What are Dielectrics

  • A dielectric is an insulating material in which all nuclei are tightly bound to the nuclei of the atom.
  • There are no free electrons in a dielectric material so they can not carry current.
  • Electric conductivity of a dielectric material is very low and that of an ideal dielectric is zero.
  • Some examples of dielectric materials are glass, plastic, mica, oil etc.
  • Dielectric constant of a material is the ratio of the capacitance of the capacitor completely filled with the material to the capacitance of the same capacitor in the vacuum i.e. dielectric constant K=C/C0.
  • If the space between a capacitor is filled with a dielectric material capacitance of the capacitor increases.
  • The value of dielectric constant K is independent of the shape and size of the capacitor and its value is different for different insulating materials.

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Problem solving tricks-Right hand rules (Magnetic fields due to currents)

Right hand rule for cross product:-
Consider that c is the cross product of two vectors a and b i.e.,
c=a x b
If direction of vector a is along the x axis and that of b along z axis then direction of vector c could be find using right hand rule for cross products. With the thumb, index, and middle fingers at right angles to each other the first (index) finger can represent a, the first vector in the product; the second (middle) finger, b, the second vector; and the thumb, c, the product. So direction of vector c is perpendicular to the plane containing vectors a and b. This rule can be used in determining the directions of torque and angular momentum vectors and also to find the direction of the force on current carrying wire in an magnetic field.


Right hand thumb rule:-
This rule is used in situations when rotation is specified by a vector and we need to relate a curled element and a straight element , many such situations arises when you study magnetism. This can be done when you curl your fingers and straighten the thumb of your right hand. As an example you can consider an electric current passes through a straight wire. Here, the thumb points in the direction of the conventional current (from positive to negative), and the fingers point in the direction of the magnetic lines of flux.



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