Electric Charges and Fields - Bihar Board (BSEB) STD 12 Science Physics Questions

Q 1M.C.Q [1M]1 Mark

The electric flux on a Gaussian spherical surface of radius 15 cm, drawn with a point charge as the centre, is ф. If the radius of this surface is tripled, then the electric flux passing through the surface will be:

A
Zero
B
Infinity
C
3ф
✓
ф

Answer: D.

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Q 2M.C.Q [1M]1 Mark

The value of dielectric strength for air is:

✓
$3 \times 10^6 V / m$
B
$3 \times 10^8 V / m$
C
Zero
D
Infinity

Answer: A.

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Q 3M.C.Q [1M]1 Mark

The SI value of electrical conductivity of free space or vacuum is:

A
$9 \times 10^{\circ} Nm ^2 / C ^2$
B
$-9 \times 10^{\circ} Nm ^2 / C ^2$
✓
$8.854 \times 10^{-12} C ^2 N^{-1} m^{-2}$
D
$8.854 \times 10^{12} C ^2 N^{-1} m^{-2}$

Answer: C.

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Q 4M.C.Q [1M]1 Mark

The SI unit of electric flux is:

✓
$NC ^{-1} m^2$
B
$NC ^{-1} m^-2$
C
$N ^{-1} C ^{-1} m^{-2}$
D
$N ^{-1} C ^{1} m^{2}$

Answer: A.

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Q 5M.C.Q [1M]1 Mark

The magnitude of the electric field due to a point charge at a distance of 4.0 m is 9 N/C. Distance of this point charged substance due to electric field of magnitude 16 N/C will be:

A
1 m
B
2 m
✓
3 m
D
6 m

Answer: C.

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Q 61 Marks Question1 Mark

Draw lines of force due to point charges when
(i) $q<0$ and (ii) $q>0 . \quad$

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Q 71 Marks Question1 Mark

Write the formula to determine the value of electric field intensity due to a uniformly charged thin spherical shell.

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Q 81 Marks Question1 Mark

Write the value of the electric field due to an electric dipole at a point situated on its axis.

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Q 91 Marks Question1 Mark

Can a metal sphere of radius 1 em be given a charge of IC?

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Q 101 Marks Question1 Mark

What is the net flux of uniform elecrtric field of Exercise 1.14 through a cube of side 20 cm oriented so that its faces are parallel to the coordinate planes ?

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Q 11Short Answer Type Questions [2M]2 Marks

(a) An electrostatic field line is a continuous curve. ie., a field line cannot have sudden breaks. Why not?
(b) Explain why two field lines never cross each other at any point.

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Q 12Short Answer Type Questions [2M]2 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 $5 \times 10^4 N C ^{-1}$. Calculate the magnitude of the torque acting on the dipole.

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Q 13Short Answer Type Questions [2M]2 Marks

What is the force between two small charged spheres having charges of 2 x 10^-7C and 3 x 10^-7C placed 30 cm apart in air?

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Q 14Short Answer Type Questions [2M]2 Marks

Do two positively charged balls attract each other?

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Q 15Short Answer Type Questions [2M]2 Marks

If we walk barefoot on a nylon mat for some time and touch the metal handle of a door, we get an electric shock. Why does this happen?

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Q 163 Marks Question3 Marks

A system has two charges $q_A=2.5$$\times 10^{-7} C$ and $q_B=-2.5 \times 10^{-7} C$ located at points A: $(0$,$0,-15 cm)$and $B :( 0 , 0 ,+15 cm)$, respectively. What are the total charge and electric dipole moment of the system?

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Q 173 Marks Question3 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 183 Marks Question3 Marks

(a) Explain the meaning of the statement "electric charge of a body is quantised". (b) Why can one ignore quantisation of electric charge when dealing with macroscopic i.e., large scale charges?

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Q 193 Marks Question3 Marks

An infinite line charge produces a field of 9 x10⁴N C^-1at a distance of 2 cm. Calculate the linear charge density.

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Q 203 Marks Question3 Marks

A conducting sphere of radius 10 cm has an unknown charge. If the electric field 20 cm from the centre of the sphere is $1.5 \times 10^3 N / C$ and directed radially inward, what is the net charge on the sphere?

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Q 214 Marks Questions4 Marks

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 and of magnitude $17.0 \times 10^{-22} C / m ^2$. What is E: (a) in the outer region of the first plate, (b) in the outer re-gion of the second plate, and (c) between the plates?

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Q 224 Marks Questions4 Marks

A uniformly charged conducting sphere of 2.4 m diameter has a surface charge density of$80.0 \mu C / m ^2$.
(a) Find the charge on the sphere.
(b) What is the total electric flux leaving the sur-face of the sphere?

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Q 234 Marks Questions4 Marks

The electrostatic force on a small sphere of charge $0.4 \mu C$ due to another small sphere of charge $-0.8 \mu C$ in air is 0.2 N (a) What is the distance between the two spheres? (b) What is the force on the second sphere due to the first?

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Q 244 Marks Questions4 Marks

Figure shows track of three charged particles in a uniform elecrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

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Q 254 Marks Questions4 Marks

(a) 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 x $10^{-7} C$ ? The radii of A and B are negligible compared to the distance of separation.
(b) 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 26Long Answer Type Questions [5M]5 Marks

By defining electric dipole and dipole moment, find the necessary formula for the field intensity at any point located on the neutral (equatorial plane) of the dipole.

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Q 27Long Answer Type Questions [5M]5 Marks

Write the statement of Gauss's law for electrostatics. Draw a diagram and derive an expression for the electric field due to a uniformly charged infinite plane sheet at a point near it.In the given figure, write the value of electric flux emerging from the surface :

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Q 28Long Answer Type Questions [5M]5 Marks

Prove that due to a charged layer of infinite expansion, the value of the electric field at any point near it does not depend on the area of the surface and the distance from the layer . i.e., the electric field remains uniform at points near the layer.###Write Gauss'law.By applying this rule,find the value of the electric field due to a uniformly charged infinite plane sheet at any point near the sheet.

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Q 29Long Answer Type Questions [5M]5 Marks

Two point charges $q_A=3 \mu C$and $q _{ B }=$$-3 \mu C$ are located 20 cm apart in vacuum.
(a) What is the electric field at the midpoint O of the line AB joining the two charges?
(b) If a negative test charge of magnitude $1.5 \times$$10^{-9} C$ is placed at this point, what is the force experi-enced by the test charge?

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Q 30Long Answer Type Questions [5M]5 Marks

Four point charges $q_{ A }=2 \mu C$,$q_{ B }=-5 \mu C , q_{ C }=2 \mu C$ and $q_{ D }=-5 \mu C$ are located at the of a square ABCD of side 10 cm. Wht is the force on a charge of $1 \mu C$ placed at the centre of the square?