Tag: electric current, potential difference and resistance

Quizzes (6) Questions (109)

Questions Related to electric current, potential difference and resistance

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

There is a current of 40 amperes in a wire of $10^{-16}m^{2}$ area of cross-section. If the number of free electrons per $m^{3}$ is $10^{29}$, then the drift velocity will be:

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

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

  3. $2.0\times 10^{6}m/s$

  4. $25\times 10^{6}m/s$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

If L is the length of wire so velocity is given by $v=\dfrac{L}{t}$

Total number of free electrons in the wire, $Q=nqLA$

Current,

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

$ I=\dfrac{nqLA}{t} $

$ I=nqvA $

$ v=\dfrac{I}{nqA} $

Where, n is the number of electron, $n={{10}^{29}}$

q is the charge of an electron, $q=1.6\times {{10}^{-19\,}}C$

A is area, $A={{10}^{-16}}\,{{m}^{2}}$

I is current, $I=40\,A$

So, drift velocity,

$ v=\dfrac{40}{{{10}^{29}}\times 1.6\times {{10}^{-19}}\times {{10}^{-16}}} $

$ v=25\times {{10}^{6}}\,m/s $

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

A potential difference $V$ is applied to a copper wire of length $l$ and thickness $d$. If $V$ is doubled, the drift velocity:

  1. Is doubled

  2. Is halved

  3. Remain same

  4. Becomes zero
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In the first case, $E= V/l$ so $E$ is directly proportional to $V$ so $E$ will be doubled. Since $V= IR$ so, $E= IR/l$ so Resistance is doubled and $Vd$ is directly proportional to $E$ so $Vd$ is doubled. So in the case, everything is doubled.

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, 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.

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

When a potential difference $V $  is applied across a conductor at a temperature $T,$  the drift velocity of electrons is proportional to

  1. $\sqrt{V}$

  2. $V$

  3. $\sqrt{T}$

  4. $T$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

We know that Drift velocity $v _d = \displaystyle \dfrac{eE}{m} \tau = \dfrac{e}{m} \tau \left ( \dfrac{V}{l} \right ) $ ($\because E = \dfrac{V}{l})$

so for a particular conductor of a particular length the drift velocity will directly depend upon voltage
Hence $v _d \propto V$. option B is correct.