PHYSICS PRACTICAL (CBSE) - X Scientific Terminology / Definitions Absolute refractive index (m) : It is the refractive index of the medium with respect to air or vacuum. Amplitude (A) : It is the maximum displacement of the particles of the medium from their original undisturbed position. It is measured in cm/m. Angle of incidence : It is the angle between the incident ray and the normal. Normal Incident ray Angle of Incidence i 0 r Reflected ray Angle of Reflection Reflecting surface Angle of reflection ( r) : It is the angle between the reflected ray and the normal. Angle of refraction ( r) : The angle between the refracted ray and the normal. Angle of emergence (e) : The angle which emergent ray makes with the normal at the point of emergence. 1
Buoyancy/upthrust : It is the upward force experienced by the immersed body when partly or wholly immersed in a fluid. It is measured in newton. Crests : It is the elevation in a transverse wave. Compressions (C) : The part of a longitudinal wave where the particles of the medium are closer to one another. Coulomb (C) : It is the S.I. unit of charge. One coulomb is that quantity of electricity which flows through any cross-section of a conductor in one second. Conductors : Materials through which electric current can flow. e.g. Copper, Silver, Aluminium etc. Centre of curvature (C) : It is the centre of the sphere of which the mirror or lens is a part. Denser medium : A medium in which the speed of light is less or whose density is more. e.g. Glass is denser than water, water is denser than air Echo : It is the repetition of sound caused by the reflection of sound waves. Electromagnetic waves : The waves which do not require any material medium for 2
their propagation. e.g. Light waves, radio waves etc. Electric Circuit : A continuous path consisting of conducting wires and different appliances between the terminals of a battery along which an electric current flows. Electric current (I) : It is the rate of flow of electric charge. It s S.I. unit is ampere (A). E.m.f. of a cell (e) : (Electromotive force). It is the maximum potential when cell is not in use. Its S.I. unit is volt (V). Frequency(f) : It is the number of waves per second. Its S.I. unit is hertz (Hz). Focal length of a lens (f) : It is the distance between the principal focus and the optical centre. F is positive for concave lens and is negative for convex lens. Focal length of a mirror (f) : The distance between the pole and principal focus of the mirror. It is measured in cm/m. f is negative for concave mirror and positive for convex mirror. Focal length of a lens (f) : Distance between the optical centre and the principal focus. It is measured in centimetre or metre. Infrasonics : Sound waves having frequency less than 20 Hz. Insulators : Materials through which electric current cannot flow. e.g. Plastic, Rubber, Wood etc. Irregular reflection / Diffused reflection : Reflection of light in different direction when falls on rough surface. Incident ray : The ray of light which falls on the reflecting or refracting surface. 3
Lateral Displacement (D) : The shift in the path of light on emergence from a medium with parallel faces. Lateral displacement depend upon the thickness (t) of the glass slab. i.e. D t for a given angle of incidence. Light : It is the form of radiant energy which enables us to see the objects from which it is reflected. Longitudinal waves : It consists of compressions and rarefactions. In this types of waves the particles of the medium vibrate parallel to the direction of wave. e.g. Sound waves in air. Lateral inversion : In the mirror, in the image of the object the left side of object appears as its right side and vice versa. Mechanical waves / Elastic waves : Those waves which require material medium (solid/liquid/gas) for their propagation. e.g. Sound waves. Normal : ; A perpendicular drawn at the point of incidence. Non-ohmic conductors : Those conductors which do not obey the ohm s law. Its V-I graph is curved. e.g. Diode-valve. 5
Optical centre (O) : A fixed point inside the lens where a line drawn through the aperture meets the principal axis. Ohmic Conductors : Those conductors which obeys ohm s law. Its V-I graph is a straight line. Principal axis of a lens : A straight imaginary line joining the centre of curvatures of two spherical surfaces of the lens and passing through the optical centre of the lens. Power of a lens (P) : It is the reciprocal of the focal length (in metre) of the lens. P = 1 f Its S.I. unit is Dioptre (D) Principal focus of a mirror : The point on the principal axis where the parallel rays of light meet or appears to diverg after reflection. Principal axis of a mirror : It is the straight line passing through the pole and the centre of curvature of the mirror. Pole of a mirror : It is the centre of the reflecting surface of the spherical mirror. Point of incidence (O) : The point where the incident ray strikes to the reflecting or refracting surface. Potential difference (V) : The potential difference between the two point in an electric field is the amount of work done in moving a unit +(ve) charge from one point to another 5
point. i.e. Potential difference V = W Q. Its S.I. unit is volt (V) Pulse : A wave of short duration set up by a single disturbance in the medium. It is repetitive in nature. Rarer medium : A medium in which the speed of light is more or whose density is less. e.g. Air is rarer than water : water is rarer than glass. Reflected ray : The ray of light which is turned back by the mirror. Refracted ray : ;A ray of light which deviates from its path on entering in another optical medium. Refraction of light : The bending of light when passes from one medium to another medium. Radius of curvature (R) : It is the radius of the sphere of which mirror or lens is a part. Real image : It is the image of the object formed if the rays actually meet at a point after reflection or refraction. It can be obtained on a screen. Reflection of light : It is the turning back of light in the same medium after striking the reflecting surface. 6
Regular reflection : Reflection of light along a definite direction when falls on highly polished and smooth surface. Resistance (R) : It is the property of a conductor due to which it opposes flow of current through it. Its S.I. unit is ohm (W). Rarefactions (R) : The part of the longitudinal waves where the particles of the medium are farther apart than normal. Refraction of light : It is the change in direction of light when it passes from one medium to another. Reflection of sound : The bouncing back of sound when it strikes the hard surfaces such as wall. Specific heat of a substance : It is the quantity of heat required to raise the temperature of unit mass of a substance by unit C. Troughs : It is the depression in a transverse wave Time period (T) : It is the time required to produce one complete wave. It is measured in second (s). Transverse waves : It consists of crests and troughs. In this waves the particles of 7
the medium vibrate right angles to the direction of wave. e.g. Light waves Temperature : The quantity which helps in measuring the degree of hotness or coldness of a substance. Its S.I. unit is kelvin (k). In C.G.S. system its unit is degree celsius ( C). Ultrasonics : Sound waves having frequency greater than 20,000 Hz. Virtual image : It is the image of the object formed if the rays do not actually meet at a point but appear to meet after reflection or refraction. It cannot be obtained on a screen. Wavelength (l) : It is the distance between the two consecutive crests or between two consecutive troughs in transverse waves and between two consecutive compressions or between two consecutive rarefactions in longitudinal waves. It is measured in cm/m. 8