• Electric current is expressed as the amount of charge flowing through a particular cross section
  0area in unit time.
• A multi-meter is an electronic measuring instrument that combines several measuring functions
  (electric potential difference, electric current and electric resistance) in one unit.
• Ohms law: The current through a conductor element is proportional to the potential difference
  applied between its ends, provided the temperature remains constant. Mathematically V=IR.
• Ohm’s law is valid for metal conductors at constant temperature. It is not applicable for gaseous
  conductors and semiconductors.
• Resistance is the opposition that a substance offers to the motion of electrons.
• Resistance of a wire depends on the material of the wire, its length and its area of cross section
  Rα l/A.
• The resistivity of a material is the resistance per unit length of a unit cross section of the material.
• Two or more resistors are said to be connected in series if the same current flows through them.
• The junction law: At any junction point in a circuit where the current can divide, the sum of the
  currents into the junction must equal the sum of the currents leaving the junction.
• The loop law: The algebraic sum of the increases and decreases in potential difference across
  various components of a closed circuit loop must be zero.
• Electric power is the product of potential difference and the current. SI unit of power is watt (W).
• Electrical energy is the product of power and time. Units of electrical energy W-s and KWH.

1. Explain how electron flow causes electric current with Lorentz – Drude theory of electrons.(AS₁)

2. Write the difference between potential difference and emf.(AS₁)