Applied Physics (Term – 1) Units, Dimension and Measurements Vocabulary

Practice flashcards covering units, dimensions, measurement instruments, errors, and significant figures based on the Applied Physics lecture notes.

Unit

The chosen standard of the same kind taken as reference in order to measure a physical quantity.

Physical Quantities

All quantities in terms of which laws of physics can be expressed and which can be measured directly or indirectly, such as distance, speed, time, mass, and force.

Fundamental Units

Units which can neither be derived from one another, nor can they be further resolved into any other units.

Supplementary Physical Quantities

The two additional quantities in the SI system: Plane angle (unit: Radian, symbol: $rad$) and Solid angle (unit: Steradian, symbol: $sr$).

Fundamental SI Units

The seven basic units: Length (Metre), Mass (Kilogram), Time (Second), Temperature (Kelvin), Electric current (Ampere), Luminous intensity (Candela), and Quantity of matter (Mole).

Derived Units

The units of physical quantities which can be expressed in terms of a combination of two or more fundamental units, such as Acceleration ($m s^{-2}$) and Force (Newton).

System of Units

A complete set of units, including both the fundamental units and derived units.

CGS System

A system of units where the fundamental units of length, mass, and time are centimetre, gram, and second respectively.

FPS System

A system of units where the fundamental units of length, mass, and time are foot, pound, and second respectively.

MKS System

A system of units where the fundamental units of length, mass, and time are metre, Kilogram, and second respectively.

SI System

Systeme Internationale d’ Units; a logical system introduced in 1960 by the General conference of weights and measures based on seven fundamental and two supplementary units.

Dimensions

The powers to which the fundamental units have to be raised in order to obtain the units of a physical quantity.

Dimensional Formula for Density

$$\frac{mass}{volume} = \frac{M}{L^3} = [M L^{-3} T^0]$$

Dimensional Formula for Velocity

$$\frac{distance}{time} = \frac{L}{T} = [M^0 L T^{-1}]$$

Dimensional Formula for Force

$$\text{Mass} \times \text{acceleration} = M \times LT^{-2} = [M L T^{-2}]$$

Dimensional Formula for Work

$$\text{Force} \times \text{distance} = MLT^{-2} \times L = [M L^2 T^{-2}]$$

Dimensional Formula for Power

$$\frac{Work done}{time} = \frac{ML^2T^{-2}}{T} = [M L^2 T^{-3}]$$

Principle of Homogeneity

The principle stating that a physical relation must be dimensionally homogeneous, where dimensions of basic units are individually the same in every term on either side of the relation.

Measurements

The quantitative tests of a theory used to test mathematical relations between physical quantities.

Slide Calipers (Or Vernier Calipers)

A measuring instrument used for measuring very short lengths and depths, featuring a main scale and a sliding Vernier scale.

Vernier Constant (VC)

The difference in magnitude between one main scale division (M.S.D.) and one vernier scale division (V.S.D.), also known as the least count ($0.1 \text{ mm}$ or $0.01 \text{ cm}$).

Positive Zero Error (Vernier)

Occurs when the zero of the vernier scale is shifted to the right of the zero of the main scale when both jaws are touching.

Negative Zero Error (Vernier)

Occurs when the zero of the vernier scale is shifted to the left of the zero of the main scale when both jaws are touching.

Pitch (Screw Gauge)

The distance advanced by the screw when it makes one complete rotation, which is the separation between two consecutive threads.

Screw Gauge

An instrument of higher precision than a Vernier Calipers, capable of measuring lengths accurately up to $0.01 \text{ mm}$ or $0.005 \text{ mm}$.

Spherometer

A device used to measure the radius of curvature of a spherical surface, based on the principle of the micrometre screw.

Physical Balance

A device that measures the gravitational mass of an object by comparing it with a standard weight based on the principle of moments.

Principle of Moments

The working principle of a physical balance where equilibrium is reached when weights on two pans are equal because the force arms are equal.

Systematic Error

Errors that tend to be in one direction, either positive or negative, caused by instruments, experimental techniques, or personal factors.

Random Errors

Errors that occur irregularly in sign and size; they can be minimized by taking the arithmetic mean of multiple observations.

Absolute Error

The magnitude of the difference between the true (mean) value of the quantity and the individual measurement value.

Relative Error (\text{\delta a})

The ratio of the mean absolute error to the mean value of the quantity measured: \text{\delta a} = \frac{\Delta a_{mean}}{a_{mean}}

Percentage Error

The relative error expressed as a percentage: $\frac{\Delta a_{mean}}{a_{mean}} \times 100 \text{\%}$

Significant Figures

The number of digits in a result that are known reliably plus the first digit which is uncertain.