Resistance
Resistance
As the electrons move through the thin metal filament of the lamp, they encounter more opposition to motion than they typically would in a thick piece of wire. This opposition to electric current depends on the type of material, its cross-sectional area, and its temperature. It is technically known as resistance.
It is that property of a conductor by virtue of which it opposes/resists the flow of charges through it. The SI unit of resistance is ohm, it is represented by the Greek letter
Resistance is the obstruction offered to the flow of electric current. (It can be said that conductors have low resistance and insulators have very high resistance) This resistance serves to limit the amount of current through the circuit with a given amount of voltage supplied by the battery, as compared with the short circuit where we had nothing but a wire joining one end of the voltage source (battery) to the other.
The S.I. unit of resistance is ohm
The reciprocal of resistance is called conductance G= 1/R
Its S.I. unit is or mho or siemen (s).
Some Important Terms Related to Resistance:
Resistor: The component which the offers resistance to the flow of electrons in an electric circuit is known as resistor. Resistors are used to make those electrical devices, where high resistance is required. It reduces current in a circuit, e.g. alloys like nichrome, manganin and constantan.
Rheostat or Variable resistance It is a variable resistor,which is used to control the flow of electric current by manually increasing or decreasing the resistance
Good conductor A material which offers less resistance to the flow of electrons or electric current in an electric circuit is known as a good conductor, e silver, copper, aluminium are good conductors, among these, silver is the best conductor of electricity.
Poor conductor A material which offers higher resistance to the flow of electrons or electric current in an electric circuit is known as poor conductor, e.g. mercury, lead, stainless steel, alloys of iron and chromium are poor conductors.
A certain pieace of silver of given mass is to be made like a wire. Which of the following combination of length (L) and the area of cross - sectional (A) will lead to the smallest resistance - | |||
| Right Option : C | |||
| View Explanation | |||
An electric iron draws a current 4 A when connected to a 220V mains. Its resistance must be | |||
| Right Option : B | |||
| View Explanation | |||
Masses of 3 wires of same metal are in the ratio 1:2:3: and their lengths are in the ratio 3:2:1 The electrical resistances are in ratio- | |||
| Right Option : D | |||
| View Explanation | |||
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