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Multiple choice physics static electricity properties of charges charge properties of charge

$\displaystyle \frac {4}{25}$ Coulomb of charge contains .................. electrons: 

  1. $10^{15}$

  2. $10^{18}$

  3. $10^{20}$

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

Answer is C.

The formula for quantisation of charge is given as q=ne.
where, q is the amount of charge in Coulumbs, n is the number of charges and e is the charge on the electron.
In this case, q=4/25 C
So, e = $1.6\times { 10 }^{ -19 }C$.
n can be calculated as n=q/e = $\frac { 4 }{ 25 } \times [\frac { 1 }{ 1.6\times { 10 }^{ -19 }C } ]\quad =\quad { 10 }^{ 18 }$ which is the number of electrons.
Hence, 4/25 Coulomb of charge contains ${ 10 }^{ 18 }$ electrons:.

Multiple choice physics static electricity properties of charges charge properties of charge

Two metallic spheres, one hollow and the other solid, have same diameter. The hollow sphere will hold charge

  1. Same as the solid sphere

  2. 2 times as the solid sphere

  3. $\displaystyle\frac{1}{2}$ times as the solid sphere

  4. Zero
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The capacity of the metallic sphere is proportional to the radius. It does not matter whether it is solid or hollow. Therefore the hollow sphere will hold same charge as the solid sphere.

Multiple choice physics static electricity properties of charges charge properties of charge

Quantisation of charge implies

  1. charge does not exiet

  2. charge exists on particles

  3. there is a minimum permissible magnitude of charge

  4. charge can't be created
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The word quantised means any quantity is an integral multiple of a minimum value and cannot have any value equal to decimal multiples.

The minimum charge that exists in nature is $1.6\times10^{-19}$ coulombs.
It is the positive value for one proton and negative for an electron.
Any charged body has a positive charge if electrons are less than needed and vice-versa.
Whatever may be the case, the magnitude of charge is always an integral multiple of $1.6\times10^{-19}$ coulombs.
Thus charge is quantised.

Multiple choice physics static electricity properties of charges charge properties of charge

Charge on a body can be :

  1. $\displaystyle -1.3e$

  2. $\displaystyle 0.9e$

  3. $\displaystyle \pm 3e$

  4. $\displaystyle 1.5e$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Charge on a body is always $\displaystyle \pm e$, $\displaystyle \pm 2e$, $\displaystyle \pm 3e$. It can't be in fraction of e i.e 1.5e, 0.9e or -1.2e. The electronic charge is the minimum possible charge.

Multiple choice physics static electricity properties of charges charge properties of charge

A point charge $+q$ is placed at the centre of a cube of side L. The electric flux emerging from the cube is

  1. $\dfrac{q}{\varepsilon _0}$

  2. Zero

  3. $\dfrac{6qL^2}{\varepsilon _0}$

  4. $\dfrac{q}{6L^2\varepsilon _0}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since the charge is placed at the centre of the cube, so the electric flux lines move out equally from all sides of the cube. Thus the electric flux emerging from the cube is equal to $\dfrac{q}{\varepsilon _0}$.