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Electric Charges and Fields Physics - Electric Charges and Fields

Uttarakhand Board (UBSE) - STD 12 Science - Physics (Uttarakhand - English Medium). 593 questions in this chapter.

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Electric Charges and Fields question types

593 questions across 7 question groups — pick any mix to generate a Physics paper with step-by-step answer keys.

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Sample Questions

Electric Charges and Fields questions

One sample from each question group in this chapter. Select any group above to see the full set with answer keys.

Q 1M.C.Q (1 Marks)1 Mark
If the net electric flux through a closed surface is zero, then we can infer:
  • ✓
    No net charge is enclosed by the surface.
  • B
    Uniform electric field exists within the surface.
  • C
    Electric potential varies from point to point inside the surface.
  • D
    Charge is present inside the surface.

Answer: A.

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Q 2M.C.Q (1 Marks)1 Mark
Which group among the following is insulator?
  • A
    Silver, copper, gold
  • ✓
    Paper, glass, cotton
  • C
    The human body, wood, iron
  • D
    Glass, copper, paper

Answer: B.

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Q 3M.C.Q (1 Marks)1 Mark
As shown in figure a dust particle with mass $m =5.0 \times 10^{-9} kg$ and charge $q ^{\circ}=2.0 nC$ starts from rest at point a and moves in a straight line to point $b.$ What is its speed $v$ at point $b\ ? $
  • A
    $26 ms^{-1}$
  • B
    $34 ms^{-1}$
  • ✓
    $46 ms^{-1}$
  • D
    $14 ms^{-1}$

Answer: C.

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Q 5M.C.Q (1 Marks)1 Mark
Why is gold used in the Gold$-$leaf electroscope?
  • A
    Gold is easily available in nature.
  • ✓
    Gold is malleable.
  • C
    Gold is conducting in nature.
  • D
    Gold is cheap.

Answer: B.

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Q 6Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given$-$one labelled Assertion $(A)$ and the other labelled Reason $(R)$. Select the correct answer to these questions from the codes $(a), (b), (c)$ and $(d)$ as given below.
Assertion $(A):$ Charge is quantized.
Reason $(R):$ Charge which is less than $\text{IC}$ is not possible.
  • 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 $A$
  • ✓
    $A$ is true but $R$ is false.
  • D
    $A$ is false and $R$ is also false.

Answer: C.

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Q 7Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
Assertion (A): The electric tines of forces diverges from a positive charge and converge at a negative charge.
​​​​​​​Reason (A): A charged particle free to move in an electric field always move along an electric line of force.
  • 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.
  • ✓
    A is true but R is false.
  • D
    A is false and R is also false.

Answer: C.

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Q 8Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
Assertion (A): If there exists coulomb attraction between two bodies, both of them may not be charged.
​​​​​​​Reason (R): ln coulomb attraction two bodies are oppositely charged.
  • A
    Both A and R are true, and R is the correct explanation of A.
  • ✓
    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 and R is also false.

Answer: B.

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Q 9Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
​​​​​​​Assertion (A): If a conducting medium is placed between two charges, then electric force between them becomes zero.
Reason (R): Reduction in a force due to introduced material is inversely proportional to its dielectric constant.
  • ✓
    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 and R is also false.

Answer: A.

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Q 10Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion (A): For charge to be in equilibrium, sum of the forces on charge due to rest of the two charges must be zero.
Reason (R): A charge is lying at the centre of the line joining two similar charges each which are fixed. The system will be in equilibrium if that charge is one fourth of the similar charges.
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Q 111 Marks Question1 Mark
What is the net flux of the uniform electric field of Exercise 1.15 through a cube of side 20 cm oriented so that its faces are parallel to the coordinate planes?
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Q 151 Marks Question1 Mark
Two equal balls having equal positive charge ‘q’ coulombs are suspended by two insulating strings of equal length. What would be the effect on the force when a plastic sheet is inserted between the two?
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Q 162 Marks Questions2 Marks
  1. An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
  2. Explain why two field lines never cross each other at any point?
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Q 182 Marks Questions2 Marks
A uniformly charged conducting sphere of 2.4 m diameter has a surface charge density of $80.0\ μC/m^2$.
  1. Find the charge on the sphere.
  2. What is the total electric flux leaving the surface of the sphere?
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Q 192 Marks Questions2 Marks
When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.
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Q 202 Marks Questions2 Marks
An oil drop of 12 excess electrons is held stationary under a constant electric field of $2.55 \times 10^4 \mathrm{NC}^{-1}$ in Millikan's oil drop experiment. The density of the oil is $1.26 \mathrm{~g} \mathrm{~cm}^{-3}$. Estimate the radius of the drop. $\left(\mathrm{g}=9.81 \mathrm{~m} \mathrm{~s}^{-2} ; \mathrm{e}=1.60 \times 10^{-19} \mathrm{C}\right)$.
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Q 213 Marks Question3 Marks
  1. Drive the expression for electric field at a point on the equatorial line of an electric dipole.
  2. Depict the orientation of the dipole in (i) stable, (ii) unstable equilibrium in a uniform electric field.
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Q 233 Marks Question3 Marks
An electric dipole with dipole moment $4 \times 10^{-9}$ Cm is aligned at 30^\circ with the direction of a uniform electric field of magnitude $5 \times 10^4 NC^{-1}.$ Calculate the magnitude of the torque acting on the dipole.
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Q 243 Marks Question3 Marks
Suppose that the particle in Exercise in 1.33 is an electron projected with velocity $v_x= 2.0 \times 10^6 m s^{–1}$. If E between the plates separated by 0.5 cm is $9.1 \times 10^2N/C,$ where will the electron strike the upper plate? $(|e|=1.6 \times 10^{–19}C, m_e = 9.1 \times 10^{–31} kg.)$
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Q 253 Marks Question3 Marks
Figure 1.33 shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?
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Q 265 Marks Questions5 Marks
  1. Two insulated charged copper spheres A and B have their centres separated by a distance of 50 cm. What is the mutual force of electrostatic repulsion if the charge on each is $6.5 \times 10^{-7}$ C? The radii of A and B are negligible compared to the distance of separation.
  2. What is the force of repulsion if each sphere is charged double the above amount, and the distance between them is halved?
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Q 275 Marks Questions5 Marks
It is now believed that protons and neutrons (which constitute nuclei of ordinary matter) are themselves built out of more elementary units called quarks. A proton and a neutron consist of three quarks each. Two types of quarks, the so called ‘up’ quark (denoted by u) of charge + (2/3) e, and the ‘down’ quark (denoted by d) of charge (–1/3) e, together with electrons build up ordinary matter. (Quarks of other types have also been found which give rise to different unusual varieties of matter.) Suggest a possible quark composition of a proton and neutron.
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Q 285 Marks Questions5 Marks
In a certain region of space, electric field is along the z-direction throughout. The magnitude of electric field is, however, not constant but increases uniformly along the positive z-direction, at the rate of $10^5$ $NC^{-1}$ per metre. What are the force and torque experienced by a system having a total dipole moment equal to $10^{-7}$ Cm in the negative z-direction?
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Q 295 Marks Questions5 Marks
A point charge causes an electric flux of $–1.0 \times 10^3\ Nm^2 /C$ to pass through a spherical Gaussian surface of 10.0 cm radius centred on the charge.
  1. If the radius of the Gaussian surface were doubled, how much flux would pass through the surface?
  2. What is the value of the point charge?
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Q 305 Marks Questions5 Marks
A system has two charges $\mathrm{q}_{\mathrm{A}}=2.5 \times 10^{-7} \mathrm{C}$ and $\mathrm{q}_{\mathrm{B}}=-2.5 \times 10^{-7} \mathrm{C}$ located at points $\mathrm{A}:(0,0,-15 \mathrm{~cm})$ and $\mathrm{B}:(0,0,+15 \mathrm{~cm})$, respectively. What are the total charge and electric dipole moment of the system?
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Q 31Case study (4 Marks)4 Marks
The electric current flowing in a wire in the direction from B to A is decreasing. Find out the direction of the induced current in the metallic loop kept above the wire as shown.
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Q 32Case study (4 Marks)4 Marks
Surface charge density is defined as charge per unit surface area of surface charge distribution. i.e., $\sigma=\frac{\text{dq}}{\text{dS}}.$ Two large, thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs having magnitude of $17.0 \times 10^{-22}Cm^{-2}$ as shown. The intensity of electric field at a point is $\text{E}=\frac{\sigma}{\in_0},$ where$\in_0=$ permittivity of free space.
  1. E in the outer region of the first plate is:
  1. $17 \times 10^{-22} N/C$
  2. $1.5 \times 10^{-25} N/C$
  3. $1.9 \times 10^{-10} N/C$
  4. Zero.
  1. E in the outer region of the second plate is:
  1. $17 \times 10^{-22} N/C$
  2. $1.5 \times 10^{-15} N/C$
  3. $1.9 \times 10^{-10} N/C$
  4. Zero.
  1. E between the plates is:
  1. $17 \times 10^{-22} N/C$
  2. $1.5 \times 10^{-15} N/C$
  3. $1.9 \times 10^{-10} N/C$
  4. Zero.
  1. The ratio of E from right side of B at distances 2cm and 4cm, respectively is:
  1. 1 : 2
  2. 2 : 1
  3. 1 : 1
  4. $1:\sqrt{2}$
  1. ln order to estimate the electric field due to a thin finite plane metal plate, the Gaussian surface considered is:
  1. Spherical.
  2. Spherical.
  3. Straight line.
  4. None of these.
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Q 33Case study (4 Marks)4 Marks
Coulomb's law states that the electrostatic force of attraction or repulsion acting between two stationary point charges is given by: $\text{F}=\frac{1}{4\pi\in_0}\frac{\text{q}_1\text{q}_2}{\text{r}^2}$

Where F denotes the force between two charges $q_1$ and $q_2$ separated by a distance r in free space, $\in_0$ is a constant known as permittivity of free space. Free space is vacuum and may be taken to be air practically. If free space is replaced by a medium, then $\in_0$ is replaced by $(\in_0\text{k})$ or $(\in_0\in_\text{r})$ where k is known as dielectric constant or relative permittivity.
  1. In coulomb's law, $\text{F}=\text{k}\frac{\text{q}_1\text{q}_2}{\text{r}^2}$ then on which of the following factors does the proportionality constant k depends?
  1. Electrostatic force acting between the two charges.
  2. Nature of the medium between the two charges.
  3. Magnitude of the two charges.
  4. Distance between the two charges.
  1. Dimensional formula for the permittivity constant $\in_0$ of free space is:
  1. $[ML^{-3}T^4 A^2]$
  2. $[M^{-1} L^3 T^2 A^2]$
  3. $[M^{-1} L^{-3} T^4 A^2]$
  4. $[ML^{-3} T^4 A^{-2}]$
  1. The force of repulsion between two charges of 1C each, kept 1m apart in vaccum is:
  1. $\frac{1}{9\times10^9}\text{N}$
  2. $9 \times 10^9N$
  3. $9 \times 10^7N$
  4. $\frac{1}{9\times10^{12}}\text{N}$
  1. Two identical charges repel each other with a force equal to 10 mgwt when they are 0.6m apart in air.$(g = 10m s^{-2}).$ The value of each charge is:
  1. 2mC
  2. $2 \times 10^{-7}mC$
  3. 2 nC
  4. $2\mu\text{C}$
  1. Coulomb's law for the force between electric charges most closely resembles with:
  1. Law of conservation of energy.
  2. Newton's law of gravitation.
  3. Newton's $2^{nd}$ law of motion.
  4. Law of conservation of charge.
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Q 34Case study (4 Marks)4 Marks
Net electric flux through a cube is the sum of fluxes through its six faces. Consider a cube as shown in figure, having sides of length L = 10.0cm. The electric field is uniform, has a magnitude $E = 4.00 \times 10^3N C^{-1}$ and is parallel to the xy plane at an angle of 37º measured from the + x - axis towards the + y - axis.
  1. Electric flux passing through surface $S_6$ is:
  1. $-24N\ m^2C^{-1}$
  2. $24N\ m^2C^{-1}$
  3. $32N\ m^2C^{-1}$
  4. $-32N\ m^2C^{-1}$
  1. Electric flux passing through surface $S_1$ is:
  1. $-24N\ m^2C^{-1}$
  2. $24N\ m^2 C^{-1}$
  3. $32N\ m^2 C^{-1}$
  4. $-32N\ m^2 C^{-1}$
  1. The surfaces that have zero flux are:
  1. $S_1$ and $S_3$
  2. $S_5$ and $S_6$
  3. $S_2$ and $S_4$
  4. $S_1$ and $S_2$
  1. The total net electric flux through all faces of the cube is:
  1. 8N $m^2\ C^{-1}$
  2. -8N $m^2\ C^{-1}$
  3. 24N $m^2\ C^{-1}$
  4. Zero.
  1. The dimensional formula of surface integral $\oint\vec{\text{E}}\cdot\text{d}\vec{\text{S}}$ of an electric field is:
  1. $[M\ L^2T^{-2} A^{-1}]$
  2. $[M\ L^3T^{-3} A^{-1}]$
  3. $[M\ L^{-1}T^3 A^{-3}]$
  4. $[M\ L^{-3}T^{-3} A^{-1}]$
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Q 35Case study (4 Marks)4 Marks
In 1909, Robert Millikan was the first to find the charge of an electron in his now-famous oil-drop experiment. In that experiment, tiny oil drops were sprayed into a uniform electric field between a horizontal pair of oppositely charged plates. The drops were observed with a magnifying eyepiece, and the electric field was adjusted so that the upward force on some negatively charged oil drops was just sufficient to balance the downward force of gravity. That is, when suspended, upward force qE just equaled Mg. Millikan accurately measured the charges on many oil drops and found the values to be whole number multiples of $1.6 \times 10^{-19}C$ the charge of the electron. For this, he won the Nobel Prize.
  1. If a drop of mass $1.08 \times 10^{-14}kg$ remains stationary in an electric field of $1.68 \times 10^5NC^{-1},$ then the charge of this drop is:
  1. $6.40 \times 10^{-19}C$
  2. $3.2 \times 10^{-19}C$
  3. $1.6 \times 10^{-19}C$
  4. $4.8 \times 10^{-19}C$
  1. Extra electrons on this particular oil drop (given the presently known charge of the electron) are:
  1. 4
  2. 3
  3. 5
  4. 8
  1. A negatively charged oil drop is prevented from falling under gravity by applying a vertical electric field $100V\  m^{-1}.$ If the mass of the drop is $1.6 \times 10^{-3}g,$ the number of electrons carried by the drop is$ (g = 10m s^{-2})$
  1. $10^{18}$
  2. $10^{15}$
  3. $10^{12}$
  4. $10^9$
  1. The important conclusion given by Millikan's experiment about the charge is:
  1. Charge is never quantized.
  2. Charge has no definite value.
  3. Charge is quantized.
  4. Charge on oil drop always increases.
  1. If in Millikan's oil drop experiment, charges on drops are found to be $8\mu\text{C, }12\mu\text{C, }20\mu\text{C, }$ then quanta of charge is:
  1. $8\mu\text{C}$
  2. $20\mu\text{C}$
  3. $12\mu\text{C}$
  4. $4\mu\text{C}$
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