Tag: charging and discharging

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Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

A capacitor is a perfect insulator for:

  1. constant direct current

  2. alternating current

  3. direct as well as alternating current

  4. variable direct current.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A capacitor consists of two conductors separated by an insulator. In a DC circuit, it blocks current once charged. In an AC circuit, it allows current to flow due to the changing electric field, but it is still physically an insulator between the plates.

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

Four charges $+Q,-Q,+Q$ and $-Q$ are situated at the corners of a square; in a sequence then at the centre of the square:

  1. $E=0,V=0$

  2. $E=0,V\neq 0$

  3. $E\neq 0,V=0$

  4. $E\neq 0,V\neq 0$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Four charges $+Q$, $-Q$, $+Q$, $-Q$.

In this context, $E\neq 0$ but $V=0$ because. $E$ is not cancel out to each other but $V$ is cancel out each other.

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

There are two charges $+2\mu\ C\ and -3\mu\ C$. The ratio of forces acting on them will be 

  1. $2:3$

  2. $1:1$

  3. $3:2$

  4. $4:9$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

There are two charges $+2\mu C$ and $-3\mu C$. The ratio of forces acting on them will be $F=\dfrac { { q } _{ 1 }{ q } _{ 2 }K }{ { r }^{ 2 } } $

$\dfrac { { F } _{ 1 } }{ { F } _{ 2 } } =\dfrac { { q } _{ 2 } }{ { q } _{ 1 } } =\dfrac { 3 }{ 2 } $ or  ${ F } _{ 1 }:{ F } _{ 2 }=3:2$

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

A light beam travelling in the x-direction is described by the electric field ${ E } _{ y }=(300V{ m }^{ -1 })sin\quad \omega (t-x/c).$ An electron is constrained to move along the y-direction with a speed of $2.0\times  {10}^7 { m }^{ -1 }$ Find the maximum electric force and the maximum magnetic force on the electron

  1. $4.8\times {10}^{-17} N, zero$

  2. $4.2\times {10}^{-18} N, 1.8\times 10^{-8}N$

  3. $4.8\times {10}^{-17} N, 3.2\times 10^{-18}N$

  4. Zero, Zero
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
A light beam travelling 
${ E } _{ y }=\left( 300V/m \right) sinw\left( t-x/c \right) $.
$V=2.0\times { 10 }^{ 7 }{ m }^{ -1 }$
${ B } _{ 0 }=\dfrac { { F } _{ 0 } }{ C } =\dfrac { 300 }{ 2\times { 10 }^{ 7 } } =150\times { 10 }^{ -7 }T$
${ F } _{ m }={ B } _{ 0 }qV$
       $=9.1\times { 10 }^{ -31 }\times 150\times { 10 }^{ -7 }\times 2\times { 10 }^{ 7 }$
       $=2.8\times { 10 }^{ -28 }\times 2$
       $=4.8\times { 10 }^{ -17 }N$
magnetic force $=0$
because they are perpendicular to each other.
Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

Two charges Q and -2Q are placed at some distance. the locus of points in the plane of the charges where the potential is zero will be

  1. Straight line

  2. Circle

  3. Parabola

  4. ellipse
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Two charges $Q$, $-2Q$
some distance
Potential $=0$
hence,
$\dfrac { 1 }{ 4\pi { \epsilon  } _{ 0 } } \times \dfrac { Q\times \left( -2Q \right)  }{ R } =0$
When we use it the parabolic condition then,
${ y }^{ 2 }=4ax\quad \longrightarrow \left( 1 \right) $
Now,
$\dfrac { 1 }{ 4\pi { \epsilon  } _{ 0 } } \times \dfrac { Q\times 2Q }{ R } =0$
$\dfrac { { 2Q }^{ 2 } }{ R } =0\quad \longrightarrow \left( 2 \right) $
Hence, equating $(1)$ and $(2)$ and we get, the system is getting parabola.
Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

Force of attraction between two point charges $Q$ and $-Q$ separated by $d$ meter is $F _e$. When these charges are placed two identical sphere of radius $R=0.3\ d$ whose centries are $d$ meter apart the force of attraction between them is 

  1. Greater than $F _{e}$

  2. Equal to $F _{e}$

  3. Less than $F _{e}$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Force of attraction between two point charges $Q$ and $-Q$ separated by $d$.

Force ${ F } _{ e }$
radius $=R=3d$
That is also equal to ${ F } _{ e }$ because the distance is same hence force is also same.

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

Two lithium nuclei in a lithium vapour at room temperature do not combine to form a carbon nucleus- because:

  1. a lithium nucleus is more tightly bound than a carbon nucleus

  2. carbon nucleus is unstable particle

  3. it is not energetically favourable

  4. coulomb repulsion does not allow the nuclei to come very close
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Two lithium nuclei in a lithium vapor can combine only if vapor is heated to a very high temperature. so that the nuclei acquire high kinetic energy to penetrate the coulomb barrier. The vapor is also compressed to a very high pressure.

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

When a negatively charged ebonite rod is brought near a negatively charged and freely suspended ball, then the ball :

  1. gets repelled

  2. attracted

  3. is not affected

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

When two like charges are brought closer, they repel and when two unlike charges are brought closer, they attract each other.
Hence, when a negatively charged ebonite rod is brought near a negatively charged and freely suspended ball, then the ball gets repelled.

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

When a comb is rubbed with hair, it attracts paper bits. Choose the right explanation:

  1. Bits of paper gets attracted due to gravitational force

  2. Due to electromagnetic effect, bits of paper are attracted

  3. Comb gets charged by friction and attracts bits of paper

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When comb is rubbed to hair, it induces negative charge due to friction. When it is brought close to paper bits, they get polarized and the positive part sticks to the comb due to electrostatic attraction.