Simulation · Physics · Class 12
The field inside a solenoid
From the lesson The solenoid in Moving Charges and Magnetism. Change the values and watch what happens.
The field inside a solenoidPhysics · Class 12
The idea behind it
NCERT §4.7
- A solenoid is a long insulated wire wound as a closely spaced helix; a long solenoid is one whose length is much more than its radius. Each turn acts as a circular loop.
- Between neighbouring turns the fields cancel. Inside, the field is strong, uniform and along the axis; just outside it is weak, and for a very long solenoid it is taken as zero.
- A rectangular Amperian loop with one side h inside along the axis and one outside gives Bh = μ₀(nh)I, so B = μ₀nI, with n counting the turns in each metre of winding.
- The inside field does not depend on the radius or on the position inside, only on n and I. Its direction follows the right-hand rule.
- A solenoid is the usual way to make a uniform field; a soft iron core inside makes it much larger.
- Example 4.8: 500 turns on 0.5 m (n = 1000 per metre) with 5 A: B = 4π × 10⁻⁷ × 10³ × 5 = 6.28 × 10⁻³ T. The ratio of length to radius is 50, so the long-solenoid formula is fair.