Electric Charges Fields And Gauss Law(12th Grade > Physics ) Questions and answers for exam Preparation

12th Grade > Physics

ELECTRIC CHARGES FIELDS AND GAUSS LAW MCQs

Total Questions : 30 | Page 3 of 3 pages

Question 21. Electric lines of force about negative point charge are

Circular, anticlockwise
Circular, clockwise
Radial, inward
Radial, outward

Discuss Question

Answer: Option C. -> Radial, inward
:
C

Electric Lines Of Force About Negative Point Charge Are

Question 22.

Discuss Question

Answer: Option C. -> Radial, inward
:
D
The force is perpendicular to the displacement.

Question 23. Three positive charges of equal value q are placed at the vertices of an equilateral triangle. The resulting lines of force should be sketched as in

Discuss Question

Answer: Option C. -> Radial, inward
:
C
Option (a) shows lines of force starting from one positive charge and terminating at another. Option (b) has one line of force making closed loop. Option (d) shows all lines making closed loops. All these are not correct. Only option (c) is correct.

Question 24. Two parallel plane sheets 1 and 2 carry uniform charge densities

σ_{1}

and

σ_{2}

as in fig electric field in the region marked II is (

σ_{1}

σ_{2}

)

Two Parallel Plane Sheets 1 And 2 Carry Uniform Charge Densi...

−(σ1+σ2)2ϵ0
−(σ1 σ2)2ϵ0
(σ1+σ2)2ϵ0
(σ1−σ2)2ϵ0
If assertion is false but reason is true.

Discuss Question

Answer: Option D. -> (σ1−σ2)2ϵ0
:
D

E = E_{1} - E_{2}

= \frac{σ_{1}}{2 ϵ_{0}} - \frac{σ_{2}}{2 ϵ_{0}}

E = \frac{σ_{1} - σ_{2}}{2 ϵ_{0}}

Question 25. A cube is arranged such that its length, breadth and height are along X, Y and Z directions. One of its corners is situated at the origin. Length of each side of the cube is 25 cm. The components of electric field are

E_{x} = 400 \sqrt{2} N / C, E_{y} = 0 a n d E_{z} = 0

respectively. Find the flux coming out of the cube at one end.

25
25√2
25√2
zero
If assertion is false but reason is true.

Discuss Question

Answer: Option C. -> 25√2
:
C

Φ_{x} = E_{x} A c o s (0)

= 400 \sqrt{2} \times \frac{1}{4} \times \frac{1}{4}

= \frac{400 \sqrt{2}}{16} = 25 \sqrt{2}

Question 26. The minimum charge on an object is

1 coulomb
1 stat coulomb

Discuss Question

Answer: Option C. -> 25√2
:
C
This is the charge of an electron. It is the minimum charge possible. All other charges are its integral multiple.

Question 27. The electric field inside a spherical shell of uniform surface charge density is

Zero
Constant, less than zero
Directly proportional to the distance from the centre
None of the above

Discuss Question

Answer: Option A. -> Zero
:
A
All charge resides on the outer surface so that according to Gauss law, electric field inside a shell is zero.

Question 28. The intensity of the electric field required to keep a water drop of radius

10^{- 5}

cm, just suspended in air when charged with one electron is approximately (g = 10newton / kg, e

= 1.6 \times 10^{- 19}

coulomb)

260 volt / cm
260 newton / coulomb
130 volt / cm
130 newton / coulomb
If assertion is false but reason is true.

Discuss Question

Answer: Option B. -> 260 newton / coulomb
:
B
For balance

m g = e E \Rightarrow E = \frac{m g}{e}

Also

m = \frac{4}{3} π r^{3} d = \frac{4}{3} \times \frac{22}{7} \times (10^{- 7})^{3} \times 1000 k g

\Rightarrow E = \frac{4 / 3 \times 22 / 7 \times (10^{- 7})^{3} \times 1000 \times 10}{1.6 \times 10^{- 19}} = 260 N / C

Question 29. Assertion : Electric lines of force cross each other.
Reason : Electric field at a point superimpose to give one resultant electric field.

If both assertion and reason are true and the reason is the correct explanation of the assertion.
If both assertion and reason are true but reason is not the correct explanation of the assertion.
If assertion is true but reason is false.
If the assertion and reason both are false.
If assertion is false but reason is true.

Discuss Question

Answer: Option E. -> If assertion is false but reason is true.
:
E
If electric lines of forces cross each other, then the electric field at the point of intersection will have two direction simultaneously which is not possible physically.

Question 30. A cylinder of radius R and length L is placed in a uniform electric field E parallel to the cylinder axis. The total flux from the curved surface of the cylinder is given by