Induction furnace fundamentals: In a low or standard frequency induction furnace, heat generation within the charge primarily results from which phenomena?

Introduction / Context:
Induction furnaces heat electrically conductive charges by inducing eddy currents via an alternating magnetic field. The distribution of those currents and the associated ohmic losses determine how efficiently a charge is heated. Frequency selection affects penetration depth and the skin effect, which concentrates current near the surface.

Given Data / Assumptions:

• “Low/standard frequency” implies deeper penetration than high-frequency units.
• Charge is electrically conductive (metals), so eddy-current heating dominates; hysteresis may contribute only while the material is ferromagnetic and below Curie temperature.
• No external resistance elements are used.

Concept / Approach:
Heating power P is generated by I^2 * R of induced eddy currents. The skin effect (frequency-dependent) alters current distribution, modifying effective resistance and heating rate near the surface. Together, induced currents (source) and skin effect (distribution) describe the principal heating mechanism for metallic charges in induction furnaces.

Step-by-Step Solution:
Recognize primary mechanism: electromagnetic induction creating eddy currents.Account for frequency influence: skin effect concentrates currents, affecting where heat is produced.Select the option that mentions both phenomena: “Combination of induced currents and skin effect”.

Verification / Alternative check:
Design equations for induction melting include penetration depth δ ∝ 1/√f and power factors incorporating resistivity and geometry, explicitly reflecting induction plus skin effect.

Why Other Options Are Wrong:
Induction without skin effect: incomplete; distribution strongly affects heating.External elements: that would be a resistance furnace, not induction.Dielectric losses: apply to non-conductors (dielectric heating), not conductive metals.Only hysteresis: minor and disappears above Curie temperature; not the main mechanism.

Common Pitfalls:
Overstating hysteresis in metal melting and ignoring frequency-dependent penetration, which is central to sizing and power delivery.

Final Answer:
Combination of induced currents and skin effect