General Science questions are asked in many competitive examinations across India. The General Science topics that are asked in these examinations are Units and Measurements, Motion, Force and Newton’s Laws of Motion, Work Energy and Power, Gravitation, Atomic Structure, Physical and chemical changes of substances, Cells, Tissues, Genetics etc. We will be giving series of General Science Topics in One liner or short format. Hope, you study well the General Science short notes or one liners given in the post. The topics are given in Parts. You can cover all parts to cover the whole syllabus and you can score really well.

## General Science for Competitive Examinations Part-1

General Science for Competitive Examinations Part-1 consists of: Units and Measurements.

Also Read: Physics- Introduction of Motion

## General Science- Units and Measurements

### Physical Quantities

The quantities that can be **defined **and **measured **are known as physical quantities. They must have numerical **magnitude **and a **unit**. Some examples of Physical quantities are:

- Length
- Force
- Temperature

Physical quantities can be categorised as:

- Fundamental
- Derived
- Supplementary

**Fundamental Quantities **are basic quantities and are independent of each other. Examples of Fundamental quantities are mass, temperature, length, time, current, amount of substance, luminous intensity etc.

**Derived Quantities** are those quantities that are derived from the fundamental quantities. Examples of derived quantities are Momentum (mv), Area (mxm), Volume (lbh), Force, etc.

**Supplementary Quantities **are those quantities that are neither fundamental nor derived. Example of supplementary quantity is plane angle and solid angle.

On the basis of Magnitude and Direction physical quantities are divided into scalar and vector quantities:

**Scalar Quantity**: A physical quantity which has only magnitude and no direction are known as scalar quantity. Distance, Power, Energy, time, speed, volume, density, pressure, work, charge, electric current, temperature, specific heat, frequency, mass etc are scalar quantities.**Vector Quantity:**A physical quantity which has both magnitude and direction is called as a vector quantity. Displacement, Velocity, Torque, Position, acceleration, force, weight, momentum, impulse, electric field, magnetic field, current density, angular velocity, etc are vector quantities.- In exams questions are asked on identifying scalar and vector quantities.

Physical Quantities are measured in Standard Unit and Numerical Value. Standard unit is the unit in which the physical quantity is measured such as metre is a unit of length. Numerical Value is also the magnitude of the quantity. For example if a thread is 15 metres long it means that the unit of the length is metre and length of the thread is 15 times the magnitude of the metre.

## Classification of Units

There are two types in which units are classified:

- Fundamental Units
- Derived Units

Fundamental units are those units that are used to measure the fundamental quantities. The seven fundamental units are Metre (m), Kilogram (Kg), Second (s), Ampere (A), Kelvin (K), Mole (m), and Candela.

**Metre**: One metre is the length of the path travelled by light in vacuum during a time interval of 1/299, 792, 458 of a second.

**Kilogram:** On atomic scale, one kilogram is the mass of 5.0188 1025 × atoms of C 12 isotope.

**Second**: One second is defined as the time interval in which caesium 133 atom completes 9192631770 vibrations in an atomic clock.

**Ampere**: One ampere is defined as the current which, when maintained in two straight infinite length parallel conductor of negligible cross-section and placed 1 m apart in vacuum, would produce a force equal to 2×10 to power -7 Newton per metre of length.

**Kelvin: **One kelvin is the fraction of 1/273.16 temperature of the triple point of water.

**Mole:** One mole is the amount of substance which contains as many elementary entities as there are atoms in 0.012 kg of carbon-12.

**Candela:** One candela is the luminous intensity, in a given direction, of a monochromatic source that emits radiation of frequency 540×10 to power 12 Hz and that has a radiant intensity in that direction of 1/683 W per steradian.

**Derived Units** are those units that are obtained from one or more fundamental units. For example Metre Square, m^{3} , m/sec, km/h etc. As speed is equal to Distance/Time therefore distance unit is metre and time unit is second and hence derived unit of speed is metre/seconds.

**Supplementary units **are units that are used for supplementary quantities. For example Radian and Steradian that are units of Plane angle and solid angle respectively.

**Radian: **One radian is the angle subtended at centre of a circle by an arc equal in length to the radius of the circle.

**Steradian**: One steradian is the solid angle, subtended at the centre of a sphere by that area of the surface of the sphere which is equal to the square of the radius of sphere.

## SI System or International System of Units

The most extensively used unit of measurement in the world is the SI system, also referred to as the international system of units. It is the current version of the metric system.

Under this the common system of measuring physical quantities are:

- CGS System
- FPS System
- MKS System
- SI System

**Fundamental Quantities with their units**

Physical Quantity | Unit | Symbol |

Length | Metre | m |

Mass | kilogram | kg |

Time | second | s |

Electric Current | ampere | A |

Temperature | kelvin | K |

Amount of Substance | mole | mol |

Luminous Intensity | candela | cd |

**Supplementary Quantities with their units**

Plane Angle | radian | rad |

Solid Angle | steradian | sr |

## Physical Quantities Info

Physical Quantity | Formula | SI Unit |

Area | length x breadth | m2 |

Volume | length x breadth x height | m3 |

Density | mass/ volume | Kgm^{–}3 |

Speed or Velocity | distance or displacement/ time | ms^{–}1 |

Linear Momentum | mass x velocity | Kgms^{–}1 |

Acceleration | change in velocity/ time taken | ms^{–}2 |

Force | mass x acceleration | N (Newton) |

Impulse | force x time | Ns |

Pressure | force/ area | Nm^{–}2 |

Work | force x distance | J (Joule) |

Energy | work | J (Joule) |

Moment of Force | force x distance | N-m |

Power | work/ time | W (Watt) |

Surface Tension | force/ length | NM^{–}1 |

Thrust | force | N (Newton) |

Coefficient of Elasticity | stress/ strain | NM^{–}2 |

Moment of Inertia | mass (radius of gyration)square | KG-m2 |

Angular Acceleration | change in angular velocity/ time taken | rad s^{–}2 |

Frequency | number of vibration/ sec | S^{-1} or Hz (Hertz) |

Planck’s Constant | Energy/ Frequency | j-s |

Resistance (R) | Potential difference/ Current | Ω (Ohm) |

Capacitance (C) | charge/ potential difference | F (Farad) |

Specific Resistance or Resistivity | Ra/ l | ohm-m |

Conductance | 1/ R | Ohm^{-1} |

Electric Flux | Electric Field x Area | newton-meters squared per coulomb |

**Astronomical Unit (AU)**: The average distance of the Sun from the Earth is known as one astronomical unit, 1 AU =1.496× 10 to power 11 m.

**Light Year (ly): **The distance that light travels with a velocity of 3×10 to power 8 m/s in one year is known as one light year. 1 light year is equal to 9.461 x 10 to power 15 metres.

**Parsec: **The distance at which average radius of Earth’s orbit around the Sun subtends an angle of 1 arc second is known as one parsec. 1 Parsec =3.08 × 10 to power 16 m = 3.26 light year.

Small Units of Length are Decimetre (10^{-1} metre), Centimetre (10^{-2} metre), Millimetre (10^{-3} metre), Micrometre (10^{-6} metre), Nanometre (10^{-9} metre), Angstrom( 10^{-10}metre), Fermi (10^{-15}metre), Decametre (10 metre), Hectometre (10^{2}metre), Kilometre (10^{3} metre), Megametre (10^{6} metre), Gigametre (10^{9} metre).

1 Inch = | 0.0254 m = | 2.54 cm |

1 Yard = | 3 foot = | 0.9144 m |

1 Foot = | 12 inch = | 0.3048 m |

1 Nautical mile = | 1852 m |

## Units of Mass

1 Quintal (qu) = 100 kg

1 Metric tonne (mt) = 1000 kg

10 Quintal 1 Mega gram (Mg) = 10 to power 3 kg

1 Giga gram (Gg) = 10 to power 6 kg

1 Tera gram (Tg) = 109 kg

1 Slug = 14.57 kg

1 Solar Mass = 1.989 × 1030 kg

1 Chandrashekhar limit = 2.8 × 1030 kg

1 Hectogram (hg) = 10 kg = 100 g

1 Decagram (dag) = 10^{-2} Kg = 10g

1 Gram (g) = 10^{-3} Kg

1 Decigram (dg) = 10^{-4} Kg = 10^{-1} g

1 Centigram (cg) = 10^{-5} Kg

1 Milligram (mg) = 10^{-6} Kg

1 Microgram (µg) = 10^{-9} Kg

1 Nanogram (ng) = 10^{-12} Kg

1 Picogram (pg) = 10^{-15} Kg

1 Atomic mass unit = 1.66 × 10^{-27} Kg

1 Carat = 200 mg

## Prefixes and Symbols

Prefix | Symbol | Power of 10 |

Exa | E | 18 |

Peta | P | 15 |

Tera | T | 12 |

Giga | G | 09 |

Mega | M | 06 |

Kilo | k | 03 |

Hecto | h | 02 |

Deca | da | 1 |

Deci | d | -1 |

Centi | c | -2 |

Milli | m | -3 |

Micro | μ | -06 |

Nano | n | -09 |

Pico | p | -12 |

Femto | f | -15 |

Atto | a | -18 |

## Other Units

1 Minute (min) = 60 seconds

1 Hour (h) = 60 min = 3600 seconds

1 Day (D) = 24 h = 86400 seconds

1 Year (yr) = 365 days = 3.15 x 10^{7} seconds.

1 Century = 100 Years

1 Millisecond (ms) = 10^{-3} seconds

1 Microsecond (µs) =10^{-6} seconds

1 Shake = 10^{-8} seconds

1 Nanosecond (ns) =10^{-9} seconds

1 Picosecond (ps) = 10^{-12} seconds

1 Barn = 10^{-28} m2

1 Hectare = 10^{4} m2

1 litre (L) = 10^{-3} m3

1 Gallon (Gal) = 3.7854 L(US) = 4.546 L (UK)

1 Calorie (cal) = 4.184 Joule

1 Erg = 10^{-7} Joule

1 Kilowatt hour (kWh) = 3.6 x 10^{-6} J

1 Electron volt (eV) = 1.6 x 10^{-19} J

1 Horse power (hp) = 746W

1 Pascal (Pa) = 1 N/m2

1 Bar (bar) = 10^{5} Pa

1 Atmospheric pressure (atm) = 1.01 x 10^{5} Pa.

This ends the Chapter on Units and Measurement. For Part-2, Physics Motion Click Here.