^Resistance of various geometries
Resistance of various geometries Relations 1 to 4 are across length & relations 5 is for radial flow. Above results are valid for uniform resistivity ρ only.
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^Electric resistance
Electric resistance Depends upon the nature of material, shape & size, physical state like temperature, pressure, type & extent of impurity etc. of conductor. However r depends upon all above factors except on shape & size.
^Ohm’s law
Ohm’s law (a) = constant called electrical resistance R, provided there is no change in the physical conditions like temperature, pressure & impurity etc. (b) = (Microscopic version) i.e. conductivity of a conductor is independent of electric field existing in the material over a wide range of field.
^The magnitude of the difference between the individual measurement and the actual or true value is called the absolute error in the
^The magnitude of the difference between the individual measurement and the actual or true value is called the absolute error in the measurement of that quantity. It is represented by The ratio of the absolute error to the actual quantity measured is called the relative error of the measurement. Relative error
^Resistivity of conductors (ρ)
Resistivity of conductors (ρ) Resistance per unit length per unit cross sectional area of a material is called its resistivity or specific resistance, for metals it is (a) . Its reciprocal is called conductivity or specific conductance (σ). Both ρ & σ are independent of length, thickness, & shape or geometry.
^Continuity equation for Conductors
Continuity equation for Conductors For a conductor of variable cross section = constant at all sections but drift speed varies inversely with area of cross section.
^Current mechanism in conductors
Current mechanism in conductors In metals about 10 29 m – 3 of free electrons (called average number density ‘n’ ) move randomly (disordered) in all directions (like motion of gas particles) with average thermal speed of about 105 m/s & collide randomly with the metal ions (almost fixed). Between the collision the free electrons […]
^Electric current (I) & current density (J)
Electric current (I) & current density (J) Electric current is the rate at which electric charge crosses a plane. i.e. mathematically, Current per unit area is called current density, i.e. mathematically, Electric current is scalar, while current density is vector. I & J are parallel to applied E – field.
^Wheatstone bridge
Wheatstone bridge The arrangement of five capacitors as shown is called Wheat stone bridge. If then points P & Q are at same potential & the bridge is said to be balanced, due to this no charge will flow in the arm PQ & hence arm PQ can be removed & circuit can becomes […]
^Kirchoff’s laws
Kirchoff’s laws 1st or junction rule: Σq = 0 at any isolated junction to conserve charge. 2nd or mesh rule: ΣV = 0 for any closed mesh to conserve energy. For shown circuit we can write At jn. A: – q1 + q2 + q3 = 0
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