Electricity

• When a body loses electrons it is positively charged. When body gains electrons it is negatively charged. This happens in non conducting bodies which are static.
• When we rub 2 non- conducting bodies transfer of electrons take place.
• Example of non conducting bodies are silicon and glass
• SI unit of charge is known as coulomb
• When charge is lower than 1 coulomb

  • Millicoulomb - 10-³ C
  • Microcoulomb_ 10-⁶ C
  • Nanocoulomb _ 10-⁹ C
• Charge - scalar quantity
• Charge of an electron ~ -1.6 × 10-¹⁹ C
• The quantity of charge is determined by the number of electrons
• Q = ±ne

  Where n is the no. of electrons and e is charge of an electron
• n = 6.25 × 10¹⁸ electrons

  i.e 1 coulomb contains 6.25 × 10¹⁸ electrons.
• Electric current - Rate of flow of charge for a particular time
• i = q/t

  This is for tiny amount of charge
• If charge has n no. of electrons,  Total electric current can be written as

  I = Q/ t

  Where Q is the quantity of charge.
• I = Cs-¹

  Or the SI unit of current is called Ampere
• When 1 coulomb of charge flows through an area of cross section in a time period of 1 second, it is known as 1 Ampere.
• Electric current is measured by an Ammeter
• Electric current is measured by an Ammeter

  Note : Ammeter is always connected in a series circuit
• Current always flows from high potential to low potential
• The direction of flow of current is opposite to the direction of motion of electrons
• In metals only negatively charged electrons move.

  Although in electrolytes and ionised gases both cations and anions move.

  Electrolytes are found in batteries
• Current moving in electrolytes can be told as

  I = n¹q¹ + n²q²/t

  Where

  n¹=cations

  q¹ is cations charge

  n²= cations

  q² = anions charge
• In electrolytes cations and anion move in opposite directions.
• The work done to bring a unit positive charge from infinity to a point in the electric field is known as Electric potential.
• Electric potential


  Scalar quantity
• Electric potential is measured using a voltmeter
• $V=$$W /q$

  V is volt

  W is work done

  q is Electric charge
• Voltmeter is always connected in a parallel circuit
• Potential difference is the work done to bring a unit positive charge from one point to another within the circuit.
• SI unit of potential difference is volt
• $V_b - V_a =$$W/q$

  Where a and b are the two points I the potential difference.
• Resistance can be caused be collision of -ve and +ve ions
• the obstruction given to the flow of charge by the material is known as Resistance.
• SI unit of resistance is known as Ohm (Ω).
• • Nature of material
  • Temperature

  1. Conductor L is directly proportional to temp
  2. Semiconductor L is directly proportional to temp

  • Length of the conductor

  L is directly proportional to Resistance

  $R_1/R_2 =$$L_1/L_2$

  If R¹ and R² are made of the same material

  • Area of cross section (a)

  R is inversely proportional to a

  $R_1/R_2 =$$a_2/a_1$

  $R_1/R_2 =$$(r_2)^2/(r_1)^2$
• Conductance is the reciprocal of Resistance
• G = 1/R

  Unit = 1/ ohm

  = Ohm -¹

  =mho

  = Seimen
• Resistance of wire of that material of unit length and unit area is known as Specific Resistance
• Specific resistivity depends on the factors

  • Characteristics / nature of material
  • Temperature
• R & L (& is directly proportional)

  R& 1/a

  R = p×L/a

  Where p is row and specific resistivity if L and a are 1
• Difference between Resistance and resistivity

  Resistance is not constant

  Resistivity is constant when L and a are 1 at given temperature.