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Magnetic Field Along The Axis of A Circular Coil Carrying Current



 Circular coil apparatus: 



The apparatus consists of a circular coil C of 5 to 50 turns, having diameter about 10 centimeters. There is a brass frame in which the coil is wound. The frame is fitted to a stand, with its plane vertical. It can be moved along a rectangular wooden board. B is the deflection magnetometer. There is a scale fitted to the wooden board, from which the distance of the centre of the magnetic needle from the centre of the coil can be measured.













Procedure for doing the real lab:


     To find the magnetic field:


The connections are made as shown in the diagram and the initial adjustments of the apparatus are made as follows:


  • First, the coil is fixed at the middle of the platform and the compass box is placed at the centre of the coil.
  • The compass box is rotated till the 90-90 line becomes parallel to the plane of the coil.
  • Then the apparatus as a whole is rotated till the aluminium pointer reads 0-0.
  • Close the circuit.
  • Adjust the rheostat until the deflection lies between 30 and 60 degrees. Note down the deflection of the compass needle and the current.
  • Then current through the coil is reversed using the commutator and again the deflection and current are noted.
  • Average the magnitude of the two deflections and calculate the magnetic field at the centre of the coil from the equation.
  • Without changing the current or the number of turns,  place the compass box at a particular distance from the centre of the coil. Note the deflection. Again reverse the current and average the magnitudes of the two deflections. Note the average, and the distance.
  • The same procedure is repeated with the compass box at the same distance on the other side of the arm, keeping number of turns and current constant.
  • Take the average of the two values of θ measured on opposite sides of the coil.
  • Then calculate the magnetic field Bx from the coil using equation (3).
  • Repeat for various distances.
  • Draw graph of Bx on the vertical axis vs. distance x on thehorizontal axis. 


       To plot the graph between distance and magnetic field intensity:


B0= 3.5x10-5 T.

Current, I = ……… A

No: of turns of the coil, n = …..

Radius of the circular coil, r = ….. cm.




Then plot the graph.


Procedure for doing the simulator:


First, the preliminary adjustment should be done in order to make the apparatus in the magnetic meridian.


  • First, preliminary adjustments should be done in order to properly align the apparatus with the earth’s magnetic field. The button Initial Adjustment is provided for this purpose. The experimental apparatus will be fully active only after the initial adjustments are done.


  • On clicking the initial adjustment button, a zoomed view of the compass box will be displayed in the simulator. Two sliders Rotate Compass box and Rotate apparatus are provided.


  • Using the slider Rotate Compass box, the compass box can be rotated and its 90-90 reading parallel to the plane of the coil. Fine adjustments can be made, if necessary, with the left-right arrow keys. 


  • When the 90-90 alignment is exact, the slider Rotate apparatus will be active. Using this, rotate the whole apparatus and make the aluminium pointer to read 0-0. Fine adjustments can be made with left-right arrow keys.


  • Using the Show normal button in the simulator, go back to the experimental set up.


  • Make the connections as shown in the circuit diagram. The user can drag the connection wires from the terminals of each components when a hand symbol appears there.


  • Close  the circuit using the button Insert key.


  • Zoom compass box enables the user to view the reading of the pointer.


  • Number of turns of the coil: The user can select the number of turns of the coil using this combo box. 


  • Reverse current: Enables the user to reverse the direction of current through the circuit.


  • Using the slider Radius of the coil, the user can change the radius of the coil.


  • The slider along with the compass box can be moved along the arm of the apparatus using the slider Compass box position. The user can vary the distance  of the compass box from the centre of the coil. 


  • Adjust Rheostat slider can be used to adjust the current throuh the circuit.


  • Show result button displays the result after doing the experiment.


  • A Reset button is provided to reset the experimental set up.  (Warning! all wires will be disconnected and the apparatus will be returned to its starting position.)


  • The experiment can be repeated for different number of turns and radius of the coil and for different currents.




 Flux density due to earths horizontal field at the place=..........T





Cite this Simulator:

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