## Monday, 8 June 2015

### Resistor or Resistance

In electromagnetism, the resistance is the ability of an object to hinder current through to the equation is defined as

R= v/r

Wherein, R is the resistance, V is the voltage across the object, I is the current through the object.
Assuming that the object has a uniform cross-sectional area, the resistance and resistivity, proportional to the length, and inversely proportional to the cross-sectional area.

SI units, the resistance in ohms (Ω, Ohm). Resistance reciprocal conductance in siemens (S).
The temperature is assumed constant, many substances will abide by Ohm's law, objects consisting of these substances, the resistance is constant, not with the current or voltage. These substances referred to as "ohm substance"; failure to comply with Ohm's law matter is "non-ohmic material." R circuit symbol often used to represent, for example: R1, R02, R100 and so on.

Wire like a class of objects, having a low resistance, can be very efficient current transfer, such objects called "conductor." Usually by conductor such as copper, gold and silver-metal manufacturing has excellent conductive properties, or inferior conductive properties of aluminum.

The resistor is a circuit element having a specific resistance. Raw materials used in the preparation of the resistor there are many; what materials should be used, depending on the specified resistance, energy dissipation, and so accurate, and cost factors.

Suppose wire conducting a high frequency alternating current, since the skin effect, the effective cross-sectional area of the wire decreases. Assume several parallel wires together, due to the proximity effect, the effective resistance of each wire will be greater than the resistance of a single wire. For ordinary household AC power, since the frequency is low, the effect is very small, you can ignore these effects.