Question

A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminium rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed. On the basis of your understanding of this phenomenon, answer the following questions: 

1. Why does the rod get displaced on passing current through it?
2. State the rule that determines the direction of the force on the conductor AB.
3. 1. If the U-shaped magnet is held vertically and the aluminium rod is suspended horizontally with its end B towards due north, then on passing current through the rod from B to A as shown, in which direction will the rod be displaced?
   2. Name any two devices that use current carrying conductors and magnetic fields.

OR

Draw the pattern of magnetic field lines produced around a current carrying straight conductor held vertically on a horizontal cardboard. Indicate the direction of the field lines as well as the direction of current flowing through the conductor.

Answer 1

1. When a current carrying conductor is placed in a magnetic field, it experiences a force, due to which the rod gets displaced.
2. The rule that determines the direction of force on the conductor AB is Fleming's left hand rule. The direction of the current and that of the magnetic field are perpendicular to each other and found that the force is perpendicular to both of them. The three directions can be illustrated through a simple rule, called Fleming’s left-hand rule. According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular.
   If the first finger points in the direction of magnetic field and the second finger in the direction of current, then the thumb will point in the direction of motion or force.
   
3. 
   
   1. According to Fleming's left hand rule, the rod will get displaced upwards.
   2. Devices that use current carrying conductors and magnetic field are electric motor, electric generator, loudspeaker, microphones etc.

OR

The magnetic field lines around a current carrying conductor can be represented by concentric circles. The direction of magnetic field can be determined by using right hand thumb rule.