Maharashtra HSC Physics key terms

A measure of how strongly a body resists a change in its rotational motion, found by summing each mass element multiplied by the square of its distance from the axis.

The distance from the axis at which the whole mass of a body could be placed so that its moment of inertia stays the same as the actual body.

The rotational analogue of linear momentum, equal to moment of inertia times angular velocity; it stays constant when no external torque acts on a system.

The turning effect of a force about an axis, equal to the product of the force and the perpendicular distance from the axis to its line of action.

Motion in which a round body turns and moves forward together, so the contact point is momentarily at rest and the centre moves at angular speed times radius.

The force per unit length acting along the surface of a liquid, arising because molecules at the surface have higher energy than those inside the bulk.

The upward movement of liquid in a narrow tube caused by surface tension and adhesion, described by height proportional to surface tension and inversely to tube radius.

The angle between the liquid surface and the solid wall inside the liquid at the point of contact; it decides whether a liquid wets a surface.

The pressure difference across a curved liquid surface, larger on the concave side; it is greater for smaller radii and for soap bubbles than for drops.

For steady, non-viscous, incompressible flow along a streamline, the sum of pressure, kinetic energy per unit volume and potential energy per unit volume stays constant.

A device that measures flow rate by narrowing a pipe; the pressure drop in the narrow section is read and related to speed through Bernoulli's principle.

Flow in which every particle passing a given point follows the same path and velocity as earlier particles, so the flow pattern does not change with time.

A dimensionless ratio of inertial forces to viscous forces in a fluid; low values mean smooth laminar flow and high values indicate turbulent flow.

The average distance a gas molecule travels between two successive collisions with other molecules, which depends on molecular size and number density.

The square root of the average of the squared speeds of gas molecules; it rises with temperature and falls as molar mass increases.

The number of independent ways a molecule can store energy, such as translation, rotation or vibration; it fixes the ratio of specific heats for a gas.

The total energy radiated per second by a black body is proportional to the fourth power of its absolute temperature and to its surface area.

The wavelength at which a black body radiates most strongly is inversely proportional to its absolute temperature, so hotter bodies peak at shorter wavelengths.

The heat supplied to a system equals the increase in its internal energy plus the work done by the system, expressing conservation of energy for thermal processes.

A change in which the temperature of the system stays constant, so its internal energy does not change and all heat supplied appears as work done.

A change in which no heat enters or leaves the system, so work done comes at the expense of internal energy and temperature usually falls on expansion.

The greatest possible efficiency of a heat engine working between two temperatures, equal to one minus the lower absolute temperature divided by the higher.

Oscillation in which the restoring force is directly proportional to displacement and directed towards the mean position, giving a sinusoidal variation with time.

The time taken for one complete oscillation, equal to the reciprocal of frequency and, for a spring-mass system, dependent on mass and force constant.

A quantity describing the stage of an oscillation at a given instant, usually written as an angle that fixes the position and direction of motion.

A large amplitude response that occurs when a driving frequency matches the natural frequency of an oscillating system, limited in practice by damping.

A wave pattern formed by two identical waves travelling in opposite directions, with fixed nodes and antinodes and no net transfer of energy.

The lowest frequency at which a stretched string or air column can vibrate, with higher harmonics being whole-number multiples of it for a string.

The periodic rise and fall in loudness heard when two waves of slightly different frequencies superpose, at a rate equal to their frequency difference.

The superposition of two coherent waves giving alternate regions of reinforcement and cancellation; sustained fringes need a constant phase difference.

Two sources that emit waves of the same frequency with a constant phase difference, a requirement for producing a stable interference pattern.

The spreading of light around the edges of an obstacle or through a narrow slit, producing fringes whose width increases with wavelength.

The restriction of light vibrations to one plane, showing that light is a transverse wave; it can be produced by reflection at a suitable angle or by a polaroid.

A vector for a pair of equal and opposite charges, equal to charge times separation, pointing from the negative to the positive charge.

The measure of the electric field passing through a surface, calculated as field strength times area for a flat surface perpendicular to the field.

The total electric flux through any closed surface equals the enclosed charge divided by the permittivity of free space, useful for symmetric charge distributions.

The small average speed with which free electrons move along a conductor under an applied electric field, opposite in direction to the field.

The drift velocity acquired by a charge carrier per unit electric field, indicating how easily carriers move through a material.

A property of a material, equal to resistance times cross-sectional area divided by length, that measures how strongly it opposes current flow.

Two rules for circuits: charge is conserved at a junction, and the sum of potential differences around any closed loop is zero.

A four-resistance network used to measure an unknown resistance; it is balanced when the ratio of two arms equals the ratio of the other two.

The force on a charge moving in a magnetic field, perpendicular to both the velocity and the field, with magnitude proportional to speed and field strength.

A rule giving the magnetic field produced by a small current element; the field falls with the square of distance and depends on the angle to the element.

A particle accelerator in which a magnetic field bends a charged particle into a spiral while an alternating voltage repeatedly boosts its energy.

The production of an electromotive force in a conductor when the magnetic flux linked with it changes, whether by motion or by a changing field.

The induced current always flows in a direction whose magnetic effect opposes the change in flux that produced it, a consequence of energy conservation.

The property of a coil by which a changing current in it induces an opposing emf; it is measured in henry and depends on coil geometry.

A device that changes alternating voltage using two coils on a common core; the voltage ratio equals the ratio of turns in secondary and primary.

The minimum energy needed to remove an electron from the surface of a metal; it depends on the metal and fixes the threshold frequency for photoelectric emission.

The reverse voltage just large enough to stop the fastest photoelectrons, giving their maximum kinetic energy as charge times that voltage.

The wavelength associated with a moving particle, equal to Planck's constant divided by its momentum, so heavier or faster particles have shorter wavelengths.

The radius of the lowest energy orbit of the hydrogen atom in the Bohr model, about 0.053 nanometre, with higher orbits scaling as the square of the number.

A discrete allowed energy that an electron can have in an atom; jumps between levels produce or absorb photons of definite frequency.

The difference between the total mass of the separate nucleons and the mass of the assembled nucleus, appearing as the binding energy of the nucleus.

The energy needed to separate all nucleons in a nucleus completely; per nucleon it peaks near iron and explains energy release in fission and fusion.

The time in which half the nuclei in a radioactive sample decay; after several half-lives the remaining activity becomes very small.

The boundary formed when p-type and n-type semiconductors touch, creating a depletion region and a built-in potential barrier that allows current mainly one way.

The thin zone around a p-n junction where mobile charge carriers have diffused away, leaving fixed ionised atoms and a built-in electric field.

A heavily doped diode designed to work in reverse breakdown at a stable voltage, used to regulate voltage in circuits.

A circuit using diodes that converts alternating current into direct current, either half-wave or full-wave depending on the arrangement.