Key relationship
m=NI A; τ=mB sinθ; U=−mB cosθ.
Physics · Class 12
Current-loop torque and moment
The magnetic moment points along the loop normal by the right-hand rule. A uniform magnetic field creates torque even though net translational force on the closed loop is zero.
Open the interactive experiment →Current-loop torque and moment
சுருளின் காந்த இருமுனைத் திருப்புத்திறன் NIA. சீரான புலத்தில் திருப்புவிசை உண்டு; நிகர இடப்பெயர்வு விசை பூஜ்யம்.
Key notes, relationships and model limits
Remember
The magnetic moment points along the loop normal by the right-hand rule. A uniform magnetic field creates torque even though net translational force on the closed loop is zero.
Common trap
The loop’s magnetic moment is normal to its plane. The torque angle is between that normal and the magnetic field.
Model limits
A rigid closed loop carries a prescribed current in a uniform external magnetic field. Field gradients, induced-current changes and mechanical losses are omitted.
What you will learn
Use the controls and plotted relation to explain current-loop torque and moment.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
A 100-turn, 100 cm² loop carrying 1 A has m=1 A m² and maximum torque 0.1 N m in 0.1 T.
Why this matters
The model connects current-loop torque and moment with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
Maximum torque occurs when the loop normal makes what angle to B?
- 0°, where the normal is parallel to B.
- 90°.
- 180°, where energy is greatest.
Read the explanation
90°.
Course connection: Class XII Chapter 4. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.