-G
Tera-10^12-T
What are the four submultiples?
Milli-10^-3-m
Micro-10^-6- µ
Nano-10^-9-n
Pico-10^-12-p
What is meant by homogeneity of equation?
An equation is said to be homogenous if the base units of every term in the equation are identical.
What is the volume of a cylinder?
Volume of a cylinder: πr2h
