Resistance, Physics

RESISTANCE:

An electric current is a flow of free electrons through a conductor. The size of current flowing through a conductor for a given applied voltage depends on:

• The number of free electrons.
• The opposition to free movement of the electrons caused by the structure of the material.

These two factors taken together give an effective opposition to current flow which is called resistance. To simplify matters it is usual to ignore the second factor and equate good conductors to a large number of free electrons and poor conductors to fewer free electrons. Hence, a good conductor is a material which has low resistance, i.e. a large number of free electrons, and allows a large current to flow. Conversely a poor conductor has a high resistance, i.e. few free electrons and allows only a small current to flow for the same applied voltage. Because the value of the current flowing is determined by the resistance in the circuit, current flow can be controlled by varying the resistance.

Even the best conductors have resistance.

FACTORS AFFECTING RESISTANCE

The four factors that affect the resistance of a wire conductor are:
• Material. Some materials conduct better than others.
• Length ( ). Resistance is directly proportional to length, thus if the length is doubled (other factors remaining constant), resistance is doubled.
• Cross Sectional Area (A). Resistance is inversely proportional to A. Thus if the cross sectional area is doubled, resistance is halved.
• Temperature. Temperature affects the number of free electrons and hence resistance.

UNITS OF RESISTANCE

Resistance is measured in ohms, symbol ω(omega). The resistance of a piece of material is one ohm if a potential difference of one volt applied across it causes a current of one ampere to flow.

Posted Date: 9/13/2012 1:39:05 AM | Location : United States







Related Discussions:- Resistance, Assignment Help, Ask Question on Resistance, Get Answer, Expert's Help, Resistance Discussions

Write discussion on Resistance
Your posts are moderated
Related Questions
It is the phenomenon of emission of electrons from the surface of metals, when light radiations (Electromagnetic radiations) of suitable frequency drop on them. The emitted electro

Two flawlessly conducting spheres are in an evacuated region of space. One is at a potential of 12 volts as well as the other is at a potential of 15 volts. A free electron is rele

What do you understand by rectifier? Illustrate working of half wave and full wave rectifiers with diagrams. Show the expression for its efficiency? Define a transistor and illu

Extrusion: It is a metal working process that makes long lengths of uniform cross sectional area from a metal billet by causing the latter to flow under hydrostatic pressure by a

,adf'';,g.'';fd,g'' fmdlg;lmdf

Atwood's machine A weight-and-pulley system is used to measure the acceleration because of gravity at Earth's surface through measuring the net acceleration of a set of weight

as flux = E.A and flux density is equal to flux/A then why A/A cannot e cancelled ?

The substances which can be stretched to big values of strain are known as elastomers. e.g. elastic tissue of aorta, the main artery carrying blood from the heart.

how to find the gradient of factors with x and y

In the equal distance method of a deflection magnetometer, the deflections produced by two bar magnets are 30 o and 60 o . Determine the ratio of their magnetic moments?