(a) Without using a magnet, magnetic field can be produced by flowing the current through a straight conductor or a solenoid.
Aim : To show that magnetic field exerts a force on a current carrying conductor. Apparatus required : Aluminium rod, stand, strong horse shoe magnet, cell, key and connecting wires.
A Current carrying rod PQ is experiencing force F
Procedure :
(i) Hang the aluminium rod with the help of clamp stand such that it passes between the North and South pole of the magnet with the magnetic field directed upwards and the rod being horizontal and perpendicular to the field.
(ii) Connect the aluminium rod in series with a battery, a key as shown in figure.
(iii) Plug the key, the current flows through the rod from Q to P and observe the direction of motion of the rod.
(iv) Reverse the direction of current by reversing the battery connection. Again observe the direction of displacement of aluminium rod.
(v) Restore the original direction of current and change the direction of field vertically downwards by interchanging the two poles of the magnet. Observe the deflection of rod again.
(vi) Place the wire parallel to magnetic field and allow the current to pass through it. Check the deflection of rod again.
Observation :
(i) On plugging the key in step 3, the aluminium rod moves towards left.
(ii) In step 4, rod displaces towards right.
(iii) In step 5, rod moves towards right again.
(iv) In step 6, rod does not move in any direction.
Conclusion :
(i) Magnetic field exerts a force on a current carrying conductor.
(ii) The force exerted on the current carrying conductor depends upon the direction of current and direction of magnetic field acting on it.
(iii) Displacement of the rod or the magnetic force on it is largest when the direction of current is at right angle to the direction of magnetic field.
(iv) When current carrying conductor is placed parallel to the magnetic field, it experiences no force
(b) Direction of force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it is given by Fleming’s left hand rule. Stretch the thumb, forefinger and middle finger of left hand in such a way that they are mutually perpendicular to each other. If the forefinger points in the direction of magnetic field and the middle finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.
