Test: Unit - SSC CGL MCQ

In scientific terms, a physical quantity is defined as a property of a body, substance, or phenomenon that can be quantified through measurement. This means that physical quantities are attributes that can be observed and measured, such as length, mass, time, temperature, etc. Measurement plays a crucial role in quantifying these physical quantities accurately, aiding in various scientific studies and applications.

The absolute error in a measurement is defined as the difference between the true value and the measured value of a quantity. It represents the discrepancy between the value that was actually measured and the value that is considered to be true or accurate. Absolute error is crucial in assessing the precision and accuracy of measurements in various scientific experiments and applications.

The relative error in measurement is defined as the ratio of the absolute error to the mean value of the quantity being measured. It provides a normalized indication of the error in relation to the average value of the quantity. Relative error is useful in understanding the precision of measurements, especially when comparing different measurements or experiments.

The main systems of units used to measure physical quantities are CGS (Centimetre, Gram, Second), FPS (Foot, Pound, Second), MKS (Metre, Kilogram, Second), and SI (International System of Units). The International System of Units (SI) is the most widely used system for scientific and technical purposes globally. It provides a coherent set of units for measurements in areas such as length, mass, time, electric current, temperature, and many other physical quantities.

The MKS system stands for Metre, Kilogram, Second, where length is measured in meters, mass in kilograms, and time in seconds. This system is commonly used in scientific and engineering applications due to its simplicity and coherence, making it easier to work with various physical quantities in calculations and experiments.
the SI (International System of Units) also includes these units (meters, kilograms, seconds) and is the modern, widely accepted system used in most scientific and technical fields.

The CGS system, which stands for Centimetre, Gram, Second, utilizes centimeters for length, grams for mass, and seconds for time. While not as commonly used in modern scientific contexts, the CGS system finds applications in specific fields like astronomy and particle physics due to its convenience for certain calculations and measurements.

The Radian (rad) in the SI system is a unit of plane angle. This unit is crucial for measuring angles in a variety of fields such as mathematics, physics, and engineering. One radian is defined as the angle subtended at the center of a circle by an arc equal in length to the circle's radius. Understanding this unit is essential for calculations involving rotational motion, oscillations, and trigonometry.

The Steradian (sr) in the SI system is the unit of solid angle. This fundamental quantity is vital for measuring how a three-dimensional object appears from a particular point in space. Understanding the Steradian is crucial in fields such as optics, astronomy, and computer graphics where the measurement of angles in 3D space is essential for accurate calculations and simulations.

In the SI system, there are two supplementary fundamental units: the Radian (rad) for plane angle and the Steradian (sr) for solid angle. These units supplement the seven base fundamental quantities to provide a comprehensive framework for measuring various physical quantities accurately. Understanding these supplementary units is essential for precise calculations and measurements in fields that require angular considerations.

The SI unit of mass, is the kilogram (kg). It is defined as the mass of 5.0188 × 10²⁵ atoms of carbon-12. The kilogram is a fundamental unit in the International System of Units and is used as a standard for mass measurements worldwide.

The unit of length defined as the distance light travels in a vacuum in 1/299,792,458 of a second is the metre (m). This unit is fundamental in the International System of Units (SI) and serves as the basis for measuring length in the metric system.

The SI unit of time, defined as 1/86,400 of a mean solar day, is the second. This standard unit of time is crucial in various fields such as physics, engineering, and everyday timekeeping. It provides a consistent measure for timing and synchronization across different contexts.

The percentage error in measurement is calculated by multiplying the relative error by 100. This calculation helps express the error as a percentage of the measured value, providing a clear understanding of the magnitude of error relative to the size of the quantity being measured. Percentage error is valuable in assessing the accuracy of measurements and determining the reliability of experimental results.

The FPS system, which stands for Foot, Pound, Second, incorporates feet for length, pounds for mass, and seconds for time. This system was historically used in the United States and the United Kingdom but has largely been replaced by the more standardized International System of Units (SI) in scientific and technical fields worldwide.

The most widely accepted system for fundamental quantities, adopted in 1971, is the International System of Units (SI). This system provides a standardized framework for measuring physical quantities, ensuring consistency and accuracy in scientific and engineering applications worldwide. Adherence to the SI system is crucial for promoting international cooperation and understanding in the realm of measurement and scientific research.