What is the drift velocity of electrons in the silver wire of length 1 m , having cross-sectional area 3.14 × 10 − 6 m 2 and carrying a current of 10 A ? Given atomic mass = 108 , density of silver 10.5 × 10 3 kg m − 3 , charge on electron = 1.6 × 10 − 19 C and Avogadro’s number = 6.023 × 10 26 per kg-atom.

Given that, Silver wire of length, l = 1 m , cross-sectional area A = 3.14 × 10 − 6 m 2 Amount of current flowing through wire is 10 A Mass of silver wire, m = A × l × ρ = 3.14 × 10 − 16 × 1 × 10.5 × 10 3 No. of electrons per unit volume of silver, n = 6.023 × 10 23 108 × 3.14 × 10.5 × 10 − 3 3.14 × 10 − 6 × 1 n = 5.8557 × 10 28 Expression for drift velocity is v d = I e × n × A where I is current and A is cross sectional area. v d = 10 1.6 × 10 − 19 × 5.8557 × 10 28 × 3.14 × 10 − 6 v d = 3.399 × 10 − 4 m s − 1 .

A platinum wire has a resistance of 10 Ω at 0 ° C and of 20 Ω at 273 ° C . Find its temperature coefficient of resistance.

Expression for coefficient of resistance is α = R t − R 0 R 0 × t α = 20 − 10 10 × 273 = 1 273 ° C − 1

MEDIUM

12th CBSE

IMPORTANT

Earn 100

A current of $30$ ampere is flowing through a wire of cross‐sectional area $2 {mm}^{2}$ . Calculate the drift velocity of electrons. Assuming the temperature of the wire to be $27 ° C$ , also calculate the $r m s$ velocity at this temperature. Which velocity is larger? Given that Boltzmann’s constant $= 1.38 \times 10^{- 23} {JK}^{- 1}$ , density of copper $8.9 g {cm}^{- 3}$ , atomic mass of copper $= 63$ .

Important Questions on Current Electricity

MEDIUM

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 10

What is the drift velocity of electrons in the silver wire of length

1 m

, having cross-sectional area

r m s

and carrying a current of

10 A

? Given atomic mass

= 108

, density of silver

10.5 \times 10^{3} kg m^{- 3}

, charge on electron

= 1.6 \times 10^{- 19} C

and Avogadro’s number

= 6.023 \times 10^{26}

per kg-atom.

MEDIUM

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 11

When a potential difference of

1.5 V

is applied across a wire of length

0.2 m

and area of cross-section

0.3 {mm}^{2}

, a current of

2.4 A

flows through the wire. If the number density of free electrons in the wire is

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

, calculate the average relaxation time. Given that mass of electron

= 9.1 \times 10^{- 31} kg

and charge on electron

= 1.6 \times 10^{- 19} C

EASY

12th CBSE

IMPORTANT

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

A potential difference of

4.5 V

is applied across a conductor of length

0.1 m

. If the drift velocity of electrons is

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

, find the electron mobility.

EASY

12th CBSE

IMPORTANT

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

The number density of electrons in copper is

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

A current of

1 A

flows through a copper wire of length

0.24 m

and area of cross-section

1.2 {mm}^{2}

, when connected to a battery of

3 V

. Find the electron mobility.

EASY

12th CBSE

IMPORTANT

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

Mobilities of electrons and holes in a sample of intrinsic germanium at room temperature are

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

and

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

respectively. If the electron and hole densities are equal to

3.6 \times 10^{19} m^{- 3}

calculate the germanium conductivity.

EASY

12th CBSE

IMPORTANT

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

A platinum wire has a resistance of

10 Ω

0 ° C

and of

20 Ω

273 ° C

. Find its temperature coefficient of resistance.

EASY

12th CBSE

IMPORTANT

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

The resistances of iron and copper wires at

20 ° C

are

3.9 Ω

and

4.1 Ω

respectively. At what temperature will the resistances be equal? Temperature coefficient of resistivity for iron is

5.0 \times 10^{- 3} K^{- 1}

and for copper it is

4.0 \times 10^{- 3} K^{- 1}

. Neglect any thermal expansion.

EASY

12th CBSE

IMPORTANT

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

The resistance of a silver wire at

0 ° C

1.25 Ω

. Up to what temperature it must be heated so that its resistance is doubled? The temperature coefficient of resistance of silver is

{0.00375}^{\circ} C^{- 1}

. Will the temperature be same for all silver conductors of all shapes?

Important Questions on Current Electricity

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