Title 1. OLYMPIAD CURRENT ELECTRICIT WS VOL-1.pdf ✅

X– Physics (Vol – I) Olympiad Classwork CURRENT ELECTRICITY Essentials from static electricity: Charge: It is an intrinsic property of the sub atomic particles to attract or repel the other. • Charge is responsible for electric force. • Charge is of two types i.e., positive and negative. • Charge is measured in coulomb (in SI). • Charge of electron (e) is 19 1.6 10  coulomb of negative charge. Like charges repel and unlike charges attract. The charge on a charged body (Q) is given by Q ne   , where n is an integer, n cannot be a fraction. Force between two charges: If two charges 1 q and 2 q are separated by a distance ‘r’ the force of attraction or repulsion between them is given by 1 2 2 1 4  q q F  r 2 9 2 0 1 9 10 4   Nm  C 0  is permittivity of Vacuum.  is permittivity of the medium. Electric field intensity (E): The effective region around a charge is called electric field. ‘The force experienced by a unit positive charge at a point in the electric field is called electric field intensity at that point’. 0 F E q  , where 0 q is the test charge. SI unit of E is N C , it is a vector physical quantity.
Olympiad Classwork X – Physics (Vol – I) Electric Potential difference between two points (V): The amount of work done to move unit positive charge from one point to an other in an electric field is called the electric potential difference between the points. w V q  Relation between electric field intensity E and potential at a point: If E ur is the electric field and V is the potential at a point then the relation among them is given by V E dl     ur uur For uniform electric field v E l     , where l is the distance in the electric field where a potential difference v is developed. Properties of Electric Current: I) Strength of Electric Current: II) Applications on electric current. III) Current Density IV) Relaxation time V) Drift velocity VI) Mobility Introduction: In our daily life we listen to music on a tape recorder or radio receiver, see different programs on television, enjoy cool breeze from electric fan or cooler. Do you know, what makes these appliances work? It is electric current. Electricity is a unique gift of science to mankind. Our everyday life is governed directly or indirectly by many applications of electricity. We cannot imagine to live without electricity in the modern world. I. Strength of electric Current: When a potential difference is applied across a conductor an electric field sets in the conductor and electrons drift in the direction opposite to the field. Due to electron drift, charge flows through the conductor and we say that the electric current is flowing through it. The direction of current is taken opposite to the direction of flow of electrons (negative charge) and in the direction of flow of positive charge. Let a charge Q be passing across a conducting wire in a short time interval t then, electric current is Q I t    If a net charge ‘Q’ passes through any cross section of the conductor in time ‘t’ then the average current ‘I’ is given by
X– Physics (Vol – I) Olympiad Classwork Avg  Q I t The electric current through any conductor is the rate of transfer of charge from one side of any cross section of conductor to the other side. The SI unit of current is ampere (A) Definition of Ampere: If one coulomb of charge passes through a cross section of the conductor per second then the current is said to be one ampere. i.e., 1Coulomb(C) 1 Ampere(A)= 1Second(s) Commonly used sources of electric current are electric cells, electric generators etc. If the rate of flow of charge with time is not constant, the instantaneous current is defined by the equation,   0    t  Q dQ I Lt t dt Current is a scalar quantity. It is a macroscopic quantity like the mass of a body or volume of a container. In SI units, current is one of the fundamental physical quantity. It is dimensionally denoted by [I] or [A]. II) Applications on electric current: 1. If the current is varying with time t, then the charge flowing in a time interval from 1 t to 2 t is 2 1 t t q Idt   W.E-1: The current through a wire depends on time as 0 i i t   , where 0 i A 10 and   4 / A S . Find the charge that crossed through a section of the wire in 10 seconds. Sol: 0 i i t   ; but dq i dt  dq i t dt    0   10 10 2 0 0 0 2 t t t q dq q i t                 10 50 i 0   = 300 coulomb 2 If n particles, each having a charge q, pass through a given cross sectional
Olympiad Classwork X – Physics (Vol – I) area in time t, then average current is nq i t  . 3 If a point charge q is revolving in a circle of radius r with speed v then its time period is   2      r T v  . r q V 4 The average current associated with this revolving charge is 2 2 q w vq I fq q T r       Where f is the frequency of revolution in Hz,  is the angular frequency in rad/sec, v is the linear velocity of the charge q, r is the radius of the circular path. W.E-2: In a hydrogen atom, electron moves in an orbit of radius 11 5 10 m   with a speed of 6 2.2 10 /  m s. Calculate the equivalent current. Sol: Current . 2    v i f e e  r = 6 19 11 2.2 10 1.6 10 2 5 10         = 3 1.12 10 amp   =1.12 mA In a discharge tube 1 n protons are moving from left to right in t seconds and 2 n electrons are moving simultaneously from right to left in t seconds, then the net current in any cross-section of the discharge tube is     n n e 1 2 I from left to right t  