Questions Related to physics

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

It is found that air breaks down electrically, when the electric field is $  3 \times 10^{6} \mathrm{V} / \mathrm{m} .  $ What is the potential to which a sphere of radius $1  \mathrm{m}  $ can be raised, before sparking takes place?

  1. $ V=10^{6} \mathrm{V} $

  2. $ V=2 \times 10^{6} \mathrm{V} $

  3. $ V=3 \times 10^{6} \mathrm{V} $

  4. $ V=4 \times 10^{6} \mathrm{V} $

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

For a charged conducting sphere, the electric field at the surface is E = kQ/R^2 and the potential is V = kQ/R. Therefore, V = E * R. Given E = 3 * 10^6 V/m and R = 1 m, V = 3 * 10^6 V.

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

In moving from A to B along an electric field line, the wok done by the electric field on an electron is $6.4 \times 10^{-19}$ J. If $\phi _1$ and $\phi _2$ are equipotential surfaces, then the potential difference $V _b-V _A $ is

  1. -4V

  2. 4V

  3. zero

  4. 6.4 V

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Work done by the electric field is W = q * (V_A - V_B). For an electron, q = -1.6 * 10^-19 C. Given W = 6.4 * 10^-19 J, we have 6.4 * 10^-19 = -1.6 * 10^-19 * (V_A - V_B), which simplifies to V_A - V_B = -4 V, or V_B - V_A = 4 V.

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

The electric potential in a certain region along the x-axis varies with x according to the relation $V(x) = 5 - 4x^2$. Then, the correct statement is :

  1. the potential difference between the points $x =1$m and $x=2$m is $12$ Volt

  2. the force experienced by a Coulomb of charge placed at $x =1$ m is $8$ Newton

  3. the electric field components along Y and Z direction are zero

  4. all of the above

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$V(x)=5-4x^2$

$V(1)=5-4=1 V,  V(2)=5-4(2^2)=-11 V$

Potential difference between $x=1 m$ and $x=2 m$ is $V _{12}=V _1-V _2=1-(-11)=12 V$

here, $E _x=-\dfrac{dV}{dx}=8x,  E _y=-\dfrac{dV}{dy}=0$ and $E _z=-\dfrac{dV}{dz}=0$

The electric force on $1$ coulomb charge at $x=1$ is $F=qE _x=1(8)=8 N$

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

A point charge q moves from point P to a point S along a path PQRS in a uniform electric field E pointing parallel to the x-axis. The coordinates of P, Q. R and S are $(a, b, 0), (2a, 0, 0), (a, -b, 0)$ and $(0, 0, 0)$. The work done by the field in the above process is :

  1. $zero$

  2. $qEB$

  3. $qEa$

  4. $-qEa$

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

As the field E is uniform, so E is constant at every point.
As E is directed parallel to x axis, so $\vec{E}=E\hat i$
The work done , $W=\int \vec{F}.\vec{dr}=\int qE\hat i.(\hat{i}dx+\hat{j}dy+\hat{k}dz)$
$W=qE\int dx=qE[\int _a^{2a}dx+\int^a _{2a}dx+\int _a^{0}dx]=qE[2a-a+a-2a+0-a]=-qEa$

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

In a certain region of space, the potential is given by : $V = k {[2x^2 - y^2 + z^2]}$. The electric field at the point (1, 1, 1) has magnitude = 

  1. $k\sqrt{6}$

  2. $2k\sqrt{6}$

  3. $2k\sqrt{3}$

  4. $4k\sqrt{3}$

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The electric field is E = -grad(V). E = -(dV/dx i + dV/dy j + dV/dz k). Given V = k(2x^2 - y^2 + z^2), E = -k(4x i - 2y j + 2z k). At (1, 1, 1), E = -k(4 i - 2 j + 2 k). The magnitude is k * sqrt(4^2 + (-2)^2 + 2^2) = k * sqrt(16 + 4 + 4) = k * sqrt(24) = 2k * sqrt(6).

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

A charge of 3C moving in a uniform electric field experiences a force of $3000 N$. The potential difference between two points situated in the field at a distance $1 cm$ from each other will be

  1. $10 V$

  2. $90 V$

  3. $1000 V$

  4. $9000 V$

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The electric field E = F/q = 3000 N / 3 C = 1000 N/C. The potential difference V = E * d. With d = 1 cm = 0.01 m, V = 1000 * 0.01 = 10 V.

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

The potential at a point $x$ (measured in $\mu m )$ due to somecharges situated on the $x$ -axis is given by $V ( x ) = 20 / \left( x ^ { 2 } - 4 \right)$Volts. The electric field $E$ at $x = 4 \mu m$ is given by

  1. 5$/ 3$ Volt / \mum and in the -ve $x$ direction

  2. 5$/ 3$ Volt $/ \mu m$ and in the +ve $x$ direction

  3. 10$/ 9$ Volt / \mum and in the -ve $x$ direction

  4. 10$/ 9$ Volt $/ \mu m$ and in the +ve $x$ direction

Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

Variation in potential is maximum if one goes :

  1. along the line of force

  2. perpendicular to the line of force

  3. in any direction

  4. none of these

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$dV=-\vec{E}.d\vec{r}=-Edr cos\theta$


Hence, variation will be maximimum for $\theta=0^{o}$ or $180^{o}$, that is variation $dV$ is maximum along line of field or say line of force.

Answer-(A)

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

The electric field lines are closer together near object $A$ than they are near object $B$. We can conclude that :

  1. the potential near $A$ is greater than the potential near $B$

  2. the potential near $A$ is less than the potential near $B$

  3. the potential near $A$ is equal to the potential near $B$

  4. nothing about the relative potentials near $A$ and $B$

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Potential decreases in the direction of electric field. So it depends  on whether the lines of forces are from $A$ to $B$ or from $B$ to $A$.