Let us study : WELCOME STUDENTS CLASS XII Let us study Chapter 1- Electric Charges and Fields Unit 1- Electrostatic SLM-2
Slide 2 : ELECTRIC CHARGES AND FIELDS
Slide 3 : Mind Map
Slide 4 : Two kinds of an entity developed when two bodies are rubbed with each other.
It may be positive or negative. ELECTRIC CHARGE
Slide 5 : KINDS OF CHARGES AND ELECTRIFICATION 1.Positive Charge
2.Negative Charge 1 Like Charges repel
2 Unlike Charges Attract - - ELECTRIFICATION
Slide 6 : OBJECTS ACQUIRING TWO KINDS OF CHARGES ON RUBBING
: POLARITY OF CHARGE The Property which differentiates the two kinds of charges.
The addition of similar types of charges results in net increase of charge while the addition of opposite types of charges results in the net decrease. CONDUCTORS AND INSULATORS Conductors The substances which allow the electric current to pass through them are called conductors.When some charge is given to a conductor then it gets distributed over the whole surface.
Examples: Silver, copper, iron etc.
Slide 8 : Insulators: The substances which do not allow the electric current to pass through them are called insulators.If some charge is put on an insulator,it stays at the same place. Insulators also called as Dielectrics.
Examples: Plastic, ebonite etc.
Slide 9 : CHARGING BY CONDUCTION Transfer of charge from one body to another by direct contact.
Slide 10 : The production of an unbalanced electric charge on an uncharged metallic body as a result of a charged body being brought near it without touching it. CHARGING BY INDUCTION
Slide 11 : CHARGING A METALLIC SPHERE BY INDUCTION (i) An uncharged metallic sphere on an insulating stand.
(ii) A charged glass rod near the sphere.Free electrons of the sphere are attracted and start pilling up near its end.This end becomes –vely charged and farther point +vely charged.
Slide 12 : (iii) When sphere is grounded,electrons flows from ground to sphere and neutralize the +ve charge on the farther end.
(iv) If the sphere is disconnected from the ground,-ve charge continues to be held on the near surface.
(v) When glass rod is removed,the –ve charge spreads uniformly over the surface.
Slide 13 : BASIC PROPERTIES OF ELECTRIC CHARGES 1.Additivity of electric charge:
If q1, q2, q3, ……,qn are charges in a system then total charge of the system is q1+ q2+ q3+ ……+qn.
Proper sign have to be used while adding the charges in a system.
Example: If a system contains charges +q,-2q,+3q,+5q,then total charge of the system is = +q -2q +3q +5q = +7q.
Slide 14 : 2. Law of conservation of charge: Total charge of the system always remains conserved.
It is not possible to create or destroy net charge carried by an isolated system.
Charges can be created or destroyed in equal and unlike pairs only.
Example:
92U238 ? 90Th234 + 2He4
Slide 15 : 3. QUANTISATION OF CHARGE:
All free charges are integral multiple of basic unit of charge denoted by ‘e’. Thus q = ne. Here n is an integer.
The value of basic unit of electric charge is 1.6 ? 10-19 Coulomb.
The reason of quantisation is that only integral number of electrons can be transferred from one place to another,on rubbing.
Slide 16 : COULOMB’S LAW DERIVATION Suppose two point charges Q1 and Q2 are placed in a vacuum at a distance R apart.
Slide 17 : According to Coulomb’s Law
Slide 18 : Force of attraction or repulsion between two point charges at rest is:
Directly proportional to the product of their charges.
Inversely proportional to the square of he distance between them. COULOMB’S LAW
Slide 19 : COULOMB’S LAW IN VECTOR FORM
Slide 20 :
Slide 21 : SUPERPOSITION PRINCIPLE The force acting on any charge due to a number of other charges at rest is the vector sum of all the forces on that charge due to due to the other charges, taken at a time.
Contd…
Slide 22 : If
F01= force on q0 due to q1
F02= force on q0 due to q2
F0n= force on q0 due to qn
Slide 23 : FORCE BETWEEN MULTIPLE CHARGES
Slide 24 : It is the region (three dimensional) around a charge in which its electrical influence can be realized. ELECTRIC FIELD
Slide 25 :
Slide 26 : Electric Field intensity due to a point charge:
Slide 27 : If several point charges q1,q2.......qn fixed at different points in space. Then, according to the superposition principle, the electric field E at a given point is the vector sum of the fields due to all the charges. FIELD DUE TO SYSTEM OF CHARGES
Slide 28 : We may define an electric field line as a path, straight or curved, such that tangent to it any point gives the direction of electric field intensity at that any point. ELECTRIC LINES OF FORCE
Slide 29 : PROPERTIES OF ELECTRIC LINES
OF FORCE 1.No two lines of force can intersect each other.
2.Electric field lines are always normal to the surface of conductor.
3.Electric field lines contract longitudinally. 4. Electric field lines exert lateral pressure.
5.Tangent to them gives the direction of force.
6.Electric field lines are discontinuous curves.
Slide 30 : The total number of electric lines of force over any closed surface. Electric Flux
Slide 31 : Charge distribution is given by Surface charge density ?, Linear charge density ? and volume charge density ?.
? = ?Q/?S
? = ?Q/?l
? = ?/?V CHARGE DISTRBUTION
Slide 32 : ELECTRIC FIELD INTENSITY DUE TO CONTINUOUS CHARGE DISTRIBUTION The total charge on q0
Slide 33 : Case-1 Electric field intensity for linear charge distribution:
Slide 34 : Case-2 Electric field intensity for surface charge distribution:
Slide 35 : Case-3 Electric field intensity for volume charge distribution:
Slide 36 : An electric dipole consists of a pair of equal and opposite point charges separated by some small distance. ELECTRIC DIPOLE
Slide 37 : FIELD OF AN ELECTRIC DIPOLE (Axial line) Considering an electric dipole of two point charges –q and +q,separated by distance 2a apart.We have to calculate the electric field intensity at point P on the axial line.
Here OP = r.
Slide 38 : Resultant intensity E at P is
Slide 39 : FIELD DUE TO AN ELECTRIC DIPOLE (EQUATORIAL LINE) From the figure,
If E1 is the electric field intensity at P due to charge –q at A, then E2 is the electric field intensity at P due to charge +q at B, then
Slide 40 : ELECTRIC DIPOLE IN AN UNIFORM EXTERNAL FIELD Considering an electric dipole with dipole moment Let this dipole be held in an uniform electric field E at an angle with the direction of E.
Slide 41 : Force on charge +q at A = qE
Force on charge -q at B = qE
Slide 42 : The forces are equal and parallel to each other.
Acts in opposite direction at different points.
So, they form the couple which rotates the dipole in anticlockwise direction.
Torque = force x arm of couple
Slide 43 : GAUSS’S LAW The total electric flux through any closed surface is equal to times the net charge enclosed by that
surface.Mathematically it can be expressed as
Slide 44 : Proof Of Gauss’s Law This is Gauss’s law.
Slide 45 : FIELD DUE TO INFINITE LONG STRAIGHT CHARGED WIRE Let ? be the uniform linear charge density,l and r be the length and radius of the right circular cylinder.
Slide 46 : Electric flux contributed by the curved surface of the cylinder is
Where r and l are radius and length of the cylinder.
Total electric flux through the cylinder
Charge in the cylinder= line charge density x length
According to gauss’s law,
Slide 47 : FIELD DUE TO A CHARGED INFINITE PLANE SHEET Total electric flux over the entire surface=2EdS
Total charge enclosed by cylinder = According to Gauss’s law
2EdS =
Slide 48 : FIELD DUE TO UNIFORMLY CHARGED SPHERICAL SHELL Outside shell:
According to Gauss’s theorem
Slide 49 : (b) On the surface (r=R):
(c) Inside shell:
E=0 (because q inside the shell is zero.)
Slide 50 : THANKS FOR CHOOSING EXTRAMARKS.COM