2. Resistance and Resistivity
What is resistance?
◦ It is the opposition to the current flow offered by
the component.
Why do conductors offer resistance?
◦ Due to collision between electrons and vibrating
atoms.
◦ The more the collision, more will be the
resistance offered, and less current will flow at
particular voltage
◦ http://www.absorblearning.com/media/attachmen
t.action?quick=t6&att=2090
◦ Formula:
3. Resistance and Resistivity
Formula:
On what factors does the Resistance
depends?
Which wire will have more resistance?
◦ A)
◦ B)
Rho is the Resistivity of material.
4. Resistance and Resistivity
Does the Resistance depends upon the
temperature of body?
◦ Yes, the Resistance of conductor increases with
increase in temperature.
Why?
◦ What is the relation between the K.E and
Temperature of body?
◦ K.E of atoms is directly proportional to T
◦ So when you increase temperature the atoms
start vibrating with greater amplitude, thus
increasing the chances of more collision.
◦ http://www.absorblearning.com/media/attachmen
t.action?quick=11a&att=2673
5. Resistance and Resistivity
The rho i.e , is called the resistivity of
conductor.
Does it depends on Length and Area like
the “resistance”??
◦ No
◦ It Is the property of certain material.
◦ It is defined as the resistance of 1 meter
cube of substance.
◦ http://phet.colorado.edu/sims/resistance-in-a-
wire/resistance-in-a-wire_en.html
◦ But it do change with change in temperature
like “resistance” of conductor?
6. Resistance and Resistivity
Temperature co-efficient of resistance.
◦ Change in resistance per Kelvin
◦ Formula :
◦ Can have a negative value?
Yes,But what is the meaning of –ve ?
Temperature co-efficient of resistivity.
◦ Change in resistivity per Kelvin
◦ Formula:
7. Resistance and Resistivity
Example 13.2:
◦ 0.75A current flows through an iron wire and
when a battery of 1.5V is connected across
its ends.The length of wire is 5m and its
cross sectional area is 2.5E-7 . .Find the
resistivity?
Example 1:
◦ If the Area is doubled will the resistance
increase or decrease and by what amount?
◦ Does the resistivity increase/decrease by
same amount?
