Deduce the relation J → = σ E → from first principles considering Ohm's law to be true.

From Ohm's law-Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. I = V R J = I A = V R A = E I ρ L A A = E ρ = σ E Current density J is a vector quantity which is defined as the current flowing per unit area measured in a direction normal to the direction of flow of charge. The vector J is parallel to the electric field vector.

Show that current density J → = n e 2 τ m E → ?

electrons move with an average velocity which is independent of time, although electrons are accelerated. This is the phenomenon of drift and the velocity v d is called the drift velocity. v d = e E m τ i ∆ t = n e A v d ∆ t i = n e 2 E A m τ j → = i A = c u r r e n t d e n s i t y J → = n e 2 E m τ where ; j =current density A = Area of cross-sectional m =mass of electron e =electron E = electric field τ = Relation time

E M B I B E

Bureau's Higher Secondary Physics Class 12>Chapter 5 - Electric Current>MODEL QUESTIONS>Q 1

HARD

12th Odisha Board

IMPORTANT

Earn 100

Explain the meaning of the drift velocity of electrons. Find an expression for current in conductor in terms of it

Important Questions on Electric Current

HARD

12th Odisha Board

IMPORTANT

Bureau's Higher Secondary Physics Class 12>Chapter 5 - Electric Current>MODEL QUESTIONS>Q 2

State and explain Ohm's law. Deduce it mathematically. Distinguish between ohmic and non ohmic resistance .

MEDIUM

12th Odisha Board

IMPORTANT

Bureau's Higher Secondary Physics Class 12>Chapter 5 - Electric Current>MODEL QUESTIONS>Q 3

Deduce the relation

\vec{J} = σ \vec{E}

from first principles considering Ohm's law to be true.

HARD

12th Odisha Board

IMPORTANT

Bureau's Higher Secondary Physics Class 12>Chapter 5 - Electric Current>MODEL QUESTIONS>Q 4

Discuss the different factors on which the resistance of a conductor depends. How does a semiconductor differ from a conductor?

MEDIUM

12th Odisha Board

IMPORTANT

Bureau's Higher Secondary Physics Class 12>Chapter 5 - Electric Current>MODEL QUESTIONS>Q 5

Show that current density

\vec{J} = \frac{n e^{2} τ}{m} \vec{E}

?

HARD

12th Odisha Board

IMPORTANT

Bureau's Higher Secondary Physics Class 12>Chapter 5 - Electric Current>MODEL QUESTIONS>Q 6

Discuss the variation of resistivity with temperature. Mention two important applications of the phenomenon.

EASY

12th Odisha Board

IMPORTANT

Bureau's Higher Secondary Physics Class 12>Chapter 5 - Electric Current>MODEL QUESTIONS>Q 1

Find the number of electrons that pass through a lamp in one hour if a steady current of $0.5 A$ is maintained in it during the time.

MEDIUM

12th Odisha Board

IMPORTANT

Bureau's Higher Secondary Physics Class 12>Chapter 5 - Electric Current>MODEL QUESTIONS>Q 2

A $12.5 V$ battery operates a $14.2 Ω$ flash light intermittently for a cumulative time of $65.3$ minutes. Calculate the average current and the quantity of electricity furnished by the battery.

MEDIUM

12th Odisha Board

IMPORTANT

Bureau's Higher Secondary Physics Class 12>Chapter 5 - Electric Current>MODEL QUESTIONS>Q 3

Find the number of free electrons in a copper wire of length $1 m$ and cross sectional area $1 {mm}^{2}$ . Determine the charge carried by these free electrons. Number density of free electrons in copper is $8.5 \times 10^{28}$ per $m^{3}$ .

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