PhysicsGutka

(6) Magnetic force on a current carrying wire We know that current flowing in a conductor is nothing but the drift of free electron's from lower potential end of the conductor to the higher potential end when a current carrying conductor is placed in a magnetic field ,magnetic forces are exerted on the moving charges with in the conductor Equation -1 which gives force on a moving charge in a magnetic field can also be used for calculating the magnetic force exerted by magnetic field on a current carrying conductor (or wire) Let us consider a straight conducting wire carrying current I is placed in a magnetic field B(x).Consider a small element dl of the qire as shown below in the figure Drift velocity of electrons in a conductor and current I flowing in the conductor is given by I=neAv d Where A is the area of cross-section of the wire and n is the number of free electrons per unit volume Magnetic force experienced by each electron in presence of

(5) Cyclotron Cyclotron is a machine for producing high energy particles ,first developed by E.O.Lawrence and M.S.Livingston in 1931.Figure below shows the path of a charged particle in a cyclotron Construction cyclotron consists of two horizontal D-shaped hollow metal segments D 1 and D 1 with a small gap between them These D'ees are placed in between the poles of a large electromagnet so that that magnetic field is Perpendicular to the plane of the D'ees The whole space inside the D'ees is evacuated to pressure of about 10 -6 mm of Hg An ion source S is kept at the center between the D'ees The two D'ees are connected to the terminals of high freqency oscillating A.C circuit.This changes the charge of each D'ees several million time per sec Theory and working Suppose that any instant ,alternating potential is in the direction which makes D 1 positive and D 2 negative A positive ion starting from source S will be attra

(1) Introduction We have allready studied about thermal effects of current and now in the present chapter we are studied about magnetic effect of current. Earlier it was believe that there is no connection between electric and magnetic force and both of them are completely different. But in 1820 Oersted showed that the electric current through a wire deflect the magnetic needle placed near the wire and the direction of deflection of needle is reversed if we reverse the direction of current in the wire. So, Oersted's experiments establishes that a magnetic field is assoiated with current carrying wire. Again if we a magnetic needlle near a bar magnet it gets deflectid and rests in some other direction. This needle experiences the tourque which turn the needle to a definite direction. Thus, the reagion near the bar magnet or current carrying where magnetic needle experience and suffer deflection is called magnetic field. (2) The Magnetic Field We all ready

9. Electric Dipole Electric dipole is a pair of equal and opposite charges, +q and -q, separated by some distance 2a. Total charge of the dipole is zero but electric field of the dipole is not zero as charges q and -q are separated by some distance and electric field due to them when added is not zero. (A)Field of an electric dipole at points in equitorial plane We now find the magnitude and direction of electric field due to dipole. P point in the equitorial plane of the dipole at a distance r from the centre of the dipole. Then electric field due to +q and -q are $$\boldsymbol{E_{-q}}=\ frac {-q\boldsymbol{\widehat{P}}}{4\pi \epsilon _{0}(r^{2}+a^{2})} ( 1 a ) \boldsymbol{E_{+q}}=\frac{q\boldsymbol{\widehat{P}}}{4\pi \epsilon _{0}(r^{2}+a^{2})}$$                                          (1b) and they are equal Pˆ = unit vector along the dipole axis (from -q to +q) From fig we can see the direction of E +q and E -q . Their components normal to dipole cance

5. Principle Of Superposition Coulomb's law gives the electric force acting between two electric charges. Principle of superposition gives the method to find force on a charge when system consists of large number of charges. According to this principle when a number of charges are interacting the total force on a given charge is vector sum of forces exerted on it by all other charges. This principle makes use of the fact that the forces with which two charges attract or repel one another are not affected by the presence of other charges. If a system of charges has n number of charges say q 1 , q 2 , ...................., q n , then total force on charge q 1 according to principle of superposition is F = F 12 + F 13 + .................................. F 1n Where F 12 is force on q 1 due to q 2 and F 13 is force on q 1 due to q 3 and so on. F 12 , F 13 , .................. F 1n can be calculated from Coulomb's law i. e. F 12 = k q 1 q