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Multiple choice physics electric current, potential difference and resistance drift velocity and mobility drift speed drift velocity & mobility

The number of free electrons per $10$ mm ordinary copper wire is about $2\times 10^{21}$. The average drift speed of the electrons is $0.25$ mm current flowing is:

  1. $0.8$ A
  2. $8$ A
  3. $80$ A
  4. $5$ A
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given,

Number of electron, $n=2\times {{10}^{21}}$

Average drift speed, $0.25\,mm/s$

$ Q=ne $

$ Q=2\times {{10}^{21}}\times 1.6\times {{10}^{-19}} $

$ Q=320\,C $

Since,

$ s=\dfrac{D}{T} $

$ T=\dfrac{D}{s} $

$ T=\dfrac{10}{0.25}=40 $

So, current

$ I=\dfrac{Q}{T} $

$ I=\dfrac{320}{40} $

$ I=8\,A $

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

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

  1. drift speed

  2. resistivity

  3. resistance

  4. number of free electrons
Reveal answer Fill a bubble to check yourself
D Correct answer
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

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

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} ) $

  1. $ 2.5 \times 10^{-3} $
  2. $ 2.5 \times 10^{-2} $
  3. $ 5 \times 10^{2} $
  4. $ 5 \times 10^{-3} $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Mobility mu = v_d / E. E = V / L = 200 / 2 = 100 V/m. mu = 0.5 / 100 = 0.005 = 5 x 10^-3 m^2/Vs.

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

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

  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 $3.4 \Omega - \mathrm { m }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics electric current, potential difference and resistance drift velocity and mobility drift speed drift velocity & mobility

The mean free path of electrons in a metal is $44 \times 10 ^ { - 8 } \mathrm { m }$ . Theelectric field which can give on an average 2$e \mathrm { V }$ energy to an electron in the metal will be in units of VIm 

  1. $8 \times 10 ^ { 7 }$
  2. $5 \times 10 ^ { - 11 }$
  3. $8 \times 10 ^ { - 11 }$
  4. $5 \times 10 ^ { 7 }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice physics electric current, potential difference and resistance drift velocity and mobility drift speed drift velocity & mobility

When 3 V potential difference is applied a wire of length 0.1 m. having resistivity $1.6 \times 10^{-5}$ $\Omega m$, the electrons started moving. If the electron density in the wire is $6 \times 10^{10} m^{-1}$, the drift speed of electrons is  

  1. $1.94 \times 10^{-6}\ ms^{-1}$
  2. $1.94 \times 10^{-5}\ ms^{-1}$
  3. $1.94 \times 10^{-8}\ ms^{-1}$
  4. $1.94 \times 10^{-7}\ ms^{-1}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics electric current, potential difference and resistance drift velocity and mobility drift speed drift velocity & mobility

The drift velocity of free electron in a metal wire of a given potential gradient along it is $ V _d $ if this potential gradient is doubled the new drift velocity will be 

  1. $ V _d $
  2. $ 2V _d $
  3. $ \frac {V _d}{2} $
  4. $4V _d $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Drift velocity v_d = mu * E. If the potential gradient E is doubled, v_d becomes 2 * v_d.