In electromagnetism, what is the SI unit of the physical quantity "inductance"?

Introduction / Context:
Inductance is an important concept in electromagnetism and circuit theory, especially in circuits containing coils and inductors. It measures the ability of a conductor or coil to oppose changes in current by inducing an electromotive force (emf). The SI system assigns a specific unit to inductance, named after a famous scientist. This question asks you to identify that unit.

Given Data / Assumptions:

• Inductance appears in formulas relating magnetic flux, current and induced emf.
• The symbol for inductance is usually L.
• Other magnetic quantities include flux (measured in weber) and flux density (measured in tesla).
• Capacitance has the unit farad.

Concept / Approach:
For a coil, inductance L is defined by the relationship Φ = L * I, where Φ is the magnetic flux linked with the coil and I is the current through it. Inductance also appears in Faraday law of induction, where the magnitude of induced emf is proportional to the rate of change of current multiplied by inductance. The SI unit of inductance is the henry (H). One henry is defined as the inductance of a circuit in which an emf of one volt is induced when the current changes at the rate of one ampere per second.

Step-by-Step Solution:
Step 1: Recall the definition Φ = L * I, so L = Φ / I. Step 2: The unit of magnetic flux Φ is the weber (Wb), and the unit of current is ampere (A). Step 3: Therefore, the unit of L is Wb/A. Step 4: This derived unit is given the special name henry (H). Step 5: Compare to farad (F), which is the unit of capacitance, not inductance. Step 6: Tesla (T) measures magnetic flux density (Wb/m²), and weber alone measures magnetic flux, not inductance.

Verification / Alternative check:
Inductor specifications in circuit diagrams and data sheets use values like 10 mH, 100 µH or 1 H, where mH and µH stand for millihenry and microhenry respectively. Formulas such as energy stored in an inductor E = (1/2) * L * I^2 explicitly show L carrying units of henry when current is in amperes and energy in joules, which is consistent with the definition.

Why Other Options Are Wrong:
Weber (Wb): This is the unit of magnetic flux, not of inductance.

Farad (F): This is the unit of capacitance, used for capacitors, not for inductors.

Tesla (T): This is the unit of magnetic flux density (Wb/m²), not of inductance.

Common Pitfalls:
Students sometimes confuse magnetic flux (weber) with inductance (henry) because both occur in similar formulas, or they mix up henry and farad since inductors and capacitors often appear together in AC circuits. A good way to remember is to associate henry with inductors and coils, and farad with capacitors and stored charge.

Final Answer:
The SI unit of inductance is the henry (H).