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**Chapter 1. Rotational dynamics**

(1) Uniform circular motion.

Ans. A particle is said to perform uniform circular motion if it moves in a circle or a circular are at constant linear speed or constant angular velocity.

(2) Centripetal force.

Ans. In the uniform circular motion of a particle, the centripetal forces and produces the centripetal acceleration necessary to make the particle is the force on the particle which at every instant points radially inward move in its circular path.

(3) Centrifugal force.

Ans. In the reference frame of a particle performing circular motion,centrifugal force is defined as a fletitions, radially outward force on the particle and is equal in magnitude to the particle's mass times the centripetal acceleration of the reference frame, as measured from an inertial frame of reference.

(4) Angle of banking.

Ans. Angle of banking is the angle of inclination of a banked road

(5) Conical pendulum.

Ans. A conical pendulum is a simple pendulum whose bob revolves in with the horizontal.a horizontal circle with constant speed such that the string describes the surface of a right circular cone.

(6) Moment of inertia.

Ans. The moment of inertia of a body about a given axis of rotation is defined as the sum of the products of the masses of the particles of the body and the squares of their respective distances from the axis of rotation

(7) Radius of gyration.

Ans. The radius of gyration of a body rotating about an axis is defined as the distance between the axis of rotation and the point at which the entire mass of the body can be supposed to be concentrated so as to give the same moment of inertia as that of the body about the given axis.

(8) Angular momentum of a particle.

Ans. The angular momentum of a particle is defined as the moment of the linear momentum of the particle. If a particle of mass m has linear momentum p (=mo), then the angular momentum of this particle with respect to a point is a vector quantity defined as 7 = xp=m(xv). wherer is the position vector of the particle with respect to O.

**Chapter 2. Mechanical properties of fluids **

(9) Gauge pressure.

Ans. Gauge pressure is the pressure exerted by a fluid relative to the local atmospheric pressure. Gauge pressure, P.-P-P.where p is the absolute pressure and p, is the local atmospheric pressure.

(10) Absolute pressure.

Ans. The absolute pressure, or total pressure, is measured relative to absolute zero on the pressure scale-which is a perfect vacuum-and is the sum of gauge pressure and atmospheric pressure. It is the same as the thermodynamic pressure,

(11) Range of molecular attraction or molecular range.

Ans. Range of molecular attraction is defined as the maximum distance between two molecules up to which the intermolecular force of attraction is appreciable.

(12) Sphere of influence.

Ans. The sphere of influence of a molecule is defined as an imaginary sphere drawn with the molecule as the centre and radius equal to the range of molecular attraction.

(13) Surface tension.

Ans. Surface tension of a liquid is defined as the tangential force per & unit length, acting at right angles on either side of an imaginary line drawn on the free surface of the liquid.

(14) Surface energy.

Ans. Surface energy is defined as the extra (i.e., increased) potential energy of a liquid surface with an isothermal increase in the surface area

. (15) Angle of contact.

Ans. The angle of contact for a liquid-solid pair (a liquid in contact with a solid) is defined as the angle between the surface of the solid and the tangent drawn to the free surface of the liquid at the extreme edge of the liquid, as measured through the liquid.

(16) Velocity gradient in a steady flow.

Ans. In a steady flow of a fluid past a solid surface, the rate at which the velocity changes with distance within a limiting distance from the surface is called the velocity gradient.

(17) Coefficient of viscosity.

Ans. The coefficient of viscosity of a fluid is defined as the viscous drag per unit area acting on a fluid layer per unit velocity gradient established in a steady flow.

**Chapter 3. Kinetic theory of gases and Radiation**

(18) Root mean square speed of gas molecules.

Ans. Root mean square speed of gas molecules is defined as the square root of the arithmetic mean of the squares of the speeds of all molecules of the gas at a given temperature.

(19) Molar heat capacity of a gas at constant volume.

Ans. Molar heat capacity of a gas at constant volume is defined as the quantity of heat required to raise the temperature of one mole of the gas through one degree (1 °C or 1 K), when its volume is kept constant.

(20) Molar heat capacity of a gas at constant pressure.

Ans. Molar heat capacity of a gas at constant pressure is defined as the quantity of heat required to raise the temperature of one mole of the gas through one degree (1 °C or 1 K), when its pressure is kept constant.

(21) Coefficient of absorption (Absorptance).

Ans. The coefficient of absorption (absorptance or absorptive power) of a body is defined as the ratio of the quantity of radiant energy absorbed by the body to the quantity of radiant energy incident on the body in the same time,

(22) Coefficient of reflection (Reflectance).

Ans. The coefficient of reflection (reflectance) of the surface of a body is defined as the ratio of the quantity of radiant energy reflected by the surface to the quantity of radiant energy incident on the surface in the same time.

(23) Coefficient of transmission (Transmittance).

Ans. The coefficient of transmission (transmittance) of a body is

defined as the ratio of the quantity of radiant energy transmitted by the body to the quantity of radiant energy incident on the body in the same time.

(24) Emissive power of a body.

Ans. Emissive power of a body at a given temperature is defined as the quantity of radiant energy emitted by the body per unit time per unit surface area of the body at that temperature.

(25) Coefficient of emission (emissivity) of a body.

Ans. Coefficient of emission (emissivity) of a body is defined as the ratio of the emissive power of the body to the emissive power of a blackbody at the same temperature as that of the body.

**Chapter 4. Thermodynamics**

Ans. Internal energy of a system is defined as the sum of the kinetic energies of the atoms and molecules belonging to the system, and the potential energies associated with the interactions between these constituents (atoms and molecules).

(27) Efficiency of a heat engine.

Ans. The efficiency of a heat engine is defined as the ratio of the work output to the corresponding heat input, both work and heat expressed in the same unit. OR W The thermal efficiency of a heat engine is defined as Q

(28) Coefficient of performance of a refrigerator.

Ans. The coefficient of performance or quality factor or Q-value of a refrigerator is defined as the ratio of the heat absorbed by the working substance or refrigerant from the cold reservoir (output) to the corresponding work done on the working substance (input). KW QcI-IQ:

**Chapter 5. Oscillations **

(29) Periodic motion.

Ans. A motion that repeats itself at definite intervals of time is said to be a periodic motion.

(30) Oscillatory motion,

Ans. A periodic motion in which a body moves back and forth over the same path, straight or curved, between alternate extremes is said to be an oscillatory motion.

(31) Linear simple harmonic motion.

Ans. Linear simple harmonic motion is defined as the linear periodic motion of a body in which the force on the body (or its acceleration) is always directed towards the mean position of the body and its magnitude is proportional to the displacement of the body from the mean position. OR A particle is said to perform linear simple harmonic motion (SHM) if it oscillates about a point of stable equilibrium, subject to a force alway, directed towards that point and whose magnitude is proportional to the displacement of the particle from that point.

(32) Period or periodic time of SHM.

Ans. The time taken by a particle performing simple harmonic motion to complete one oscillation is called the period or periodic time of SHM.

(33) Frequency of SHM

Ans. The number of oscillations performed per unit time by a particle executing SHM is called the frequency of SHM.

(34) Amplitude of SHM.

Ans. The magnitude of the maximum displacement of a particle performing SHM from its mean position is called the amplitude of SHM.

(35) Phase of SHM.

Ans. Phase of simple harmonic motion represents the state of oscillation of the particle performing simple harmonic motion (SHM), i.e., it gives the displacement of the particle and its direction of motion from the equilibrium position.

The displacement of a particle in SHM is given by x = A sin (ost + o). The angle (ost + x) is called the phase angle or simply the phase of SHM.

(36) Ideal simple pendulum.

Ans. An ideal simple pendulum is a heavy point mass suspended from a rigid support by a weightless, inextensible and twistless string, and set oscillating under gravity through a small angle in a vertical plane.

(37) Seconds pendulum,

Ans. A simple pendulum of period two seconds is called a seconds pendulum.

(38) Angular SHM

Ans. Angular SHM is defined as the oscillatory motion of a body in which the restoring torque responsible for angular acceleration is directly proportional to the angular displacement and its direction is opposite to that of angular displacement.

**Chapter 6. Superposition of waves**

(39) Progressive wave OR Travelling wave.

Ans. A progressive wave or a wave motion is a periodic or oscillatory disturbance in a medium or in vacuum which is propagated without any damping and obstruction from one place to another at a finite speed.

(40) Transverse progressive wave.

Ans. A progressive wave in which the vibration of the individual particles of the medium is perpendicular to the direction of propagation of the wave is called a transverse progressive wave.

(42) Stationary wave OR Standing wave.

Ans. When two identical progressive waves, i.e., waves having the same amplitude, wavelength and speed, propagate in opposite directions through the same region of a medium, their superposition under certain conditions creates a stationary interference pattern called a stationary wave or a standing wave.

(43) Transverse stationary wave.

Ans. When two identical transverse progressive waves travelling in opposite directions along the same line superimpose, the resultant wave produced is called a transverse stationary wave.

(44) Longitudinal stationary wave.

Ans. When two identical longitudinal progressive waves travelling in opposite directions along the same line superimpose, the resultant wave produced is called a longitudinal stationary wave.

(45) Free vibrations.

Ans. Vibrations of a body, free to vibrate when it is disturbed from its equilibrium position and left to itself are called free vibrations.

(46) Forced vibrations.

Ans. The vibrations of a body in response to an external periodic force are called forced vibrations,

(47) Resonance.

Ans. If a body is made to vibrate by an external periodic force, whose frequency is equal to the natural frequency (or nearly so) of the body, the body vibrates with maximum amplitude. This phenomenon is called resonance.

(48) Beats.

Ans. A periodic variation in loudness (or intensity) when two sound notes of slightly different frequencies are sounded at the same time is called beats.

(49) Period of beats.

Ans. The time interval between successive maxima or minima of sound at a given place is called the period of beats.

(50) Beat frequency.

Ans. The number of beats produced per unit time is called the beat frequency

**Chapter 7. Wave optics**

(51) Wavefront.

Ans. A wavefront is defined as a surface of all neighbouring points which receive light waves from a source at the same instant and are in the same phase.

(52) Wave normal.

Ans. A wave normal at a point on a wavefront is defined as a line drawn perpendicular to the wavefront in the direction of propagation of the wavefront

(53) The Brewster angle OR the polarizing angle.

Ans. The Brewster angle or the polarizing angle for an interface is the angle of incidence for a ray of unpolarized light at which the reflected ray is completely plane polarized.

(54) Interference of light.

Ans. Interference of light is the phenomenon in which the superposition of two or more light waves produces a resultant disturbance of redistributed light intensity or energy.

(55) Diffraction of light.

Ans. Diffraction of light is the phenomenon of bending of light waves at an edge into the region of the geometrical shadow.

(56) Resolving power of an optical instrument.

Ans. The resolving power of an optical instrument is defined as the reciprocal of its limit of resolution which is the smallest linear or angular separation between two point objects which appear just resolved when viewed through the instrument.

(57) Resolving power of a microscope.

Ans. The resolving power of a microscope is defined as the reciprocal of the least separation between two closely spaced points on an object which are just resolved when viewed through the microscope.

**Chapter 8. Electrostaties**

(59) Electric potential difference.

Ans. The electric potential difference between two points in an electric field is defined as the work done per unit charge by an external agent against the electric force in moving an infinitesimal positive charge from one point to the other without acceleration.

(60) Electric potential.

Ans. The electric potential at a point in an electric field is defined as the work per unit charge that must be done by an external agent against the electric force to move without acceleration a sufficiently small positive test charge from infinity to the point of interest.

(61) The electronvolt.

Ans. The electronvolt (symbol, eV) is the increase in the kinetic energy of a particle with a charge equal in magnitude to the elementary charge e when the particle is accelerated through a potential difference of one volt.

(62) Electric potential gradient.

Ans. The rate of change of electric potential with distance in a specified direction is called the electric potential gradient in that direction.

(63) Electric polarization.

Ans. The electric polarization at every point within a dielectric is defined as the electric dipole moment per unit volume. It has the direction of the external electric field.

(64) Capacitance of a capacitor.

Ans. The capacitance of a capacitor is defined as the ratio of the charge on either conductor to the potential difference between the two conductors forming the capacitor

(65) The SI unit of capacitance or capacity.

OR The farad. Ans. The SI unit of capacitance is the farad. The capacitance of a capacitor is said to be one farad if a charge of one coulomb is required to increase the potential difference between the two conductors forming the capacitor by one volt. (1 farad = 1 coulomb/volt) OR

the capacitance of an isolated conductor is said to be one farad if a charge of one coulomb is required to increase its potential by one volt.

**Chapter 10. Magnetic fields due to electric current**

(66) The ampere.

Ans. The ampere that constant current which if maintained in two infinitely long straight parallel wires, placed one metre apart in vacuum, would cause each conductor (wire) to experience a force per unit length of 2 x 10-newton per metre.

**Chapter 11. Magnetie materials**

(67) Magnetization.

Ans. The magnetization of the material is defined as the net magnetic moment per unit volume of a material.

(68) Magnetic intensity.

Ans. The magnetic intensity is defined as the magnetic induction in an isotropic medium divided by the permeability of the medium.

**Chapter 12. Electromagnetic induction **

(69) Magnetic flux.

Ans. The magnetic flux through a given area in a magnetic field is defined as the total number of magnetic lines of force passing normally through that area.

(70) Electromagnetic induction.

Ans. Electromagnetic induction is the phenomenon of production of emf in a conductor or circuit due to the motion of the conductor in a magnetic field or by a changing magnetic flux through the circuit.

(71) Self induction,

Ans. The phenomenon of production of induced emf in a coil, due to the change of current in the same coil, is called self induction.

(72) Self inductance OR Coefficient of self induction.

Ans. The self inductance or the coefficient of self induction of a coil is defined as the emf induced in the coil per unit time rate of change of current in the same coil. OR (using L=N/I), the self inductance of a coil is the ratio of magnetic flux linked with the coil to the current in it.

(73) The henry.

Ans. The self-inductance of a coil is 1 henry if an emf of 1 volt is induced in the coil when the current through the same coil changes at the rate of 1 ampere per second, OR

The mutual inductance of a coil (secondary) with respect to a magnetically linked neighbouring coil (primary) is one henry if an emf of 1 volt is induced in the secondary coil when the current in the primary coil changes at the rate of 1 ampere per second.

(74) Mutual induction,

Ans. The phenomenon of production of induced emf in one coil due to changing current in a magnetically linked neighbouring coil is called mutual induction.

(75) Mutual inductance OR Coefficient of mutual induction. BB

Ans. The mutual inductance or the coefficient of mutual induction of two magnetically linked coils is equal to the flux linkage of one coil per unit current in the neighbouring coil. OR

The mutual inductance or the coefficient of mutual induction of two magnetically linked coils is numerically equal to the emf induced in one coil (secondary) per unit time rate of change of current in the neighbouring coil (primary).

**Chapter 13. AC circuits**

(76) Average value of an alternating emf or current.

Ans. The average or mean value of an alternating emf/current is defined as its average value over half cycle. For a sinusoidal emf or current

**Chapter 14. Dual nature of radiation and matter**

(77) Threshold frequency.

Ans. The threshold frequency for a given metal surface is defined as the characteristic minimum frequency of the incident radiation below which no photoelectrons are emitted from that metal surface.

(78) Threshold wavelength.

Ans. The threshold wavelength for a given metal surface is defined as the characteristic maximum wavelength of the incident radiation above which no photoelectrons are emitted from that metal surface.

(79) Stopping potential.

Ans. The stopping potential is defined as the value of the retarding potential difference that is just sufficient to stop the most energetic photoelectrons from reaching the collector so that the photoelectric current in a photocell reduces to zero.

(80) Photoelectric work function.

Ans. The photoelectric work function of a metal is defined as the minimum photon energy that will eject an electron from the metal.

**Chapter 15. Structure of atoms and nuclei **

(81) Stationary (stable) orbit.

Ans. In the Bohr model of a hydrogen atom a stationary or stable orbit is defined as any of the discrete allowed orbits such that the electron does not radiate energy while it is in such orbits.

(82) Ground state of an atom.

Ans. Ground state of an atom is defined as the lowest stable energy state of the atom.

(83) Excitation energy of an atomic electron.

Ans. The energy required to transfer an electron from the ground state to an excited state (a state of higher energy) is called the excitation energy of the electron in that state.

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(84) Binding energy of an atomic electron.

Ans. Binding energy of an electron in an atom is defined as the minimum energy that should be provided to an orbital electron to remove it from the atom such that its total energy is zero.

(85) Ionization energy of an atomic electron OR Ionization energy of an atom.

Ans. Ionization energy of an electron in an atom is defined as the minimum energy required to remove the least strongly bound electron from a neutral atom such that its total energy is zero.

(86) Radioactivity.

Ans. Radioactivity is the phenomenon in which unstable nuclei of an element spontaneously distintegrate into nuclei of another element by emitting a particles, or particles, accompanied by y-rays.

(87) Half-life of a radioactive element.

Ans. The half-life of a radioactive element is defined as the average time interval during which half of the initial number of nuclei of the element disintegrate

(88) Decay constant or disintegration constant.

Ans. The decay constant or disintegration constant of a radioactive element is defined as the ratio of the disintegration rate at an instant to the number of undecayed nuclei of the element present at that instant.

(89) Mean-life of a radioactive element.

Ans. The mean-life of a radioactive element is the average time for which the undecayed nuclei of the element exist before decaying. It is equal to the reciprocal of the decay constant of that element.

(90) Nuclear fission.

Ans. Nuclear fission is a nuclear reaction in which a heavy nucleus of an atom splits into two or more fragments of comparable size either spontaneously or when bombarded by a neutron, with the release of enormous amount of energy.

(91) Nuclear fusion. Ans. Nuclear fusion is a type of nuclear reaction in which lighter

atomic nuclei (of low atomic numbers) fuse to form a heavier nucleus (of higher atomic number) with the release of enormous amount of energy.

(92) Chain reaction.

Ans. A chain reaction is a self-multiplying nuclear fission process in which neutrons ejected in one nuclear fission strike neighbouring nuclei of fissile material and cause more fissions

**Chapter 16. Semiconductor devices **

(93) Depletion layer (region).

Ans. The depletion layer or depletion region is the region of the junction between a p-type layer and an n-type layer within a single semiconducting crystal which is depleted of free charge carriers.

(94) Barrier potential.

Ans. The barrier potential is defined as the electric potential difference across the depletion region of a pn-junction.

(95) Rectification,

Ans. The process of converting an alternating voltage (or current) to a direct voltage (or current) called rectification