Magnetic units – what physical quantity is measured in Tesla (T)? Identify the electromagnetic quantity for which the SI unit Tesla (T) is used.

Introduction / Context:
Correct units link physical intuition to formulas. In magnetics, we distinguish between magnetic flux Φ (weber), magnetic flux density B (tesla), magnetic field strength H (ampere per metre), and magnetomotive force (ampere-turns). This clarity is essential for interpreting datasheets and designing magnetic circuits.

Given Data / Assumptions:

• SI base and derived units are used.
• Magnetic flux density B relates to flux per unit area.
• Flux Φ and field strength H have different units from B.

Concept / Approach:

The Tesla (T) is defined as 1 weber per square metre. It measures magnetic flux density B, i.e., how much magnetic flux passes through a unit area. This is distinct from H, which has units A/m and describes the magnetizing field, and from Φ (Wb), the total flux threading a surface.

Step-by-Step Solution:

Verification / Alternative check:

Permanent magnets are often specified in tesla for surface flux density (e.g., 0.3–1.4 T), and MRI systems in tesla for field intensity of the B field experienced by spins.

Why Other Options Are Wrong:

Flux uses weber; field strength (H) uses A/m; MMF uses ampere-turns; reluctance uses inverse henry. Hence only 'flux density' is correct.

Common Pitfalls:

Interchanging B and H or assuming tesla measures 'field strength' generically; forgetting that B incorporates material response via B = μ0 μr H.

Final Answer:

flux density