Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area 2.5 × 10 − 7 m 2 carrying a current of 2 . 7 A . Assume the density of conduction electrons to be 9 × 10 28 m − 3 .

Given that, Cross-sectional area, A = 2.5 × 10 − 7 m 2 Amount of current, I = 2.7 A v d = I e n A = 2.7 1.6 × 10 − 19 × 9 × 10 28 × 2.5 × 10 − 7 m s − 1 v d = 0.75 × 10 − 3 m s − 1 = 0.75 mm s − 1 .

When 5 V potential difference is speed across a wire of length 0 . 1 m , the drift speed of electrons is 2.5 × 10 − 4 m / s . If the electron density in the wire is 8 × 10 28 m − 3 , calculate the resistivity of the material of wire.

Given that, Potential difference across wire is 5 V . Length of the wire is 0 . 1 m , Drift speed of electrons is 2.5 × 10 − 4 m / s Electron density is 8 × 10 28 m − 3 Expression for resistance of the wire is R = ρ l A Amount of current in terms of drift velocity is I = enA v d Potential difference across wire is ∴ V = R I = ρ l A ⋅ e n A v d or ρ = V e n v d l ρ = 5 1.6 × 10 − 19 × 8 × 10 28 × 2.5 × 10 − 4 × 0.1 ρ = 1.56 × 10 − 5 Ωm .

A 10 C of charge flows through a wire in 5 minutes. The radius of the wire is 1 mm . It contains 5 × 10 22 electrons per centimetre 3 . Calculate the current and drift velocity.

Given that, Charge flow through a wire is 10 C and the radius of the wire is 1 mm Number of electrons per cm 3 , n = 5 × 10 22 Expression of current is I = q t Or I = 10 C 5 × 60 s = 3.33 × 10 − 2 A Expression for drift velocity is v d = I e n A = I e n π r 2 v d = 3.33 × 10 − 2 16 × 10 − 19 × 5 × 10 2 2 × 10 6 × 314 × 10 − 3 2 v d = 1.326 × 10 − 6 m s − 1

EASY

12th CBSE

IMPORTANT

Earn 100

The free electrons of a copper wire of cross-sectional area $10^{- 6} m^{2}$ acquire a drift velocity of $10^{- 4} m / s$ when a certain potential difference is applied across the wire. Find the current flowing in the wire if the density of free electrons in copper is $8.5 \times 10^{28} electrons / m^{3}$ .

Important Questions on Current Electricity

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 2

Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area

2.5 \times 10^{- 7} m^{2}

carrying a current of

2.7 A

. Assume the density of conduction electrons to be

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

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 3

A current of

1.8 A

flows through a wire of cross-sectional area

0.5 {mm}^{2}

, find the current density in the wire. If the number density of conduction electrons in the wire is

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

. Find the drift speed of electrons.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 4

When

5 V

potential difference is speed across a wire of length

0.1 m

, the drift speed of electrons is

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

. If the electron density in the wire is

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

, calculate the resistivity of the material of wire.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 5

A copper wire of diameter

1.0 mm

carries a current of

0.2 A

. Copper has

8.4 \times 10^{28}

atoms per cubic metre. Find the drift velocity of electrons, assuming that one charge carrier of

1.6 \times 10^{- 19} C

is associated with each atom of the metal.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 6

A current of

2 A

is flowing through a wire of length

4 m

and cross-sectional area

1 {mm}^{2}

. If each cubic metre of the wire contains

10^{29}

free electrons, find the average time taken by an electron to cross the length of the wire.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 7

10 C

of charge flows through a wire in

5

minutes. The radius of the wire is

1 mm

. It contains

5 \times 10^{22}

electrons per

{centimetre}^{3}

. Calculate the current and drift velocity.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 8

A copper wire of diameter

0.16 cm

is connected in series to an aluminium wire of diameter

0.25 cm

. A current of

10 A

is passed through them. Find current density in the copper wire. The number of free electrons per unit volume of aluminium wire is

10^{29} m^{- 3}

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 8

A copper wire of diameter

0.16 cm

is connected in series to an aluminium wire of diameter

0.25 cm

. A current of

10 A

is passed through them. Find drift velocity of free electrons in the aluminium wire. The number of free electrons per unit volume of aluminium wire is

10^{29} m^{- 3}

The free electrons of a copper wire of cross-sectional area 10−6m2 acquire a drift velocity of 10−4m/s when a certain potential difference is applied across the wire. Find the current flowing in the wire if the density of free electrons in copper is 8.5×1028 electrons/m3.

Important Questions on Current Electricity

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