current | resistivity | Current electricity | ohm law | electric current | physics

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Current electricity and ohm's law(Current electricity) :- •What is current? Rate of flow of electric charge with time through any cross section of a wire is called current. It is denoted by I . Thus if charge "dq" flows through a wire in small time "dt" then electric current through wire is given by :                                             I=dq/dt  1 ampere = 1coulomb/1 second  1A=C/s •Ampere :-                                                           The current Through a wire is called one ampere if one coulomb charge is flow through Any cross section of wire in one second   •Ohm's law:- Ohm’s principal discovery was that the amount of electric current through a metal conductor...
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Capacitor and Expression of parallel plate capacitor |electrostatic | physics

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Capacitor and It's Expression (Electrostatics)  


What is capacitor? 

An arrangement for storing large amount of electric charge in small space is called capacitor. 

Principal of capacitor :-

A capacitor works on the principal, "The capacity of an insulated charged conductor is increased appreciate by bringing near it an earth connected, unchanged  conductor

Definition of capacitance :-

Capacitance of a conductor may be defined as the ratio of the electric charge on it to it's electric potential due to that charge 
                            C=Q/V

Expression for parallel plate capacitor :-

Let the two plates are kept parallel to each other separated be a distance d and cross-sectional area of each plate is A.  
We konw that,
                    C= Q/V

According to the gauss law, the electric field can be written as:-
Since we know that the capacitance is defined as V = Q/C, so capacitance can be rewritten as:-
                   

• Some important board exam level question answers :- 


Q. 1) Why capacitance becomes less in series combination ?

Ans:- In Series combination, the distance between the first and last conductors increases.
As C ∝ 1/d , capacitance decreases. 


Q. 2) Define capacitance. Give its SI unit. 

Ans:- Capacitance is defined as the ratio between charge on capacitor to its potential. If q is charge, V the potential, then C = q/V .
si unit of C = coulomb /volt =C/V or farad(f) .

Q. 3) why capacitance becomes more in parallel combination  ?

Ans:- In parallel combination the effective surface area (A)  of the conductor increases, As C ∝ A, the capacitance increases. 

Q. 4) Can we give any desired amount of charge to a capacitor  ?

Ans:- No, maximum charge given to a capacitor is limited by the dielectrics strength of the medium between the two plates of the capacitor. 

Q. 5) Define the SI unit of capacitor ?

Ans:- 1 Farad capacitor, when changed with 1 coulomb of electric charge, has a potential difference of 1 volt between it's plates. 










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Physics

Electric lines of force (electrostatic) | electostatic | physics

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 •  Electric lines of force        (Electrostatics)  1. The electric lines of force start from positive charge and end at negative charge.      2.  The lines of forces originate or terminate at a surface is always right angle to that surface. 3. The lines of forces never intersect each other. 4. The electric lines of force do not pass through a conductor. 5.Like charges repel each other wherever unlike charges attracted each other  • Some important Question Answer From Board level Exams:- Q. 1) Why electric field lines of force cannot intersect each other?   Ans:- This is because at the point of intersection, two tangent would have to be drawn to the lines of Force. Therefore would be two directions of electric intensity at the same point, which is not possible.  Q. 2) Write Two properties of electric field lines of force?  Ans:-    1. The lines of forces ...
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current | resistivity | Current electricity | ohm law | electric current | physics

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Image
Current electricity and ohm's law(Current electricity) :- •What is current? Rate of flow of electric charge with time through any cross section of a wire is called current. It is denoted by I . Thus if charge "dq" flows through a wire in small time "dt" then electric current through wire is given by :                                             I=dq/dt  1 ampere = 1coulomb/1 second  1A=C/s •Ampere :-                                                           The current Through a wire is called one ampere if one coulomb charge is flow through Any cross section of wire in one second   •Ohm's law:- Ohm’s principal discovery was that the amount of electric current through a metal conductor...
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Electric field (electrostatic) | electostatic | physics

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Electric field (Electrostatics)  . The space around a charge in which any other charge is acted upon by an electrostatic force is called electric field of charge .                   E = F/q.                  We know that,           F = k Qq. / r 2            Therefore                 E = k Qq. / r 2 *1/q.                      E =kQ/ r 2   The charge "Q" due to which electric field is set up is called source charge and the other charge "q." which experience electrostatic force in the electric field is called test charge . Electric field intensity :- The electric field intensity or electric field strength at a point due to a source charge may be defined as the electrostatic force per unit positive charge a...
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State and prove the Gauss's Theorem (electrostatic) | electostatic | physics

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Gauss’s Theorem (Electrostatic)   Statement:- According to Gauss’s theorem the net-outward normal electric flux through any closed surface of any shape is equivalent to 1/ε0 times the total amount of charge contained within that surface. Proof of Gauss’s Theorem Statement:- Let the charge be = q Let us construct the Gaussian sphere of radius = r Now, Consider , A surface or area ds having ds (vector) Normal having the flux at ds: d e = E (vector) d s (vector) cos θ But , θ = 0 Therefore, Total flux: C = f d Φ E 4 π r2 Therefore, σ = 1 / 4πɛo q / r2 × 4π r2 σ = q / ɛo • Some important board exam level question answers:- Q. 1) Write Gauss's theorem for a charge outside a closed surface.  Ans:- The theorem becomes zero.  Q. 2) What is an equipotential surface ? Ans:- A surface, which has same electric   potential everywhere on it is called   equipotential surface.  Ask me qu...
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