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Mobility of free electrons in a conductor is

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Important Questions on Current Electricity

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

A current of

10 A

exists in a wire of cross-sectional area of

5 {mm}^{2}

with a drift velocity of

2 \times 10^{- 3} {m s}^{- 1} .

The number of free electrons in each cubic meter of the wire is

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

A charged particle having drift velocity of

7.5 \times 10^{- 4} m s^{- 1}

in an electric field of

3 \times 10^{- 10} V m^{- 1}

, has a mobility in

m^{2} V^{- 1} s^{- 1}

of:

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

An electron of mass

m

and charge

q

is accelerated from rest in electric field

E

. The velocity acquired by the electron in travelling a distance

x

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

A potential difference of

5 V

is applied across a conductor of length

0.1 m

. If the electron mobility is

5 \times 10^{- 6} m^{2} v^{- 1} s^{- 1}

then the drift velocity of electron is

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

The number of free electrons per

100 mm

of ordinary copper wire is

2 \times 10^{21}

. Average drift speed of electrons is

0.25 mm s^{- 1}

. The current flowing is

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

The dimensional formula of mobility is _____

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

A copper wire of

3 {m m}^{2}

cross sectional area carries a current of

5

ampere. The magnitude of the drift velocity for the electrons in the wire, (Assume copper to be monovalent,

M_{C u} = 63.5 k g / k m o l

and density of copper

= 8920 k g m^{- 3}

)

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

Assertion (A): As soon as a source of emf is connected across a conductor, a current immediately starts flowing through it.
Reason (R): Drift speed of the electron is so large that electron travel from one end of the conductor to the other end almost instantaneously.

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

A current of

5 A

passes through a copper conductor (resistivity

= 1.7 \times 10^{- 8} Ω m

) of radius of cross-section

5 m m

. Find the mobility of the charges if their drift velocity is

1.1 \times 10^{- 3} m s^{- 1}

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

Though the electron drift velocity is small and electron charge is very small, a conductor can carry an appreciably large current because

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

Two metal wires of identical dimensions are connected in series. If

v_{1}

and

v_{2}

are the conductivities of the metal wires respectively, the effective conductivity if the combination is:

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

The electrical conductivity of a metal is

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

Column - I gives certain physical terms associated with flow of current through a metallic conductor. Column - II gives some mathematical relations involving electrical quantities. Match Column - I and Column - II with appropriate relations.

Column - I	Column - II
(A) Drift Velocity	$(P) \frac{m}{n e^{2} ρ}$
(B) Electrical Resistivity	$(Q) n e v_{d}$
(C) Relaxation Period	$(R) \frac{e E}{m} τ$
(D) Current Density	$(S) \frac{E}{J}$

HARD

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

Suppose the drift velocity

v_{d}

in a material varied with the applied electric field E as

v_{d} \propto \sqrt{E}

. Then

V - I

graph for a wire made of such a material is best given by:

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

The conductivity of a conductor decreases with temperature because, on heating:

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

Drift speed of electrons, when

1.5 A

current flows in a copper wire of cross section

5 {mm}^{2}

v_{d} .

If the electron density in copper is

9 \times 10^{28} m^{- 3}

the value of

v_{d}

mm s^{- 1}

is close to (Take charge of an electron to be

= 1.6 \times 10^{- 19} C

)

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

Assertion: The drift velocity of electrons in a metallic wire will decrease, if the temperature of the wire is increased.

Reason: On increasing the temperature, conductivity of metallic wire decreases.

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

A steady current flows in a metallic conductor of non-uniform cross section. The quantity/quantities that remains/remain constant along the length of the conductor is/are

EASY

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

A copper wire with a cross-section area of

2 \times 10^{- 6} m^{2}

has a free electron density equal to

5 \times 10^{22} {cm}^{- 3} .

If this wire carries a current of

16 A

, the drift velocity of the electron is

HARD

Physics>Electricity and Magnetism>Current Electricity>Drift of Electrons and the Origin of Resistivity

When

5 V

potential difference is applied across a wire of length

0.1 m

, the drift speed of electrons is

2.5 \times 10^{- 4} m s^{- 1}

. If the electron density in the wire is

8 \times 10^{28} m^{- 3}

, the resistivity of the material is close to:

Mobility of free electrons in a conductor is

Important Questions on Current Electricity

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