Question

1) Define the unit of resistance.
2) On what factors does the resistance of a conductor depend ?
3) How does the resistance of a conductor change with temperature?
4) Classify materials depending upon the value of resistivity.​

Answer 1

Solution 1 :-

1) the unit of resistance (R) is ohm . it states that if the physical condition like temperature etc. of a conductor are kept unchanged the strength of current flowing through it is directly proportional to the potential difference across it's end .this statement is ohm law.

now fundamental relation

• if V = potential difference applied across the ends of a conductor AB
• I = strength of current flowing through the conductors then according to ohms law
• V = RI
• v stands for potential difference, R is resistance and I is the current

Solution 2 :-

1) resistance of a conductor depends upon :

• it's length (l)
• if the length of the conductor increases, the electrons have to travel longer distance and as a result of this, it's resistance increases . thus R(resistance) is proportional to L (length)
• it's cross -sectional area (A)
• if the cross sectional area of the conductor decreases, the electrons find it more difficult to pass through it and as such it's resistance increases. thus, R (resistance) is inversely proportional to A (cross sectional area)
• resistivity of its material
• resistivity of the material depends on the nature of the material of the conductor and also an temperature .where R is proportional to resistivity

Solution 3 :-

the resistance of a conductor changes with temperature :-

• when a potential difference is applied across the ends of a conductor, these electrons begins to move from lower potential to higher potential.
• the motion of these electrons is not smooth because they experience a resistance on account of their collision with other electrons. as a result of this , some work is done to overcome resistance. it is this work done that is converted into heat
• so with increase in temperature, the resistance of wire increases as collision between the wire increases and it makes the flow of electrons slow
• thus resistance of a conductor changes with temperature.

solution 4 :-

classification of materials on the basis of resistivity

• conductors :- metals like copper, aluminum, silver etc have a very large numbers of free electrons and as such possess small resistivity which increases with temperature and allow the current to move freely are called conductors
• examples of conductors are metals and alloys
• semiconductors :- these possess a few free electrons and as such possess greater resistivity as compared to conductors. the resistivity of semi conductors decreases with temperature .
• examples of semi conductors are silicon, germanium etc
• insulators :- these have practically no free electrons and as such have a very high resistivity which decreases with the rise in temperature
• examples of insulators :- mica, rubber, glass etc.
• super conductors :- these are materials whose resistivity becomes zero below a certain temperature called critical temperature.
• examples of super conductors are magnesium diboride , aluminum etc.

Answer 2

Answer 1)

The resistance of a conductor is said to be one ohm if a current of one ampere flows through it when a potential difference of one volt is applied across its ends.

Answer 2)

Resistance Depends Upon

1. Length Of The Conductor
2. Area Of Cross-section
3. Material or Nature Of Conductor
4. Temperature Of Conductor

Answer 3)

Temperature of the wire: A higher temperature of the wire causes the ions in it to vibrate more rapidly. Therefore, the number of collisions increases, and hence, the resistance increases.

Answer 4)

• Conductors:-Low Resistivity means high conductance, metals like copper, silver have large number of free electrons which possess Small Resistivity which increases on increase in temperature which permits the current to move freely are called conductors.

• Insulators:-High Resistivity means low conductance, these have less or no free electrons which results in great resistivity which low down on rise of temperature

• Semiconductors:- It is very low for metals alloys which makes it low for semiconductor but very high for insulator. The Resistivity decreases with temperature

• Superconductors:- A superconductor is a substance of zero resistance (or infinite conductance) at a very low temperature

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