Tag: electric fields

Questions Related to electric fields

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

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

  1. $2:3$

  2. $1:1$

  3. $3:2$

  4. $4:9$

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Correct Option: C
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  ${ F } _{ 1 }:{ F } _{ 2 }=3:2$

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

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

  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

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Correct Option: A
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.

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

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

  1. Straight line

  2. Circle

  3. Parabola

  4. ellipse

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Correct Option: C
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.

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 

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

  1. Greater than $F _{e}$

  2. Equal to $F _{e}$

  3. Less than $F _{e}$

  4. None of these

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Correct Option: B
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.

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

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

  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

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Correct Option: D
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.

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

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

  1. gets repelled

  2. attracted

  3. is not affected

  4. none of these

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Correct Option: A
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.

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

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

  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

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Correct Option: C
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. 

In the thunderstorm, the charges accumulate near the upper edges of clouds are

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

  1. negatively charged

  2. positively charged

  3. neutral

  4. none of these

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Correct Option: B
Explanation:

We have to find the nature of charges on upper edges of clouds in a thunderstorm, the air currents move upwards while the water droplets move downward. This vigorous movement causes separation of charges. This leads to the positive charges collected near the upper edges of clouds and the negative charges to accumulate near the lower edges of the clouds.

The safety fuse should have

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

  1. high resistance and high melting point

  2. high resistance and low melting point

  3. low resistance and high melting point

  4. low resistance and low melting point

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Correct Option: B
Explanation:

The safety fuse should have high resistance and low melting point.


Option B is correct.

Charge 1 attracts Charge 2, Charge 2 repels Charge 3, and Charge 3 attracts Charge 4. Which of the following option must hold good for the given condition of four point charges? 

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

  1. Charge 1 attracts Charge 4

  2. Charge 2 attracts Charge 3

  3. Charge 1 repels Charge 3

  4. Charge 2 repels Charge 4

  5. Charge 1 repels Charge 4

Show answer
Correct Option: E
Explanation:

If charge 1 is positive and charge 2 is negative, then charge 1 and 2  will attract. As charge 2 and 3 repels so charge 3 should be negative. Since charge 3 and 4 attracts so charge 4 should be positive. Thus, charge 1 and 4 both are same charge so they will repel. If you take charge 1 is negative and 2 is positive similarly you get 4 is negative so 1 and 4 both have same charge.