Tag: physics

Questions Related to physics

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:

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

  1. $0.8$ A

  2. $8$ A

  3. $80$ A

  4. $5$ A

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Correct Option: B
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 $

There is current of 40 amperes in a wire of $10^{-6}m^{2}$ area of cross -section. If the number of free electrons per $m^{3}$ is $10^{29}$, then the drift velocity will be 

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

  1. $1.25\times 10^{3}m/s$

  2. $2.50\times 10^{-3}m/s$

  3. $25.0\times 10^{-3}m/s$

  4. $250\times 10^{-3}m/s$

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Correct Option: A

Drift speed of conduction electrons in the wire is

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

  1. $5.5cm/s$

  2. $0.55 mm/s$

  3. $0.22 mm/s$

  4. $1.1 mm/s$

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Correct Option: B

In a wire of cross section radius r, free electrons travel with drift velocity V when a current a $I$ flows throught the wire. What is the current in another wire of half the radius and of the same material when the drift velocity is $2V$ ?

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

  1. $2I$

  2. $I$

  3. $I/2$

  4. $I/4$

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Correct Option: B

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

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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} $

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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

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 

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

  1. $8 \times 10 ^ { 7 }$

  2. $5 \times 10 ^ { - 11 }$

  3. $8 \times 10 ^ { - 11 }$

  4. $5 \times 10 ^ { 7 }$

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Correct Option: D

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  

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

  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. $1.94 \times 10^{-7}\ ms^{-1}$

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Correct Option: C

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 

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

  1. $ V _d $

  2. $ 2V _d $

  3. $ \frac {V _d}{2} $

  4. $4V _d $

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Correct Option: B