BUET Undergraduate Admission Main Written Examination key terms

One of the seven fundamental units from which all other units are built: metre, kilogram, second, ampere, kelvin, mole and candela. Problems often require converting given quantities into these before calculating.

A method of checking or deriving equations by comparing the powers of mass, length and time on each side. It cannot determine dimensionless numerical constants, so it verifies form rather than exact values.

The digits in a measured value that carry real information about precision. Answers to numerical problems should be rounded to match the least precise given data, and trailing zeros matter only when a decimal point is present.

The curved path of an object launched into the air and moving only under gravity, treated as independent horizontal and vertical motions. Range is greatest at a launch angle of 45 degrees when air resistance is ignored.

The velocity of one body as measured from a frame attached to another moving body. It is found by vector subtraction of the two velocities, and is essential for river-boat and rain-man problems.

The turning effect of a force, equal to the product of the force and the perpendicular distance from the pivot to its line of action. It is a vector quantity measured in newton-metres.

A body's resistance to change in its rotational motion, depending on mass and on how that mass is distributed about the axis. It plays the same role in rotation that mass plays in straight-line motion.

The rotational analogue of linear momentum, equal to moment of inertia times angular velocity. It is conserved when no external torque acts, which explains why a spinning skater speeds up on pulling in her arms.

Oscillation in which acceleration is directly proportional to displacement from equilibrium and directed opposite to it. Its period is independent of amplitude, and it describes pendulums and mass-spring systems approximately.

A large increase in oscillation amplitude when a system is driven at a frequency close to its natural frequency. It underlies tuning circuits, musical instruments and some structural failures.

The apparent change in the observed frequency of a wave because source and observer move relative to each other. Approaching motion raises the pitch; receding motion lowers it.

The superposition of two or more coherent waves, producing regions of reinforcement and cancellation. In thin films and Young's double slit it produces the familiar bright and dark fringes.

A plate ruled with many closely spaced parallel slits that disperses light into sharp spectra. Maxima occur where the path difference between adjacent slits equals a whole number of wavelengths.

The emission of electrons from a metal surface when light of sufficiently high frequency falls on it. It shows that light delivers energy in discrete packets called photons.

The minimum energy needed to remove an electron from the surface of a particular metal. It sets the threshold frequency below which no photoelectric emission occurs, however intense the light.

The principle that light and matter show both wave and particle behaviour depending on the experiment performed. Electron diffraction demonstrates the wave nature of particles predicted by de Broglie.

The time in which half the nuclei in a radioactive sample decay. It is constant for a given isotope and independent of the initial amount, temperature and chemical state.

The energy required to separate all nucleons in a nucleus completely. The mass defect of a nucleus, converted through the mass-energy relation, gives its binding energy.

The amount of substance containing as many elementary entities as there are atoms in twelve grams of carbon-12. It links mass in grams to numbers of particles through Avogadro's number.

The number of moles of solute dissolved in one litre of solution. It changes slightly with temperature because solution volume expands, unlike molality, which is based on solvent mass.

The simplest whole-number ratio of atoms of each element in a compound. It is found from percentage composition, while the molecular formula is a whole-number multiple of it.

The reactant that is completely consumed first and therefore fixes the maximum amount of product formed. Identifying it requires comparing the available mole ratio with the balanced equation's stoichiometry.

A solution that resists large changes in pH when small amounts of acid or base are added. It usually contains a weak acid with its conjugate base, or a weak base with its conjugate acid.

When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, it shifts in the direction that opposes the change. It predicts the effect of conditions on yield.

The enthalpy change of a reaction is the same whatever route is taken, provided initial and final states match. It allows unknown enthalpy changes to be calculated from known ones by adding steps.

A measure of how strongly an atom attracts the shared electron pair in a covalent bond. It generally increases across a period and decreases down a group, and it predicts bond polarity.

The mixing of atomic orbitals of similar energy to give an equal number of new, equivalent orbitals suited to bonding. It explains observed molecular shapes such as tetrahedral and trigonal planar geometries.

The existence of compounds with the same molecular formula but different structures or spatial arrangements. Structural isomers differ in connectivity, while stereoisomers differ only in three-dimensional orientation.

The property of a molecule that is not superimposable on its mirror image, usually because a carbon atom carries four different groups. Such molecules rotate plane-polarised light and occur as enantiomers.

An unusually strong intermolecular attraction between a hydrogen atom bonded to nitrogen, oxygen or fluorine and a lone pair on a nearby electronegative atom. It explains water's high boiling point and ice's low density.

The value that a function approaches as its input approaches some point, whether or not the function is defined there. Limits underlie continuity, derivatives and tests for convergence of series.

A function is continuous at a point when its limit there equals the function's value at that point. Graphically it means the curve can be drawn through the point without a break or hole.

A function is differentiable at a point when its derivative exists there, meaning the curve has a well-defined tangent. Differentiability at a point implies continuity there, but the converse fails.

The instantaneous rate at which a function's value changes with respect to its variable, equal to the slope of the tangent. It is defined as the limit of a difference quotient.

The limit of a sum of areas of thin rectangles over an interval, interpreted as signed area under a curve. It is evaluated using an antiderivative through the fundamental theorem of calculus.

A single number associated with a square matrix that indicates whether the matrix is invertible. A zero determinant means the rows are linearly dependent and the system lacks a unique solution.

The matrix which, multiplied by the original square matrix, gives the identity matrix. It exists only when the determinant is non-zero, and it is used to solve linear systems.

Counting methods for arrangements where order matters and selections where it does not, respectively. Permutations suit ordered seating, while combinations suit choosing committees or subsets.

A formula expanding a power of a sum as a series of terms whose coefficients are binomial coefficients. It is used to find particular terms and to approximate expressions for small values.

A number of the form a plus bi, where a and b are real and i squared equals minus one. It has a modulus and argument and can be written in polar form for multiplication and roots.

The rule that a verb must match its subject in number and person. Errors commonly arise with collective nouns, indefinite pronouns and phrases inserted between subject and verb.

A descriptive phrase that does not clearly attach to the word it is meant to describe, producing an unintended or absurd meaning. Rephrasing so the intended noun follows the modifier fixes it.

The use of matching grammatical forms for items in a list or for elements joined by a conjunction. Balanced structure makes writing clearer and is frequently tested in error-correction items.

An expression whose meaning cannot be worked out from the individual words, such as a phrase meaning to postpone. Correct preposition choice within idioms is a common examination point.

A verb combined with an adverb or preposition to produce a new meaning, as in give up or look after. Whether the particle can be separated from the verb depends on the particular expression.

The grammatical feature showing whether the subject performs the action, as in active voice, or receives it, as in passive voice. Passive constructions emphasise the action or its receiver rather than the doer.

The grammatical conversion of direct speech into reported speech, requiring changes in tense, pronouns and time words. The reporting verb and the original tense determine the backshift applied.

পাশাপাশি দুটি ধ্বনির মিলনের ফলে যে পরিবর্তন ঘটে, তাকে সন্ধি বলে। স্বরসন্ধি ও ব্যঞ্জনসন্ধি এর প্রধান দুই ভাগ, এবং সন্ধিবিচ্ছেদ করে মূল শব্দ দেখানো হয়।

একাধিক পদের সংক্ষেপণ করে একটি নতুন পদ গঠনের প্রক্রিয়াকে সমাস বলে। দ্বন্দ্ব, কর্মধারয়, তৎপুরুষ প্রভৃতি এর ভেদ, এবং সমস্যমান পদগুলো ব্যাসবাক্যের মাধ্যমে দেখানো হয়।

বাক্যে ক্রিয়ার সঙ্গে বিশেষ্যের যে সম্পর্ক, তাকে কারক বলে। কর্তা, কর্ম, করণ, সম্প্রদান, অপাদান ও অধিকরণ এই ছয় প্রকার, এবং বিভক্তি সেই সম্পর্ক চিহ্নিত করে।