Facts

• If the liberated mass doesn’t react with electrodes, the electrode is called inert otherwise soluble.
• Cu – anode with any metallic cathode in Cu –voltameter forms inert electrode.
• Platinum electrodes in water voltameter, Platinum anode in Cu – voltameter are the examples of inert electrodes.
• During electrolysis mass of cathode increases, (Reduction takes place at cathode) while that of anode decreases & concentration of electrolyte remains constant.
• Alternating current can’t be used in electrolysis. As the frequency of AC changes periodically, so there will be no deposition on any electrode actually.
• The back EMF or polarization EMF in water is 1.5 V. This is why to carry out electrolysis of H₂O we need a voltage greater than 1.5 V.
• Electrolysis is useful in, electroplating, extraction of metals from ores & their purification, electrolytic etching to mark logo, to produce H₂ and O₂ commercially, to separate non-metallic particles from the metallic ones, to ascertain the polarity of a battery, in finding equivalent weights & atomic weights.

Circuit to find ‘r’ of a cell

When the switch S is closed & the switch S₁ is kept open, then the cell of emf ξ is said to be in open circuit. Let here the balancing length is b₁, then ξ ∝ b₁ Now when the switches S & S₁ are closed, then the cell of emf ξ is said to be in closed circuit.

Let here the balancing length is b₂, then V ∝ b₂

Dividing above two relations we get

Fuse

A fuse is a thin wire made up of an alloy of lead (75 %) & tin (25 %). Both its resistance and melting point are low. It is connected in series to the circuit in to protect the circuit from sudden strong currents by breaking the circuit. When the rate at which heat produced by the current becomes equals to the rate at which heat lost by radiation, the temperature of the wire further stops increasing. This stage is called steady state, then rate of heat supplied = Rate of heat lost i.e.

(a) For constant ρ, T & T_s we can write I²  ∝ r ³, L⁰

(b) As T_S = 0 for vacuum & other terms are constants thus T ⁴ ∝ r ^{– 3} or T  ∝ r ^{– 3 / 4}