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# SI UNITS OF SOME PHYSICAL QUANTITIES

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## SI UNITS OF SOME PHYSICAL QUANTITIES

Units are defined as those tools using which we can measure any physical quantities effectively. For example, if we want to measure length then that can be measured in meters, centimeters, feet etc, again if we have to measure mass then that can be measured in kilograms, grams etc.

So from the above example we can say that there are many units which can be used to measure a particular quantity.

#### International System of Units ( SI units )

The standardized system of measurement that is most well known and used in the world is the ” International System of Units”. It is NOT abbreviated as “ISOU”. Instead , the ” International System of Units” is abbreviated as ” SI Units” .

The letters SI were taken from the French words that mean International System of Units ( it seems that historically the French were very involved with standardization).

The SI system has “seven base” quantities. These are considered as basic quantities from which other quantities can be mathematically derived. The seven base quantities are:

#### Advantages of SI System of Unit

1. It is a coherent system of unit.
2. It is a rational system of unit.
3. SI is a metric system.

#### SI UNITS OF SOME PHYSICAL QUANTITIES USED:

Acceleration,​​ a​​ is metre per second squared​​ (m/s2)

Acceleration due to​​ gravity,​​ g​​ is m/s2​​ (or​​ N/kg)

Activity (of a radio nuclide) is Becquerel​​ (Bq)

Amount of substance is Mole​​ (mol)

Area​​ (A) is square meter (m2)

Capacitance is Farad​​ (F)​​ [other =​​ C/V]

TOPIC 3: MAGNETISM | PHYSICS FORM 2

Density is kilogram per cubic meter (kg/m3) (or​​ g/cm3)

Effort, E and​​ Load,​​ L in machine is​​ Newton​​ (N)

Electric Charge, Quantity of electricity is Coulomb​​ (C)

Electric current, I is Ampere​​ (A)

Electric Resistance is Ohm () [other=​​ V/A]

Electric Potential difference, Emf is Volts (V) [other​​ =W/A]

Energy, Work,​​ Quantity of heat is​​ Joule​​ (J)

Extension ,​​ e​​ is meter​​ (m)

Force (Weight)/Tension is​​ Newton​​ (N)​​ [others =​​ kgm/s2]

Frequency , F is Hertz​​ (Hz)

Heat Capacity is Joule per Kelvin​​ (J/K)

Impulse,​​ J​​ is​​ Newton​​ second​​ (Ns)

Length,​​ (L),​​ Displacement and distance is meter​​ (m)

Linear​​ expansivity,​​ ∝​​ is per Kelvin (K-1​​ ) [ per Celsius,​​ C-1]

Mass is kilogram (kg) [others = grams,​​ tones]

Moment of force (M) is​​ Newton​​ meter​​ (Nm)

Momentum,​​ p​​ is kilogram meter per second​​ (kgm/s)

Power​​ is Watts​​ (W)​​ [others = Horsepower,​​ Hp]

Pressure, stress is Pascal (Pa) [others = N/m2, mmHg, Bar,​​ Atm]

Resistivity,​​ 𝜌​​ is Ohm meter​​ (m)

Specific latent heat of vaporization/fusion is Joule per kilogram​​ (J/kg)

Specific heat Capacity, C is Joule per kilogram Kelvin​​ (J/kgK)

Speed, Velocity is meter per second​​ (m/s)​​ [other =​​ km/h]

Spring constant, k​​ (Force​​ constant) is Newton per meter​​ (N/m)

Temperature is Kelvin​​ (K)​​ [others = Celsius,​​ C/ Fahrenheit,​​ F]

Time is​​ second​​ (s)[others = minutes, hours]

Volume is cubic meter (m3)​​ [others =​​ cm3,mm3]

Wave​​ length,​​ ​​ is Meter​​ (m)​​

#### UNITS CONVERSION

​​​​ 1​​ kilo​​ unit = 1000 (103)​​ Units

EUROPEAN NATIONALISM : THE RISE OF GERMANY , ITALY AND ITS IMPACT

​​​​ 1​​ Mega​​ units = 1,000,0000 (106)​​ units

​​​​ 1​​ Giga​​ unit = 1,000,000,000 (109)​​ units

​​ 1Unit = 0.001 (10-3) mill​​ unit

​​ 1​​ Unit= 0.000001(10-6) micro​​ unit

​​ 1​​ unit = 0.000000001 (10-9) nano​​ unit

​​ 10m/s =​​ 36km/h

​​​​ 1​​ m3​​ = 1000​​ Litres

​​ 1 Litre = 1000 cm3

​​ 1g/cm3​​ = 1000kg/m3

​​ 1 atm = 760 mmHg = 1.01325 x 105​​ Pa​​ (N/m2)

​​ 1 Hp = 746W

​​ 1AU​​ = 1.4960 x 1011m​​ →​​ AU​​ = Astronomical​​ unit

#### Symbols:

Mega =​​ M, Kilo​​ =​​ k,​​ Giga​​ =​​ G, mill =​​ m,​​ micro =𝝁, nano =​​ n

Examples:

Change the​​ following

3MHz into Hz​​ →​​ 1MHz = 106Hz, 3MHz =Hz?, = 3×106Hz

(b) 5k​​ into​​ →​​ 1k​​ = 103, 5k​​ =?​​ , 5k​​ =​​ 5000

50mA​​ into​​ A→​​ 5​​ x​​ 10-2A or​​ 0.05A

8​​ 𝜇F​​ into​​ F→​​ 8 x 10-6​​ F

50 kg​​ into​​ g​​ 50,000g

25m/s into km/h​​ ​​ 90k/h