What is ‘current density? Write the vector equation connecting current density j ⇀ with electric field intensity E → for an ohmic conductor.

Current Density ( J → ) Current density is defined as the current flowing through unit correctional area, that is perpendicular to the flow of current. J → = I A Relation between J → & E → J → = σ E → When, J = Current density σ = Electrical conductivity E = Electric field This is also called as vector form of ohm's law.

What is ‘current density? Write the vector equation connecting current density j ⇀ with electric field intensity E → for an ohmic conductor.

Current Density ( J → ) Current density is defined as the current flowing through unit correctional area, that is perpendicular to the flow of current. J → = I A Relation between J → & E → J → = σ E → When, J = Current density σ = Electrical conductivity E = Electric field This is also called as vector form of ohm's law.

Ohm’s law may also be stated by the equation j ⇀ = σ E ⇀ . What do the symbols j ⇀ , σ and E ⇀ stand for? Show that the combination of units on the two sides are identical.

Formula used: ȷ → = σ E → Here, j → = Current density ( j → = I / A ) σ = Electrical conductivity E → = Electric field. S.I. unit of j = A / m 2 S.I. unit of σ = ( − Ωm ) − 1 S.I. unit of E = V / m . then values in Eq, J = σE A m 2 = ( Ωm ) - 1 V m A m 2 = V ⋅ Ω m 2 A m 2 = A m 2

E M B I B E

NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 5 - Electric Resistance and Ohm's Law>QUESTIONS>Q 1

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What is ‘current density? Write the vector equation connecting current density $\overset{⇀}{j}$ with electric field intensity $\vec{E}$ for an ohmic conductor.

Important Questions on Electric Resistance and Ohm's Law

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 5 - Electric Resistance and Ohm's Law>QUESTIONS>Q 2

Obtain an expression showing the relation between the current-density

j

in a current-carrying conductor, the drift velocity

υ_{d}

, the number of free electrons per unit volume

n

and the electronic charge

e .

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 5 - Electric Resistance and Ohm's Law>QUESTIONS>Q 3

The current flowing through a conductor is given by $I = n e A v_{d} .$

Identify each term in the equation.

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 5 - Electric Resistance and Ohm's Law>QUESTIONS>Q 3

The current flowing through a conductor is given by

I = n e A v_{d} .

Obtain an expression for

v_{d}

, if the current flowing through the conductor of length

l

has its ends maintained at a potential difference of

V

volt.

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 5 - Electric Resistance and Ohm's Law>QUESTIONS>Q 4

What is meant by specific resistance (resistivity) of a conductor? Write its unit. Show how the electric resistance of a wire depends on the resistivity of its material, its length and area of cross-section.

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 5 - Electric Resistance and Ohm's Law>QUESTIONS>Q 5

Ohm’s law may also be stated by the equation $\overset{⇀}{j} = σ \overset{⇀}{E}$ . What do the symbols $\overset{⇀}{j}$ , $σ$ and $\overset{⇀}{E}$ stand for? Show that the combination of units on the two sides are identical.

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 5 - Electric Resistance and Ohm's Law>QUESTIONS>Q 6

Define resistivity of a conductor. Explain the variation of resistance with temperature in metallic wire.

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 5 - Electric Resistance and Ohm's Law>QUESTIONS>Q 6

Define resistivity of a conductor. Explain the variation of resistance with temperature in a piece of carbon.

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 5 - Electric Resistance and Ohm's Law>QUESTIONS>Q 7

Write down a simple relationship to show the variation of resistance with temperature. Define temperature coefficient of resistance. In what way the temperature coefficient of carbon is different from that of common conductors?