Tag: electric current

Questions Related to electric current

In conducting wire of radius $5 \, mm$, resistivity $\rho = 1.1 \times 10^{-8} \Omega/m$ and current of $5 A$ is flowing. Drift velocity of free electron is $1.1 \times 10^{-3} \, m/s$ find out mobility of free electron.

physics electric current drift velocity and mobility drift speed drift velocity & mobility

  1. $1.57 \, m^2$ volt/sec

  2. $1.25 \, m^2$ volt/sec

  3. $1.2 \, m^2$ volt/sec

  4. $2 \, m^2$ volt/sec

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Correct Option: A
Explanation:

$V _d = \mu E = \mu \dfrac{V}{\ell}$
$V _d = \dfrac{\mu. I R}{\ell} \dfrac{\mu. I _{\rho} \ell}{A \ell} = \dfrac{\mu . I _{\rho}}{A}$
$\mu = \dfrac{V _d . A}{I _{\rho}} = \dfrac{1.1 \times 10^{-3} \times \lambda \times 25 \times 10^{-6}}{5 \times 1.1 \times 10^{-8}}$
$\mu = 1.57 \,  m^2 $ volt/sec.

A current passes through a resistor. If K$ _1$ and K$ _2$ represent the average kinetic energy of the conduction electrons and the metal ions respectively then

physics electric current drift velocity and mobility drift speed drift velocity & mobility

  1. $K _1 < K _2$

  2. $K _1 = K _2$

  3. $K _1 > K _2$

  4. $\text{Any of these three may occur}$

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Correct Option: C
Explanation:

Considering law of conservation of momentum ,electrons possess drift velocity which is greater than velocity of ions.  Thus $K _1>K _2$. hence correct option is option C.

The drift velocity of the electron in a copper wire of length 2m under the application of a potential difference of 200 V is $0.5 ms^{-1}$.Their mobility is (in $m^{-2} V^{-1} s^{-1}$)

physics electric current drift velocity and mobility drift speed drift velocity & mobility

  1. $5 \times 10^{-3}$

  2. $2.5 \times 10^{-2}$

  3. $5 \times 10^{2}$

  4. $ 10^{-3}$

Show answer
Correct Option: A
Explanation:

Length ,$d=2m$

potential difference ,$V=200V$
Drift velocity, $v _d=0.5 m/s$
mobility ,$\mu=\dfrac{v _d}{E}$
$=\dfrac{v _d .d}{V}$
$=\dfrac{0.5}{200} \times 2$
$=\dfrac{0.5}{100}=5 \times 10^{-3} m^2 V^{-1} s^{-1}$

Find the time an electron takes to drift from one end of a uniform wire $3m$ long to its other end if the wire is $2$ x ${ 10 }^{ -6 }{ m }^{ 2 }$ in cross section and carries a current $3A$.The density of free electrons in a copper conductor is $8.5$ x ${ 10 }^{ 28 }{ m }^{ 3 }$.

physics electric current drift velocity and mobility drift speed drift velocity & mobility

  1. $2.7$ x ${ 10 }^{ 4 }s$

  2. $1.1$ x ${ 10 }^{ -4 }s$

  3. $0.9$ x ${ 10 }^{ -4 }s$

  4. $1.414$ x ${ 10 }^{ 4 }s$

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Correct Option: A

Which of the following quantities do not change when an ohmic resistor connected to a battery is heated due to the current?

physics electric current drift velocity and mobility drift speed drift velocity & mobility

  1. drift speed

  2. resistivity

  3. resistance

  4. number of free electrons

Show answer
Correct Option: D
Explanation:

We know, for a conductor carrying current,
Drift speed $= neI =ne \dfrac{V}{R}$
Resistivity $= \dfrac {RA}{L}$
where,
$n$ is no. of electrons, 
$e$  is charge on electrons,
$V$  is applied voltage,
$R$  is resistance and 
$A$  and $L$  are area of cross-section and length of resistor.
From above equations it is clear that drift speed, resistivityand resistance of resistor will be affected due to heating of resistor

The drift of the electrons in a copper-wire of length 2 m under the application of potential difference of $ 200 V is 0.5 ms^{-1} $ . their mobility is $ (inm^2V^{-1}s^{-1} ) $

physics electric current drift velocity and mobility drift speed drift velocity & mobility

  1. $ 2.5 \times 10^{-3} $

  2. $ 2.5 \times 10^{-2} $

  3. $ 5 \times 10^{2} $

  4. $ 5 \times 10^{-3} $

Show answer
Correct Option: D

In semiconductor the concentrations of electrons and holes are $8 \times 10 ^ { 18 } / \mathrm { m } ^ { 3 }$and $5 \times 10 ^ { 8 } / \mathrm { m } ^ { 3 }$ respectively.If the mobilities of electrons and holes are 2.3$\mathrm { m } ^ { 2 } / \mathrm { Vs }$ and 0.01$\mathrm { m } ^ { 2 } / \mathrm { Vs }$ respectively then semi conductor is

physics electric current drift velocity and mobility drift speed drift velocity & mobility

  1. N-type with resistivity $0.34 \Omega - \mathrm { m }$

  2. P-type with resistivity $0.34 \Omega - \mathrm { m }$

  3. N-type with resistivity $0.034 \Omega - \mathrm { m }$

  4. P-type with resistivity $3.4 \Omega - \mathrm { m }$

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Correct Option: C

Unit of mobility :

physics electric current drift velocity and mobility drift speed drift velocity & mobility

  1. $Cskg$

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

  3. $Cskg^{-1}$

  4. $m^2 V^{-1} s$

Show answer
Correct Option: B
Explanation:

Mobility    $\mu = \dfrac{v _d}{E}$

Unit of  $v _d $ is  $m/s$  and  that of  $E$ is $V/m$
So, its unit is    $m^2 V^{-1}s^{-1}$

A house is fitted with 10 tubes of 40 W. If all tubes are lighted for 10 hours and if the cost of one unit of electricity energy is Rs. 2.50 the total cost of electricity consumption is ...

physics electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. Rs. $100$

  2. Rs. $20$

  3. Rs. $25$

  4. Rs. $10$

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Correct Option: D

The resistance of a hot tungsten filament is about $10$ times the cold resistance. What will be the resistance of $100\ W,\ $$200\ V$ lamp when not in use?

physics electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. $20\Omega$

  2. $40\Omega$

  3. $200 \Omega$

  4. $400 \Omega$

Show answer
Correct Option: B
Explanation:
When the lamp is in use, it is hot.

Using Joule's Law of heating,
$P = \cfrac{V^2}{R}$
$R= \cfrac{200^2}{100}=400\Omega$ when operating 

It is given resistance of hot lamp is 10 times the cold lamp.
Hence, $R _{cold}=\cfrac{400}{10}=40\Omega$