Direct Resistance Heating Applications Explained

Direct resistance heating is a process where electrical energy is directly converted into heat by passing an electric current through the material or medium that needs to be heated. The heat generated is proportional to the resistance of the material and the square of the current flowing through it (Joule's Law: P = I²R).

Analyzing the Options

Let's examine how each option applies direct resistance heating:

• Electrode boiler: In an electrode boiler, water (or another fluid) acts as the resistive medium. Electric current is passed directly through the water between electrodes, generating heat and boiling the water. This is a clear example of direct resistance heating.
• Salt-bath furnace: This type of furnace heats a bath of molten salt. An electric current is passed directly through the molten salt, utilizing its electrical resistance to generate the required heat for the furnace.
• Resistance welding: This technique uses the heat generated from electrical resistance to join metals. A high electrical current is passed directly through the components being joined at the point of contact. The resistance at this interface causes localized heating and melting, forming the weld.

Conclusion on Direct Resistance Heating

As demonstrated above, electrode boilers, salt-bath furnaces, and resistance welding all utilize the principle of direct resistance heating by passing current directly through the substance being heated (water, molten salt, or the workpiece interface).

Therefore, since all the individual options are correct applications of direct resistance heating, the most appropriate answer is that all options are correct.