Tag: drift velocity & mobility

Quizzes (0) Questions (60)

Questions Related to drift velocity & mobility

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 drift velocity and mobility drift speed drift velocity & mobility

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.

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. $K _1 < K _2$

  2. $K _1 = K _2$

  3. $K _1 > K _2$

  4. $\text{Any of these three may occur}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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.