Tag: electric current

Quizzes (8) Questions (16)

Questions Related to electric current

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 drift velocity and mobility drift speed drift velocity & mobility

The drift velocity of the electron in a copper wire of length 2m under the application of a potential difference of 200 V is $0.5 ms^{-1}$.Their mobility is (in $m^{-2} V^{-1} s^{-1}$)

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

  2. $2.5 \times 10^{-2}$

  3. $5 \times 10^{2}$

  4. $ 10^{-3}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Length ,$d=2m$

potential difference ,$V=200V$
Drift velocity, $v _d=0.5 m/s$
mobility ,$\mu=\dfrac{v _d}{E}$
$=\dfrac{v _d .d}{V}$
$=\dfrac{0.5}{200} \times 2$
$=\dfrac{0.5}{100}=5 \times 10^{-3} m^2 V^{-1} s^{-1}$

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

Find the time an electron takes to drift from one end of a uniform wire $3m$ long to its other end if the wire is $2$ x ${ 10 }^{ -6 }{ m }^{ 2 }$ in cross section and carries a current $3A$.The density of free electrons in a copper conductor is $8.5$ x ${ 10 }^{ 28 }{ m }^{ 3 }$.

  1. $2.7$ x ${ 10 }^{ 4 }s$

  2. $1.1$ x ${ 10 }^{ -4 }s$

  3. $0.9$ x ${ 10 }^{ -4 }s$

  4. $1.414$ x ${ 10 }^{ 4 }s$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Time t = length / v_d. First find v_d = I / (neA). With I=3, n=8.5e28, A=2e-6, v_d = 3 / (8.5e28 * 1.6e-19 * 2e-6) = 1.1e-4 m/s. Then t = 3 / 1.1e-4 = 2.7e4 s.

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 thermal effect of electric current heating effect of electric current electric current and its effects

A house is fitted with 10 tubes of 40 W. If all tubes are lighted for 10 hours and if the cost of one unit of electricity energy is Rs. 2.50 the total cost of electricity consumption is ...

  1. Rs. $100$

  2. Rs. $20$

  3. Rs. $25$

  4. Rs. $10$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Total power = 10 tubes * 40 W = 400 W = 0.4 kW. Energy = 0.4 kW * 10 hours = 4 kWh. Cost = 4 kWh * 2.50 Rs/kWh = 10 Rs.

Multiple choice physics electric current thermal effect of electric current heating effect of electric current electric current and its effects

The resistance of a hot tungsten filament is about $10$ times the cold resistance. What will be the resistance of $100\ W,\ $$200\ V$ lamp when not in use?

  1. $20\Omega$

  2. $40\Omega$

  3. $200 \Omega$

  4. $400 \Omega$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
When the lamp is in use, it is hot.

Using Joule's Law of heating,
$P = \cfrac{V^2}{R}$
$R= \cfrac{200^2}{100}=400\Omega$ when operating 

It is given resistance of hot lamp is 10 times the cold lamp.
Hence, $R _{cold}=\cfrac{400}{10}=40\Omega$