Brief Summary
This YouTube video by WebSankul Official provides a comprehensive overview of physics questions previously asked in various competitive exams. It focuses on fundamental physical quantities, their units, and conversions between different units. The lecture covers topics such as SI units, derived units, scalar and vector quantities, and practical units for measuring length, mass, time, and other physical properties.
- Covers questions from various competitive exams.
- Focuses on fundamental physical quantities and their units.
- Includes unit conversions and definitions.
Introduction
The video starts with a welcome message and an introduction to the WebSankul Official YouTube channel. The presenter mentions that they will be continuing their series on previously asked science questions, focusing on basic physics concepts relevant to various exams. The presenter encourages viewers to like and share the video, acknowledging the effort put into creating the content.
Fundamental and Derived Quantities
The lecture begins with a question about identifying fundamental quantities. It explains that the SI system has seven fundamental quantities: mass (kilogram), time (second), length (metre), electric current (ampere), temperature (kelvin), amount of substance (mole), and luminous intensity (candela). Density, being a derived quantity (mass/volume), is not a fundamental quantity.
Prefixes and Conversions
This section covers prefixes used in the metric system, such as centi (10^-2), deci (10^-1), deca (10^1), hecto (10^2), and kilo (10^3). An example question involves arranging these prefixes in ascending order. The presenter emphasises the importance of knowing these prefixes for solving numerical problems.
Scalar and Vector Quantities
The discussion moves to scalar and vector quantities, explaining that vector quantities have both magnitude and direction. Displacement is given as an example of a vector quantity, while path length, speed, and temperature are scalar quantities. Other vector quantities mentioned include momentum, force, and impulse.
FPS System and Unit Systems
The video explains the FPS (foot, pound, second) system used by the British and compares it to the CGS (centimetre, gram, second) system used by the French. It also introduces the MKS (metre, kilogram, second) and MKS A (metre, kilogram, second, ampere) systems.
Units of Measurement
This part addresses a question about units used for measuring distance, clarifying that a milestone is not a standard unit of distance measurement. Other units like micron, millimetre, and light-year are used for measuring small, medium, and large distances, respectively.
SI Units and Applications
The presenter revisits SI units, matching length with metre, electric current with ampere, temperature with kelvin, and luminous intensity with candela. The importance of understanding these fundamental units for various applications is highlighted.
Practical Units and Conversions
The lecture covers practical units like Fermi for measuring the size of an atom (10^-15 metres) and the use of atomic clocks for measuring small time intervals. It also discusses the Kelvin scale for temperature measurement.
Pressure and Weight Measurement
The video explains that pressure is measured in pascals (newtons per square metre) and weight is measured using a spring balance. The SI unit of weight is the newton.
Mass and Standard Units
Mass is measured using a balance, and its SI unit is the kilogram. The presenter asks the audience to specify how many kilograms are in one tonne (1000 kg).
Power and Energy Units
Power is defined as the rate of doing work, measured in watts (joules per second). The presenter also mentions horsepower, asking the audience to specify how many watts are in one horsepower (746 watts). Energy is measured in joules.
Astronomical Units
The video introduces the astronomical unit (AU) as the average distance between the Earth and the Sun. It also covers the light-year as a unit of distance, asking the audience how many astronomical units are in one light-year (63,000 AU).
Light Year and Kilometre Conversion
The presenter explains the relationship between a light-year and kilometres, stating that one light-year is approximately 9.46 x 10^12 kilometres. The audience is then asked to calculate how many kilometres are in 10 light-years (9.46 x 10^13 kilometres).
Controversial Questions and Nautical Miles
This section discusses a controversial question about measuring distances between planets, where the official answer key accepted both kilometres and miles. The presenter then moves on to nautical miles, explaining that one nautical mile is approximately 1.852 kilometres or 1852 metres.
Nanometres and Hectares
The video covers nanometres, stating that one nanometre is 10^-9 metres. The presenter then discusses hectares and Ares, explaining that one hectare is equal to 100 Ares.
Centimetres and Metres
The presenter revisits the relationship between centimetres and metres, stating that 100 centimetres is equal to 1 metre.
Advanced Unit Conversions
This section includes a more complex unit conversion, asking how many nanometres are in one metre (10^9 nanometres).
Cubic Metres and Kilolitres
The presenter explains that one cubic metre is equal to 1 kilolitre.
Angstroms and Litres
The video covers Angstroms, stating that one Angstrom is 10^-10 metres. It also asks how many centimetres are in one Angstrom (10^-8 centimetres). The presenter then revisits litres, stating that one kilolitre is equal to 1000 litres.
Tonne and Inches
The presenter reiterates that one tonne is equal to 1000 kilograms. The video then covers the conversion between metres and inches, stating that one metre is approximately 39.37 inches.
Terabytes and Fathoms
The video explains that one terabyte (TB) is equal to 1024 gigabytes (GB). Finally, the presenter discusses fathoms, stating that one fathom is equal to 6 feet and is used to measure the depth of the sea.
Conclusion
The video concludes with a summary of the topics covered and encouragement for viewers to continue their studies. The presenter also promotes various courses available on the WebSankul application, including courses for Talati and Constable exams.
