Resistor, Conductor,Insulator, Capacitor & Inductor

Resistor:
Resistance is one of the three passive elements of electric circuits. Every element has some amount of resistance. The resistance of leads capacitors and inductors can usually be ignored.

From circuit point of view a resistor is a device which shows a constant relation between the voltage drop across it and the current flowing through it. Thus it obeys ohm's law. 
From the energy view point the resistance parameter can be thought of as a device capable of converting electrical energy into heat energy. The resistance parameter is a geometric constant as seen in equation below.

Here, 
 R= resistance (ohms,Ω)
 l  = Length (m)
 A = Area of cross section (m²)        




 Resistors of values ringing from milli-ohm are used in a variety of circuits of electrical machines, instruments,electronics and heating devices. They are classified into wire wound and carbon composition resistors.

Conductor:

Capacitor:

A capacitor is a device capable of strong electric charge. It is one of three passive elements of electric circuits. It consist of two insulated parallel metallic plates with air or any other insulating material in between.

Above Fig. shows two conductive parallel plates separated by an air space and connected to a battery/source. It consists of two insulated parallel metallic plates with air or any other insulating materials in between.

• Electrons flow from the negative terminal of battery to the bottom plate A. Since air is an insulator, these electrons can't go further. They accumulate on the plate A giving it a negative charge.
• The negative charge on plate A produces an electrostatic field around it. The direction of this field is to repel electrons towards plate B.
• Electrons flows from plate B to the positive terminals of the battery. This happens due to the attracting force of the positive terminal and the repelling force of the field due to charge on plate A. Plate B acquires positive charge.
• When plates A and B become charged, negatively and positively respectively, a potential difference build up between them. This difference is in opposition to the battery voltage. When this potential difference becomes equal to applied voltage, no more electrons can flow and the circuit reaches static state.
• When the switch is kept closed or opened does not make any difference. Even if the switch is opened, the potential difference between the plates will be maintained. The capacitor has stored the charge. If the switch is opened and the plates short circuited, the surplus electrons on plate A travel to the plate B. This continues till the potentials of the  two plates become equal and the capacitor becomes completely discharged.