Right-Hand Thumb Rule: Reading Magnetic Fields

Right hand thumb Rule Electric current Magnetic field Right hand 4.7 Right hand thumb Rule This is a convenient rule for finding out the direction of the magnetic field produced by a current flowing through an electrical conductor. Imagine that you have held the conductor in your right hand in such a way that your thumb points in the direction of the current. Then turn your fingers around the conductor, the direction of the fingers is the direction of the magnetic lines of force (Fig. 4.7). Find Out The right hand thumb rule is called Maxwell’s cork-screw rule. What is the cork-screw rule? Magnetic field produced by current through a circular loop of a conducting wire. We learnt about the magnetic lines of force of a magnetic field produced by a current flowing through a straight conduc tor. What will happen to the magnetic lines of force of the field produced by a current flowing through a loop made by bending the straight wire? A circuit is completed by connecting various components as shown in the figure 4.8. If the current passes through the loop, magnetic lines of force are produced at each point on the loop. As we go away from the wire, the concentric circles representing the magnetic lines of force will become bigger and bigger. Magnetic lines P Cardboard I N S Conductor loop Q R A + + As we go towards the centre of the loop the circle become so big that its arc can be shown as a straight line. 4.8 Magnetic field produced by a current through a loop of conducting wire In fig. 4.8, the magnetic lines of force are shown near the points P and Q only, however, they will be created near each point on the loop. Likewise, each point will produce magnetic field at the centre of the loop. By making use of the right hand thumb rule, check that every point on the loop contributes the magnetic lines of force at the centre of the loop and these lines of force at the centre of the loop are in the same direction. 53 The intensity of magnetic field at any point produced by a current flowing through a wire, is dependent on the current, as we have seen in the experiment (fig 4.6 Try this). This means that if there are n turns in the loop, the magnetic field n times of that produced by a single loop will be created. On discussing with your teachers, with their guidance, see if you can perform the above experiment by collecting appropriate materials. The direction of the magnetic field can be determined with the help of a magnetic needle