Magnetic Field due to current in solenoid

As we already discussed about the magnetic field around a circular loop. The magnetic field lines are straight at the centre of a loop but when we move towards end of loop, field lines become curved. What will happen if we place another circular conducting loop parallel to first? Will magnetic field lines become straight? The arrangement of such loop will study in the concept of solenoid.


  • Solenoid is used to produce magnetic field.
  • Solenoid is used in television as a source of magnetic field.
  • Solenoid are also used in a particle accelerator.
  • Solon means pipe, the structure of solenoid is like pipe.
  • Definition: Solenoid is a device in which number of an insulating copper wire circularly wound on a cylinder.
  • The diagram of solenoid is as


  • Sometimes we place soft iron core in the cylinder to increase magnetic field.
  • Connect a battery to the solenoid, it will produce magnetic field.


  • The magnetic field due to solenoid is as

  • This is the front view of solenoid. Current will pass perpendicular to plane of page.
  • Each dot and cross denote a point in which current will going out and going inside a plane of paper respectively so it produce magnetic filed around it.
  • At upper side, the current going out from the plane of paper so it is denoted by dot. The magnetic field linesdue to each dot are form a anticlockwise loop as shown in figure.
  • At lower side current, going inside the plane of paper so it is demoted by cross. The magnetic field lines form a clockwise cool as shown in figure.
  • Some materials has tendency to get permanent magnetized in the presence of external magnetic field such materials are called ferromagnetic materials. So solenoid is used to magnetized such materials.
  • Magnetic field due to solenoid is depend on the following factors

B = μ₀ N I /L


B – magnetic field

μ₀- absolute permeability

N – No of turns

L- length of solenoid

I – Current.

The solenoid is long a solenoid. If a solenoid is not long then its magnetic field is half than long solenoid.


Q) Why does we place soft iron core inside solenoid?

Q) What will be the change in magnetic field if we increase number of turns of a solenoid?

Q) On what factors the magnetic field of solenoid depend?

Q) How do you increase magnetic field of solenoid?

Q) what are uses of solenoid?

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