Tag: physics

Questions Related to physics

When there is an electric current through a conducting wire along its length then an electric field must exist

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

  1. inside the wire but normal to it

  2. inside the wire but parallel to it

  3. outside the wire but normal to it

  4. outside the wire but parallel to it

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Correct Option: B
Explanation:

As current is flowing through it , it means charges are flowing along its length therefore heir must be some electric field parallel to the length of the wire. Hence correct option is B.

Copper contains $8.4\times 10^{28}$ free electrons$/m^3$. A copper wire of cross-sectional area $7.4\times 10^{-7}m^2$ carries a current of $1$A. The electron drift speed is approximately.

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

  1. $10^{-8}$m/s

  2. $10^3$m/s

  3. $1$m/s

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

Show answer
Correct Option: D
Explanation:

$v=\dfrac{I}{ne}=\dfrac{1}{7.4\times 10^{-7}}\times 8.4\times 10^{28}$
$=\dfrac{10^{-2}}{8.4\times 1.6\times 7.4}=10^-3$.

Drift velocity varies with the intensity of electric field as per the relation

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

  1. ${v} _{d}\propto E$

  2. ${v} _{d}\propto \cfrac{1}{E}$

  3. ${v} _{d}=$ constant

  4. ${v} _{d}\propto {E}^{2}$

Show answer
Correct Option: A
Explanation:

Current , $I$ = $neAv _{d} $

Current density , $J$ = $\frac{I}{A}$ = $nev _{d} $
Also , current density $J$ is related to electric field $E$
by the relation 
$J = \sigma E$
Therefore , 
$nev _{d}$ = $J = \sigma E$
Hence , $v _{d}  \alpha E$ .

a current 10 ampere is maintained in a conductor of cross section of $ 10^{-4}m^2 $. if the electron density is $ 9 \times 10^{28} m^{-3} $ , what is the drift velocity of free electrons?

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

  1. $ 6.9 \times 10^{-6} ms^{-1} $

  2. $ 6.9 \times 10^{-4} ms^{-1} $

  3. $ 6.9 \times 10^{5} ms^{-1} $

  4. none of thses

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Correct Option: A

The relaxation time $(t)$ is the:

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

  1. Time taken by an electron to drift from one end of a conductor to the other.

  2. Time taken by an electron to travel unit distance through the conductor.

  3. The time between two successive collisions of a free electron with the atoms of the metal.

  4. Time for which a free electron is subjected to the electric field.

Show answer
Correct Option: C
Explanation:

Relaxation time is the average times between two successive collision between the free electrons and the atoms(kernel) of atoms .


It is denoted by $\tau$.

Answer-(C)

The drift velocity of free electrons in a conductor is $v$, when a current. $I$ is flowing in it if both the radius and current are doubled, then drift velocity will be.

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

  1. $V/4$

  2. $V/2$

  3. $2V$

  4. $4V$

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Correct Option: B

Who invented the cyclotron?

physics scientists inventions and inventors in science indian scientist: biography and achievements scientist and their achievements

  1. James Chadwick

  2. James Clerk Maxwell

  3. Michael Faraday

  4. Ernest Orlando Lawrence

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Correct Option: D
Explanation:

The cyclotron was invented by Ernest Orlando Lawrence.

Which year was declared as International Year of Physics. ?

physics scientists inventions and inventors in science indian scientist: biography and achievements scientist and their achievements

  1. $2002$

  2. $2003$

  3. $2005$

  4. $2007$

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Correct Option: C
Explanation:

The year $2005$ was declared as International year of Physics.

In which year did Hahn and Meitner discover the phenomenon of neutron-induced fission of uranium. ?

physics scientists inventions and inventors in science indian scientist: biography and achievements scientist and their achievements

  1. $1938$

  2. $1950$

  3. $1945$

  4. $1928$

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Correct Option: A
Explanation:

Hahn and Meitner discovered the phenomenon of neutron - induced fission of uranium in $1938$.

Lightning was discovered by the

physics scientists inventions and inventors in science indian scientist: biography and achievements scientist and their achievements

  1. Ohm

  2. Thomson

  3. Franklin

  4. Faraday

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Correct Option: C
Explanation:

Lightning was discovered by Franklin.