Advertisements
Advertisements
प्रश्न
Obtain the macroscopic form of Ohm’s law from its microscopic form and discuss its limitation.
उत्तर
- Consider a segment of wire of length l and area of cross-section A
- Electric field is created when a potential difference V is applied
- If ‘E’ is uniform, then, V = El
- Current density, J = σ E = σ`"V"/l`
Since J = `"I"/"A"`
`"I"/"A" = sigma "V"/l`
Rearranging the above equation, Current through the conductor
Current through the conductor
V = `"I"(l/(sigma"A"))`
Where `(l/(sigma"A"))` → resistance of conductor (R)
∴ R `alpha (l/(sigma"A"))`
∴ The macroscopic form of Ohm's law is
V = IR ...[V α I]
Limitations:
There are certain materials and devices where the proportionality of V and I does not hold good.
APPEARS IN
संबंधित प्रश्न
If the potential difference across the ends of a conductor is 220 V and the resistance of the conductor is 44 Ω (ohm), then the current flowing through is _________.
- 0.2 A
- 0.5 A
- 2 A
- 5 A
What will be the change in the current if the potential difference is kept constant and the resistance of the circuit is made four times?
- It will remain unchanged.
- It will become four times.
- It will become one-fourth.
- It will become half.
A low voltage supply from which one needs high currents must have very low internal resistance. Why?
Name the unit of electrical resistance and give its symbol.
What is the necessary condition for a conductor to obey Ohm’s law?
A wire has a length of 2.0 m and a resistance of 5.0 Ω. Find the electric field existing inside the wire if it carries a current of 10 A.
A metal sphere is kept on an insulting stands. A negatively charged rod is brought near it, then the sphere is earthed as shown. On removing the earthing, and taking the negatively charged rod away, what will be the nature of charge on the sphere? Give reason for your answer.
The unit of specific resistance is ____________.
Suppose there is a circuit consisting of only resistances and batteries and we have to double (or increase it to n-times) all voltages and all resistances. Show that currents are unaltered. Do this for circuit of Example 3.7 in the NCERT Text Book for Class XII.
A current of 3.2 mA flows through a conductor. If charge on an electron is - 1.6 × 10-19 coulomb, find the number of electrons that will pass each second through the cross section of that conductor.
