Resistance, Physics


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.


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.


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
Explain, with the help of a circuit diagram, how the thickness of depletion layer in a p-n junction diode alters when it is forward biased. In the following circuits which one of t

a pendulum is timed ,first for 20 swings and then for 50 swings ; time for 20 swings = 17.4 sec and time for 50 sec = 43.2. calculate the average time per swing/

Th e fixed value resistors are those whose resistance are fixed and cannot be changed. The fixed resistors can be further subdivided into following categories. (a)

project of class12,,to demonstrate electrostatics shielding

Define, with the help of diagram, the principle and working of an a.c. Generator. Write the expression for the e.m.f. generated in the coil in terms of its speed of rotation

An electric motor with a load delivers 5.2 hp to its shaft (1 hp = 746 W). Under these conditions, it operates at 82.8 percent efficiency. a. How much current does the motor d

A standing wave is formed on a tightly stretched string.  The distance between a node and an antinode is: w)  1/8 wavelength x)  1/4 wavelength y)  1/2 wavelength

Making an observation nest for ants An observation nest for the study of the life story of ants can simply be made as follows. Make a wooden U from three 30 cm lengths of w

Draw the final image formed by two lenses: An optical imaging system consists of two positive lenses (L1 and L2). L1 has a focal length f 1 = 10 cm, and L2 has a focal length

NEWTON'S FIRST LAW OF MOTION: This law states that "A body at rest will remain at rest and a body moving with uniform velocity will carry on doing so, until acted on by some un