Tag: electric current, potential difference and resistance

Questions Related to electric current, potential difference and resistance

 If 'n' electrons flow through a cross-section of a conductor in time t and charge on an electron is 'e', then the current in the conductor would be :

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. $\displaystyle \frac{ne}{t}$

  2. $\displaystyle \frac{ne^2}{t}$

  3. $\displaystyle \frac{e}{t}$

  4. $\displaystyle \frac{n}{et}$

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Correct Option: A
Explanation:

Consider a conductor of length of $L$ and cross sectional area $A$. 

When an electric field $E$ is applied across it, the electrons are drifted opposite to the applied field. 
Volume of a conductor $= LA =1$ in this case. 
Let $n$ be the number of free electrons per unit volume of conductor.
Total charge on all the electrons in the conductor $= nLAe$ 
where, $e$ is the charge of each electron.

$\Rightarrow  q = nLAe = neAL$ 

But current, $I=\dfrac { q }{ t } =\dfrac { neAL }{ t } =\dfrac { ne }{ t } \quad as\quad AL=1$

Sulphate ions move toward

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. copper electrode

  2. battery

  3. electrolyte

  4. zinc electrode

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Correct Option: D
Explanation:

Sulphate ions move toward zinc electrode.
Oxidation half reaction occurs at anode.
$\displaystyle Zn \rightarrow Zn^{2+} +2e^-$
Positively charged Zn(II) ions enter anode solution. To maintain electrical neutrality, sulphate ions move toward zinc electrode.

In a cell, by convention, charge is taken to be flowing from :

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. positive electrode to negative electrode

  2. negative electrode to positive electrode

  3. both A and B

  4. none of the above

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Correct Option: A
Explanation:

Conventionally, movement (flow) of positive charge is considered and because, unlike charge repel each other, positive charge moves from positive electrode to negative electrode inside the cell. Hence option A is correct.

Two conductors $A$ and $B$ are joined by a copper wire.  If $A$ is positively charged and $B$ is uncharged, the direction of flow of electrons is 

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. $B$ to $A$

  2. $A$ to $B$

  3. no flow

  4. none of these.

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Correct Option: A
Explanation:

The current in the wire is due to the drifting of electrons inside a wire in a direction opposite to the flow of electrons. During their drifting they collide with their atoms vibrating about their mean position and lose some of kinetic energy to the vibrating atoms. The electrons are negatively charged particles and so, the electrons move towards the positively charged conductor A.
Hence, the direction of the flow of electrons in the copper wire is from B to A.

The chemical reaction due to passage of electric current depends on:

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. electrodes.

  2. magnitude of current.

  3. density of liquid.

  4. all of the above.

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Correct Option: A
Explanation:

The chemical reaction due to passage of electric current depends on electrodes.
For example, during electrolysis of aqueous copper sulphate solution using platinum electrodes will give oxygen gas at anode.
On the other hand, during electrolysis of aqueous copper sulphate solution using copper electrodes will oxide Cu to Cu(II) ions at anode.

Conventionally, the direction of the current is taken as

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. the direction of flow to negative charge

  2. the direction of flow of atoms

  3. the direction of flow of molecules

  4. the direction of flow of positive charge

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Correct Option: D
Explanation:

Conventionally the direction of flow of current is taken to be the direction of flow of positive charges.


In wire, electrons possessing negative charges flow and positive charged kernel are at rest.
And, hence the direction of flow of current is opposite to the direction of flow of electrons in wires.

Answer-(D)

It is possible to measure the passage of $50$ electrons per second with a certain sensitive device. This corresponds to a current of :

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. $8 \times 10^{-18} A$

  2. $1.6 \times 10^{-20} A$

  3. $8 \times 10^{-20} A$

  4. $1.6 \times 10^{-19} A$

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Correct Option: A
Explanation:


Let number of electrons per second be n.
Given,
$e = 1.6 \times 10^{-19} C$ ,  $n =50 $
The current is defined as rate of flow of charge,
$I = \dfrac{q}{t} $ 
Hence,
$I = n \times e $

Substituting values,
$I = 50 \times 1.6\times 10^{-19} = 8 \times 10^{-18} A $

Conventionally, the direction of the current is taken as the direction of flow

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. to negative charge

  2. the direction of flow of atoms

  3. of molecules

  4. of positive charge

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Correct Option: D
Explanation:

Conventional Current assumes that current flows out of the positive terminal, through the circuit and goes into the negative terminal of the source.

it's not absolute direction of current it is just conventional which is used to describe the direction of current in electrical circuits.

A particle of mass $2\ g$ and charge $1\ \mu C$ is held at a distance of $1\ m$ from a fixed charge of $1\ mC.$ If the particle of released it will be repelled. Speed  of the particle when it is at a distance of $10\ m$ from the fixed charge is

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. $100\ m/s$

  2. $90\ m/s$

  3. $60\ m/s$

  4. $45\ m/s$

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Correct Option: B
Explanation:

energy of the whole system will be conserved .


so the change in the potential energy of the system will be converted into the kinetic energy of the particle 

$K(q _{1}*q _{2})/(1/r _{1}-1/r _{2})$  $=$  $(m*v^{2})/2$


substituting the values will give 

$V = 90$ $m/s$

On a bulb is written 220 volt and 60 watt. Find out the resistance of the bulb and the value of the current flowing through it:

physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

  1. $806.66 ohm\ and\ 0.27 ampere$

  2. $500 ohm \ and\ 2 amphere$

  3. $200 ohm  \ and\ 4 ampere$

  4. $100 ohm \ and\ 1 ampere$

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Correct Option: A
Explanation:

$R=\dfrac {V^2}{P}=\dfrac {(60^2)}{220}$
$=806.66 \Omega$
$I=\dfrac {P}{V}$
$=\dfrac {6-0}{220}=0.27$