Key relationship
Fwire=BIℓ sinθ; Fparallel/ℓ=µ₀I₁I₂/(2πd).
Physics · Class 12
Wire force and parallel currents
An external B acts on a current-carrying wire. Two long parallel wires also exert forces on one another: agreeing current directions attract; opposite directions repel.
Open the interactive experiment →Wire force and parallel currents
ஒரே திசை இணை மின்னோட்டங்கள் ஈர்க்கும். எதிர்திசை மின்னோட்டங்கள் விலக்கும்.
Key notes, relationships and model limits
Remember
An external B acts on a current-carrying wire. Two long parallel wires also exert forces on one another: agreeing current directions attract; opposite directions repel.
Common trap
Parallel currents in the same direction attract; opposite directions repel. Force on a wire also depends on its angle to B.
Model limits
Long thin parallel wires with negligible end effects; positive mutual force denotes attraction.
What you will learn
Use the controls and plotted relation to explain wire force and parallel currents.
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
For 2 A and 3 A at 0.1 m separation, mutual force per metre is 12 µN/m.
Why this matters
The model connects wire force and parallel currents with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
Two parallel wires with opposite currents exert?
- Attractive forces because both wires carry current.
- Repulsive mutual forces.
- No forces because the wires are parallel.
Read the explanation
Repulsive mutual forces.
Course connection: Class XII Chapter 4. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.