Class 12 Physics Practicals - Key Terms & Definitions

Vernier Callipers

A measuring instrument consisting of a main scale with a fixed jaw and a sliding vernier scale with a movable jaw, used to measure internal and external dimensions as well as depth.

Vernier Constant (Least Count)

The smallest value that can be accurately measured with a vernier callipers, calculated using the formula $\text{Least count} = \frac{1}{n} \times \text{main scale division}$, where $n$ vernier scale divisions coincide with $(n - 1)$ main scale divisions.

Zero Correction

The numerical adjustment applied algebraically to an observed scale reading to remove systemic measurement errors, defined as $\text{Zero correction} = -(\text{Zero error})$.

Pitch of a Screw Gauge

The linear distance moved by the screw on the main scale during one complete rotation of the circular scale cap, calculated as $\text{Pitch} = \frac{\text{Distance moved}}{\text{Number of complete rotations}}$.

Screw Gauge Zero Error

The positional discrepancy observed when the zero mark of the circular scale does not coincide with the index line on the main scale while the studs are brought into direct contact.

Back-lash Error

An error in length measurement caused by looseness or wear in the screw threads of a screw gauge, prevented by consistently rotating the screw in only one (forward) direction during observations.

Grayesand's Apparatus

A board setup mounted vertically on rigid legs equipped with frictionless pulleys, weight hangers, and threads, used to measure unknown body weights using vector mechanics.

Law of Parallelogram of Vectors

A vector addition principle stating that if two concurrent forces acting at a point are represented in magnitude and direction by two adjacent sides of a parallelogram, their resultant force is represented in magnitude and direction by the diagonal passing through their intersection point.

Method of Mixtures

A calorimetric principle stating that under thermal equilibrium and zero heat loss to surroundings, heat released by a heated object ($m_b \times S \times (t_3 - t_2)$) equals heat absorbed by cold liquid and calorimeter ($(m_w + m_c \times S_c) \times (t_2 - t_1)$).

Copper Calorimeter Assembly

An insulated apparatus comprising a copper cup, stirrer, thermometer, and outer lagging jacket designed to hold liquids and perform heat exchange measurements with minimal thermal loss.

Resonance Column Tube

An apparatus with a vertical air column over a variable water level used alongside tuning forks to produce standing waves, determine acoustic wavelengths ($\frac{\frac{3\times\frac{1}{\nu}}{4}}{1}$), and compute the speed of sound in air.

Bench Correction

A correction factor applied to raw distances read on an optical bench scale to account for spatial differences between physical optical poles/centers and object/image needle tip locations.

Parallax Error

The relative apparent movement between an object needle image and a pointer tip when an observer's line of sight shifts side-to-side, eliminated when both move in unison without separation.

Graph of $\frac{1}{v}$ versus $\frac{1}{u}$ for Lenses

A straight-line plot with a slope of $-1$ whose axis intercepts yield the inverse focal length ($\frac{1}{f}$) of a spherical lens or mirror.

Ammeter-Voltmeter Method

An experimental technique used to determine electrical resistance by measuring potential difference ($V$) with a voltmeter and current ($I$) with an ammeter, applying Ohm's law ($R = \frac{V}{I}$).

Potentiometer Circuit Setup

An electrical measurement system featuring a long uniform resistance wire, auxiliary power supply, rheostat, galvanometer