| 1 |
What is electricity, static electricity? Charges are of two types....
etc... etc... etc....
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You all know this basic stuff by now..
No point wasting time on such basic ideas
Let's move on to other important things
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| 2 |
Charge is conserved (remember conservation of momentum!) |
Charge cannot be created or destroyed |
| 3 |
Charge is relativistically invariant |
Charge does not change with velocity
(remember how mass changes with velocity)
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| 4 |
Charge has quantum nature, with the smallest unit being e |
e = 1.6x 10-19 C (charge on an electron) |
| 5 |
Coulomb's Law
Force is directly proportional to the product of charges, inversely proportional to square of distance between them. Notice the similarity with the formula for gravitational force.
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| 6 |
Electric Field |
A region in which a charged particle experiences
a force |
| 7 |
Electric Field Strength |
Force experienced by a unit positive charge at a point |
| 8 |
Properties of lines of force:
They diverge (start) from a positive charge and converge (end) at a negative charge
They are closer together in regions where the field is stronger and further apart where the field is weak.
They begin and end perpendicularly to the charged surface
They never cross.
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The lines of force are always directed from higher to lower potential
the field is continuous, while they are drawn as lines at discrete
intervals
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| 9 |
Charge is a scalar quantity.
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Force is a vector quantity
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| 10 |
The presence of a charge creates an electric field in space, the strength of which is a vector quantity.
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The force between two positive charges is directed along the line
joining these charges. |
| 11 |
If the sign of the charges is included in calculations of the force between two charges using Coulomb's Law, then the forces which have a negative sign are attractive and those which have a positive sign are repulsive.
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Opposite charges attract, same charges repel |
| 12 |
Strength of Field due to an electric charge
Strength of field due to a group of point charges
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E = F/q0
E = E1+E2+E3+..... (Remember this is a vector addition.
Do not add them directly. Do not forget the cos_theta !)
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| 13 |
Electric Flux
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Flux is a measure of the number of field lines passing through an
area.
Φ E = E · A = E A cos(θ)
where θ is the angle between the electric field and the area vector.
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| 14 |
Gauss Theorem |
The net electric flux through a closed surface = 1/ε0 times net charge enclosed within |
| 15 |
Electric Potential (at a point) |
Work done to move a unit positive charge from infinity to that
point |
| 16 |
Electric potential at a point |
V(r) = q / 4 π&epsilon0 r |
| 17 |
Electric Dipole
Two equal and opposite charges separated by by a distance 2l
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Dipole Moment p = q x (2l) Note that entities in bold are vectors. The direction is from negative to positive charge. |
| 18 |
The torque on a adipole in a uniform electric field |
τ = pE sin&theta |
| 19 |
Work done in rotating a dipole through angle &theta from equilibrium |
W = pE(1 - cos &theta) |
| 20 |
Potential energy of dipole |
U = - pE cos &theta |
| 21 |
Electric potential energy between two point charges (1 and 2) |
U12 = q1q2 / 4 π&epsilon0 r12 |
| 22 |
Electric potential energy for a system of charges (lets say 3 charges 1,2, and 3) |
U = U12 + U13 + U23 |
| 23 |
Electric field due to a dipole |
The total electric field due to the dipole is the vector sum of the fields due to each charge at any location.
(Tip: Do not forget cos &theta )
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| 24 |
Some interesting cases that you must consider for exam |
Electric field and potential due to a charged spherical conductor/non-conductor: inside/ on surface/ outside
Motion of a charged particle in an electric field (Remember Force = mass X acceleration = qxE)
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The topics covered in this section are written in a language to cover more important concepts in minimum time.
