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Electric Charges and Fields Set-1 MCQ Online Practice Test | Class 12 | Quiz Tweek

Electric Charges and Fields Set-1

Practice Important MCQs for Electric Charges and Fields — Physics, Class 12.

Mastery of "Electric Charges and Fields" is crucial for Class 12 board exams and competitive tests (JEE/NEET) because it builds the foundation for electrostatics problems that test reasoning, superposition, symmetry and Gauss's law. Problems in this chapter combine vector addition, calculus and physical insight; doing varied problems improves accuracy in both objective and long-answer formats.

Beyond routine formula use, this chapter trains you to interpret fields and potentials, reason about conductors and cavities, and read field/ potential behaviour from graphs or experimental data—skills repeatedly tested in higher-level competitive questions and board-style numerical/AR reasoning problems.

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Q1. Two point charges $+4.0\ \mu\text{C}$ and $+1.0\ \mu\text{C}$ are fixed on the x-axis at $x=0$ and $x=3.0\ \text{m}$ respectively. At what point (value of $x$ measured from the origin) on the line joining them is the resultant electric field zero?

(A)

$x=2.0\ \text{m}$

(B)

$x=1.0\ \text{m}$

(C)

$x=1.5\ \text{m}$

(D)

$x=2.5\ \text{m}$

Q2. Assertion (A): The electric field at every point inside a hollow metallic sphere in electrostatic equilibrium is zero. Reason (R): Excess charge on an isolated conductor in electrostatic equilibrium resides only on its outer surface.

(A)

Both A and R are true and R is the correct explanation of A

(B)

Both A and R are true but R is not the correct explanation of A

(C)

A is true but R is false

(D)

A is false but R is true

Q3. A uniformly charged thin ring of radius $R=0.10\ \text{m}$ carries total charge $Q=5.0\times10^{-6}\ \text{C}$ . The axial field is $E(x)=\dfrac{1}{4\pi\varepsilon_0}\dfrac{Qx}{(x^2+R^2)^{3/2}}$ . At what magnitude does the axial electric field attain its maximum value?

(A)

$1.73\times10^{6}\ \text{N/C}$

(B)

$3.46\times10^{6}\ \text{N/C}$

(C)

$8.66\times10^{5}\ \text{N/C}$

(D)

$2.60\times10^{6}\ \text{N/C}$

Q4. A solid non-conducting sphere of radius $R=0.10\ \text{m}$ carries total charge $Q=8.0\times10^{-6}\ \text{C}$ uniformly distributed in its volume. What is the magnitude of the electric field at a point $r=0.05\ \text{m}$ from the centre?

(A)

$3.6\times10^{6}\ \text{N/C}$

(B)

$7.2\times10^{6}\ \text{N/C}$

(C)

$9.0\times10^{5}\ \text{N/C}$

(D)

$1.8\times10^{7}\ \text{N/C}$

Q5. Assertion (A): The electric potential is continuous across a surface that carries surface charge (no finite jump in $V$ ). Reason (R): The normal component of the electric field across a surface carrying surface charge density $\sigma$ has a discontinuity given by $\dfrac{\sigma}{\varepsilon_0}$ .

(A)

Both A and R are true and R is the correct explanation of A

(B)

Both A and R are true but R is not the correct explanation of A

(C)

A is true but R is false

(D)

A is false but R is true

Q6. A point charge $q=2.0\times10^{-6}\ \text{C}$ is held at a distance $d=5.0\times10^{-2}\ \text{m}$ from an infinite grounded conducting plane. Using the method of images, what is the magnitude and direction of the electrostatic force on $q$ ?

(A)

$3.6\ \text{N}$ toward the plane

(B)

$3.6\ \text{N}$ away from the plane

(C)

$1.8\ \text{N}$ toward the plane

(D)

$0\ \text{N}$

Q7. Two point charges $+Q$ and $-Q$ with $Q=2.0\times10^{-6}\ \text{C}$ are located at $x=-a$ and $x=+a$ respectively with $2a=0.10\ \text{m}$ . At the midpoint $x=0$ , what are the electric potential and the electric field (magnitude and direction)?

(A)

$V=0,\quad E=1.44\times10^{7}\ \text{N/C}$ directed from $+Q$ toward $-Q$

(B)

$V=0,\quad E=0\ \text{N/C}$

(C)

$V=1.8\times10^{5}\ \text{V},\quad E=0$

(D)

$V=0,\quad E=1.44\times10^{7}\ \text{N/C}$ directed from $-Q$ toward $+Q$

Q8. Assertion (A): If the electric potential at a point is zero, then the electric field at that point must be zero. Reason (R): A zero value of potential at a point implies all spatial derivatives of the potential at that point are zero.

(A)

Both A and R are true and R is the correct explanation of A

(B)

Both A and R are true but R is not the correct explanation of A

(C)

A is true but R is false

(D)

A is false but R is false

Q9. Three qualitative curves of electric field magnitude $E$ versus radial distance $r$ from the origin are described:

Curve (A): $E\to\infty$ as $r\to0$ and for large $r$ behaves as $E\propto 1/r^{2}$ .

Curve (B): $E=0$ at $r=0$ , rises to a maximum at $r=R/\sqrt{2}$ , then for large $r$ behaves as $E\propto 1/r^{2}$ .

Curve (C): $E\to\infty$ as $r\to0$ and for large $r$ behaves as $E\propto 1/r$ .

Which assignment of physical charge-distributions to curves (A,B,C) is correct?

(A)

(A) point charge at origin; (B) uniformly charged ring (field on axis); (C) infinite straight line charge

(B)

(A) infinite line charge; (B) point charge; (C) uniformly charged ring

(C)

(A) uniformly charged ring; (B) infinite line charge; (C) point charge

(D)

(A) point charge; (B) infinite line charge; (C) uniformly charged ring

Q10. Experimental data for a spherically symmetric charge distribution show: for $r<a$ , $E(r)\propto r$ ; for $r>a$ , $E(r)\propto 1/r^{2}$ . Which charge distribution best matches these measurements?

(A)

Uniform volume charge density filling a sphere of radius $a$

(B)

Thin spherical shell of radius $a$

(C)

Point charge located at the centre

(D)

Infinite line charge passing through the centre

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