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

A charged particle having drift velocity of $7.5\times 10^{-4}m$ $s^{-1}$ in electric field of $3\times 10^{-10}$V $m^{-1}$, mobility is?

  1. $6.5\times 10^6m^2V^{-1}s^{-1}$

  2. $2.5\times 10^6m^2V^{-1}s^{-1}$

  3. $2.5\times 10^4m^2V^{-1}s^{-1}$

  4. $6.5\times 10^4m^2V^{-1}s^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given:
$V _d=7.5 \times 10^{-4}$
$E=3 \times 10^{-10}$
Mobility of charged particle
$\mu =\dfrac{|v _d|}{E}=\dfrac{7.5\times 10^{-4}}{3\times 10^{-10}}=2.5\times 10^6m^2V^{-1}s^{-1}$.

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

Which of the following characteristics of electrons determines the current in a conductor?

  1. Drift velocity alone

  2. Thermal velocity alone

  3. Both drift velocity and thermal velocity

  4. Neither drift nor thermal velocity
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A. Drift velocity only.


The current in a conductor,

$I= neA V _{d}$
    where, $n=$ no. of free charge density
                $A=$ cross-sectional area of conductor
                 $V _{d}=$ Drift velocity
From the above, Drift velocity is only responsible for the current in a conductor.

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

When current flows through a conductor, then the order of drift velocity of electrons will be:-

  1. $10^{10} cms^{-1}$

  2. $10^{-2} cms^{-1}$

  3. $10^{4} cms^{-1}$

  4. $10^{-1} cms^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The drift velocity of electrons in a conductor is of the order of $10^{−4} m/s. It is very small compared to the thermal speed which is of the order of 105 m/s.

The answer is $10^{-2}$

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

Potential difference of $100 V$ is applied to the ends of a copper wire one metre long. Find the ratio of average drift velocity and thermal velocity of electrons at $27^\circ C$. (Consider there is one conduction electron per atom. The density of copper is $9.0 \times 10^3$; Atomic mass of copper is $63.5 g$.
$N _A = 6.0 \times 10^{23}$ per gram-mole, conductivity of copper is $5.81 \times 10^{7} \Omega^{-1}$.$K =1.38 \times 10^{-23} JK^{-1}$).

  1. $3.67 \times 10^{-6}$

  2. $4.3 \times 10^{-6}$

  3. $6 \times 10^{-5}$

  4. $5.6 \times 10^{-6}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Drift velocity is given by v_d = (eE tau) / m, and thermal velocity is v_th = sqrt(3kT / m). Using the provided conductivity and density, the ratio is calculated as approximately 3.67 x 10^-6.

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

Assertion: When a straight wire is bent to form L-shape, its resistance increases.
Reason: Electrons take longer time to travel along a bent wire, as compared to travel along a straight wire.

  1. A

  2. B

  3. C

  4. D
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Resistance is a property of the material and its geometry (length and area). Bending a wire does not change its length or cross-sectional area, so the resistance remains constant. The reason provided is also physically incorrect as drift velocity is determined by the electric field and scattering, not the path geometry.

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

When the current in a wire is 1A, the drift velocity is $1.2\times 10^{-4}ms^{-1}$. The drift velocity when current becomes 5 A is

  1. $1.2\times 10^{-4}ms^{-1}$

  2. $3.6\times 10^{-4}ms^{-1}$

  3. $6\times 10^{-4}ms^{-1}$

  4. $4.8\times 10^{-4}ms^{-1}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given
Initial current through the wire is $I = 1A$
Initial drift velocity is, $v _d = 1.2 \times 10^{-4} ms^{-1}$
Increased current is, $I' = 5A$
The current, I through the wire is given by
$I = \mu _e.e.A.v _d$
where, $\mu _e$ is the free electron density, e is the charge on electron, A is the area of cross section of the wire and v_d is the drift velocity of electrons. 
Since,  the free electron density, the charge on electron and the area of cross section of the wire are constant, hence
$I \propto v _d$.................(1)
Now, current through the wire is increased to 5 A, if the new drift velocity of electrons is $v' _d$ then
$I' \propto v' _d$................(2)


From (1) and (2), we can write

$\dfrac{v' _d}{v _d} = \dfrac{I'}{I}$

$v' _d = \dfrac{I'}{I} v _d$

$v' _d = \dfrac{5}{1} 1.2 \times 10^{-4}$ 

$v' _d = 6 \times 10^{-4} ms^{-1}$ 

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

A charge $A$ of $+3 \ mC$ is placed at $k=0$ and a charge $B$ of $-5 \ mC$ at $k=40 \ mm.$ Where a third charge q be placed on the axis such that it experiences no force is

  1. $1.6 \times 10^{-1} \ m$ from $B$ outside

  2. $2.52 \times 10^{-1} \ m$ from $B$ outside

  3. $4.42 \times 10^{-1} \ m$ from $B$ outside

  4. $8.24 \times 10^{-1} \ m$ from $B$ outside.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For a charge to experience no force, the electric fields from the two charges must cancel out. Since the charges have opposite signs, the null point must be outside the region between them, closer to the smaller magnitude charge (3 mC). Solving k(q1)/x^2 = k(q2)/(x+d)^2 leads to the position 1.6 x 10^-1 m from the -5 mC charge.

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

Mobility of free electrons in a conductor is:

  1. directly proportional to electron density

  2. directly proportional to relaxation time

  3. inversely proportional to electron density

  4. inversely proportional to relaxation time
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Mobility of free electrons, $\mu = \dfrac{q\tau}{m}$        

$\implies$    $\mu \propto \tau$               $(\because q$ and $m$ are constants $)$
Hence mobility of free electrons in a conductor is directly proportional to relaxation time.

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

A 2-ampere current flows in a conductor which has $1 \times {10^{24}}$ free electrons per meter. What is their average drift velocity?

  1. $1.25\,m/s$

  2. $125000\,m/s$

  3. $3 \times {10^8}\,m/s$

  4. $1.25 \times {10^{ - 5}}\,m/s$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

We know 
$I = \eta eAV$
$2 = 1 \times {10^{24}} \times 1.6 \times {10^{ - 24}} \times 1 \times v$
$\boxed{v = 1.25\,m/s}$

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

An electric current of $16A$ exists in a metal wire of cross section ${ 10 }^{ -6 }{ m }^{ 2 }$ and length $1m$. Assuming one free electron per atom. The drift speed of the free electrons in the wire will be:
(Density of metal $=5\times { 10 }^{  }kg/{ m }^{ 3 }$, atomic weight $=60$)

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

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

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

  4. $7.5\times { 10 }^{ -3 }m/s$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

We know,


$I=neAv _d$
      where n=electron density,
                  e=electronic charge
                  A= cross section area
                  $v _d$=drift velocity

But, $n=\dfrac{\rho}{Atm. \ Wt}\times N _A$

And $v _d=\dfrac{I}{neA}$

So, $v _d=\dfrac{16\times 60}{5\times 10^4\times N _A\times 1.6\times 10^{-19}\times 10^{-6}}$

Taking $N _A=6\times 10^{23}$

$v _d=\dfrac{120\times 10^{-2}}{6}=2\times 10^{-3}$