# Magnetic Effects of Electric Current | Activities in Text Book with Solution

Activity 13.5

Take a battery (12 V), a variable resistance (or a rheostat), an ammeter (0–5 A), a plug key, connecting wires and a long straight thick copper wire.

Insert the thick wire through the centre, normal to the plane of a rectangular cardboard. Take care that the cardboard is fixed and does not slide up or down.

Connect the copper wire vertically between the points X and Y, as shown in Fig. 13.6 (a), in series with the battery, a plug and key.

 Fig. 13.6
(a) A pattern of concentric circles. The arrows show the direction of the field lines. (b) A close up of the pattern

Sprinkle some iron filings uniformly on the cardboard. (You may use a salt sprinkler for this purpose.)

Keep the variable of the rheostat at a fixed position and note the current through the ammeter.

Close the key so that a current flows through the wire. Ensure that the copper wire placed between the points X and Y remains vertically straight.

Gently tap the cardboard a few times. Observe the pattern of the iron filings. You would find that the iron filings align themselves showing a pattern of concentric circles around the copper wire (Fig. 13.6).

What do these concentric circles represent? They represent the magnetic field lines.

How can the direction of the magnetic field be found? Place a compass at a point (say P) over a circle. Observe the direction of the needle. The direction of the north pole of the compass needle would give the direction of the field lines produced by the electric current through the straight wire at point P. Show the direction by an arrow.

Does the direction of magnetic field lines get reversed if the direction of current through the straight copper wire is reversed? Check it.

✅ Answer: The direction of magnetic field lines is reversed if the direction of current through the copper wire is reversed.