ELECTRONIC DEVICES | Energy | PHYSICS | CUET JEE | SELF STUDY | CBSE

 

PHYSICS  |  Class XII

Chapter 14

ELECTRONIC DEVICES

Semiconductor Electronics

Energy Bands  ◆  p-n Diode  ◆  Transistors  ◆  Logic Gates  ◆  Rectifiers

Gauss’s Law & Flux | 1 MARKS QUESTION 👀 | PHYSICS | APNA CAREER

 

Gauss’s Law & Flux

1 MARKS QUESTION 👀

1. What is electric flux?

Answer: Measure of electric field passing through a surface

Explanation: Indicates number of field lines.

---

2. What is symbol of electric flux?

Answer: 

$\mathrm{\Phi }$

Explanation: Greek letter phi.

---

3. What is formula of electric flux?

Answer:

$\mathrm{\Phi }=EA\cos \theta$

Explanation: Depends on area and angle.

---

4. What is SI unit of electric flux?

Answer: 

$N{m}^2\mathrm{/}C$

Explanation: Derived unit.

---

5. What is Gauss’s Law?

Answer: Total flux = enclosed charge / ε₀

Explanation: Fundamental electrostatics law.

---

6. Write Gauss’s Law formula.

Answer:

$\mathrm{\Phi }=\frac{Q_{enc}}{{\epsilon }_0}$

---

7. What is a Gaussian surface?

Answer: Imaginary closed surface

Explanation: Used to apply Gauss law.

---

8. What is flux when field is perpendicular to surface?

Answer: Maximum

Explanation: 

$\theta =0^{\circ }$

---

9. What is flux when field is parallel to surface?

Answer: Zero

Explanation: 

$\theta ={90}^{\circ }$

---

10. What is ε₀?

Answer: Permittivity of free space

Explanation: Constant value.

---

11. What is value of ε₀?

Answer: 

$8.85\times {10}^{-12}F\mathrm{/}m$

Explanation: Standard constant.

---

12. What type of quantity is electric flux?

Answer: Scalar

Explanation: No direction.

---

13. What is flux through closed surface with no charge inside?

Answer: Zero

Explanation: No enclosed charge.

---

14. What is area vector direction?

Answer: Normal to surface

Explanation: Outward for closed surface.

---

15. What is closed surface?

Answer: Surface enclosing volume

Explanation: No open edges.

---

16. What is open surface?

Answer: Surface with boundary

Explanation: Does not enclose volume.

---

17. What does positive flux indicate?

Answer: Outward field lines

Explanation: Leaving surface.

---

18. What does negative flux indicate?

Answer: Inward field lines

Explanation: Entering surface.

---

19. What is Gauss law based on?

Answer: Inverse square law

Explanation: Coulomb’s law.

---

20. What does flux depend on?

Answer: Field, area, angle

Explanation: From formula.

---

🔹 21–35 (Conceptual Understanding)

21. Does flux depend on shape of surface?

Answer: No

Explanation: Depends only on enclosed charge.

---

22. What is flux if charge lies outside surface?

Answer: Zero

Explanation: Not enclosed.

---

23. What is flux proportional to?

Answer: Electric field strength

Explanation: Stronger field → more flux.

---

24. What is flux through sphere enclosing charge Q?

Answer:

$$$$Φ=Qε0

Explanation: Gauss law.

---

25. What is flux through cube enclosing charge?

Answer: Same as sphere

Explanation: Shape independent.

---

26. What is electric field inside conductor?

Answer: Zero

Explanation: Electrostatic equilibrium.

---

27. Where do charges reside in conductor?

Answer: On surface

Explanation: Repulsion spreads charges.

---

28. What is field direction at conductor surface?

Answer: Perpendicular

Explanation: No tangential component.

---

29. What is flux for uniform field?

Answer: Easy to calculate

Explanation: Constant field.

---

30. What is net flux for equal inward and outward lines?

Answer: Zero

Explanation: Cancel out.

---

31. What is Gaussian surface used for?

Answer: Calculating electric field

Explanation: Simplifies problems.

---

32. What is symmetry requirement in Gauss law?

Answer: High symmetry

Explanation: For easy application.

---

33. What is flux for curved surface?

Answer: Depends on angle

Explanation: Orientation matters.

---

34. What is total flux through closed surface?

Answer: Algebraic sum

Explanation: Add all contributions.

---

35. What is electric field lines relation to flux?

Answer: Flux ∝ number of lines

Explanation: Representation.

---

🔹 36–50 (Applications & Key Results)

36. What is electric field due to spherical charge using Gauss law?

Answer:

$E=\frac{1}{4\pi {\epsilon }_0}\frac{Q}{r^2}$

Explanation: Same as point charge.

---

37. What is electric field inside hollow sphere?

Answer: Zero

Explanation: No enclosed charge.

---

38. What is electric field outside sphere?

Answer: Like point charge

Explanation: Radial field.

---

39. What is field due to infinite plane sheet?

Answer: Constant

Explanation: Independent of distance.

---

40. What is flux through plane sheet?

Answer: Depends on area

Explanation: Uniform field.

---

41. What is electric field due to infinite line charge?

Answer: Decreases with distance

Explanation: Cylindrical symmetry.

---

42. What is Gaussian surface for line charge?

Answer: Cylinder

Explanation: Matches symmetry.

---

43. What is Gaussian surface for sphere?

Answer: Sphere

Explanation: Radial symmetry.

---

44. What is Gaussian surface for plane?

Answer: Pillbox

Explanation: Flat symmetry.

---

45. What is field inside cavity of conductor?

Answer: Zero

Explanation: Shielding.

---

46. What is flux through hemisphere?

Answer: Half of sphere

Explanation: Symmetry.

---

47. What is importance of Gauss law?

Answer: Simplifies field calculation

Explanation: Powerful tool.

---

48. What is flux independent of?

Answer: Surface shape

Explanation: Depends only on charge.

---

49. What is electric field relation with flux?

Answer: Field produces flux

Explanation: Field lines pass through area.

---

50. What is summary of Gauss’s Law?

Answer: Flux depends only on enclosed charge

Explanation: Fundamental principle.

51. What is electric field inside a conductor?

Answer: Zero

Explanation: Charges rearrange to cancel field.

---

52. What is electric field just outside a conductor?

Answer: Perpendicular to surface

Explanation: No tangential component.

---

53. What is flux through closed surface enclosing no charge?

Answer: Zero

Explanation: From Gauss’s law.

---

54. What is flux through closed surface enclosing charge Q?

Answer:

$\mathrm{\Phi }=\frac{Q}{{\epsilon }_0}$

---

55. What is flux if charge is outside the surface?

Answer: Zero

Explanation: Not enclosed.

---

56. What is Gaussian surface for spherical symmetry?

Answer: Sphere

Explanation: Matches symmetry.

---

57. What is Gaussian surface for line charge?

Answer: Cylinder

Explanation: Cylindrical symmetry.

---

58. What is Gaussian surface for plane sheet?

Answer: Pillbox

Explanation: Flat symmetry.

---

59. What is electric field due to spherical charge?

Answer:

$E=\frac{1}{4\pi {\epsilon }_0}\frac{Q}{r^2}$

---

60. What is field inside hollow sphere?

Answer: Zero

Explanation: No enclosed charge.

---

61. What is field outside charged sphere?

Answer: Like point charge

Explanation: Radial field.

---

62. What is electric field due to infinite plane sheet?

Answer: Constant

Explanation: Independent of distance.

---

63. What is field due to infinite line charge?

Answer: Decreases with distance

Explanation: 

$\propto \frac{1}{r}$

---

64. What is flux through hemisphere?

Answer: Half of total sphere flux

Explanation: Symmetry.

---

65. What is flux through cube enclosing charge?

Answer: Same as any shape

Explanation: Shape independent.

---

66. What is flux proportional to enclosed charge?

Answer: Directly proportional

Explanation: From Gauss law.

---

67. What is flux independent of?

Answer: Surface shape

Explanation: Only depends on charge.

---

68. What is direction of area vector for closed surface?

Answer: Outward

Explanation: Convention.

---

69. What is sign of flux for outward field lines?

Answer: Positive

Explanation: Leaving surface.

---

70. What is sign of flux for inward field lines?

Answer: Negative

Explanation: Entering surface.

---

🔹 71–85 (Field & Symmetry)

71. What is condition to apply Gauss law easily?

Answer: Symmetry

Explanation: Simplifies calculation.

---

72. What type of symmetry needed?

Answer: Spherical, cylindrical, planar

Explanation: Common cases.

---

73. What is electric field inside cavity of conductor?

Answer: Zero

Explanation: Shielding effect.

---

74. What is flux through any closed surface?

Answer: Depends on enclosed charge

Explanation: Gauss law.

---

75. What is electric field inside solid conductor?

Answer: Zero

Explanation: Electrostatic equilibrium.

---

76. What happens to charges in conductor?

Answer: Move to surface

Explanation: Repulsion.

---

77. What is electric field at sharp edges?

Answer: Very high

Explanation: Charge concentration.

---

78. What is flux relation with field lines?

Answer: Proportional

Explanation: More lines → more flux.

---

79. What is electric field direction at surface?

Answer: Normal

Explanation: Perpendicular.

---

80. What is flux if equal lines enter and leave?

Answer: Zero

Explanation: Cancel out.

---

81. What is electric field inside charged shell?

Answer: Zero

Explanation: Symmetry.

---

82. What is electric field outside shell?

Answer: Like point charge

Explanation: From center.

---

83. What is flux through curved surface?

Answer: Depends on angle

Explanation: Orientation matters.

---

84. What is electric field due to charge distribution?

Answer: Depends on symmetry

Explanation: Shape matters.

---

85. What is flux additive property?

Answer: Yes

Explanation: Sum of contributions.

---

🔹 86–100 (Advanced Understanding)

86. What is differential form of Gauss law?

Answer:

$\mathrm{\nabla }\cdot E=\frac{\rho }{{\epsilon }_0}$

---

87. What is divergence of electric field?

Answer: Measure of field source

Explanation: Related to charge density.

---

88. What is volume charge density symbol?

Answer: 

$\rho$

Explanation: Charge per volume.

---

89. What is flux through small area?

Answer: 

$d\mathrm{\Phi }=EdA\cos \theta$

Explanation: Differential form.

---

90. What is Gauss law integral form?

Answer:

$$$$∮E⋅dA=Qε0

∮E⋅dA=

ε

0​

Q​

Explanation: Total flux.

---

91. What is field due to uniform sphere inside?

Answer: Varies with radius

Explanation: Not zero.

---

92. What is field at center of sphere?

Answer: Zero

Explanation: Symmetry.

---

93. What is flux for point charge at center?

Answer: Same for all surfaces

Explanation: Shape independent.

---

94. What is electric field at boundary?

Answer: Discontinuous

Explanation: Changes across surface.

---

95. What is tangential component of field at boundary?

Answer: Continuous

Explanation: Does not change.

---

96. What is normal component of field at boundary?

Answer: Discontinuous

Explanation: Depends on charge.

---

97. What is electric field lines nature?

Answer: Continuous

Explanation: Do not break.

---

98. What is flux through cube face (charge at center)?

Answer: Equal on all faces

Explanation: Symmetry.

---

99. What is flux per face of cube?

Answer: 

$\frac{Q}{6{\epsilon }_0}$

Explanation: Total divided equally.

---

100. What is summary of Gauss’s Law?

Answer: Flux depends only on enclosed charge

Explanation: Fundamental electrostatic principle.

101. What is electric flux through a closed surface?

Answer: Depends only on enclosed charge

Explanation: Independent of shape.

---

102. What is Gauss’s law in integral form?

Answer:

$\oint \vec{E}\cdot d\vec{A}=\frac{Q}{{\epsilon }_0}$

---

103. What is divergence of electric field?

Answer: Measure of source of field

Explanation: Related to charge density.

---

104. What is Gauss’s law in differential form?

Answer:

$\mathrm{\nabla }\cdot E=\frac{\rho }{{\epsilon }_0}$

---

105. What is volume charge density?

Answer: Charge per unit volume

Explanation: Represented by 

$\rho$

---

106. What is surface charge density symbol?

Answer: 

$\sigma$

Explanation: Charge per unit area.

---

107. What is linear charge density symbol?

Answer: 

$\lambda$

Explanation: Charge per unit length.

---

108. What is electric flux through open surface?

Answer: Depends on orientation

Explanation: Not fixed.

---

109. What is net flux through closed surface always?

Answer: Enclosed charge / ε₀

Explanation: Gauss law.

---

110. What is flux through surface if E = 0?

Answer: Zero

Explanation: No field.

---

111. What is field inside cavity (no charge)?

Answer: Zero

Explanation: Shielding.

---

112. What is field inside cavity (with charge)?

Answer: Non-zero

Explanation: Due to internal charge.

---

113. What is electric field symmetry required for Gauss law?

Answer: High symmetry

Explanation: Simplifies calculations.

---

114. What is flux through cube enclosing charge Q?

Answer: 

$Q\mathrm{/}{\epsilon }_0$

Explanation: Shape independent.

---

115. What is flux per face of cube (charge at center)?

Answer: 

$Q\mathrm{/}6{\epsilon }_0$

Explanation: Equal distribution.

---

116. What is electric field inside uniformly charged sphere?

Answer: Varies with radius

Explanation: Not constant.

---

117. What is electric field at center of sphere?

Answer: Zero

Explanation: Symmetry.

---

118. What is electric field outside uniformly charged sphere?

Answer: Like point charge

Explanation: Radial field.

---

119. What is flux through sphere due to external charge?

Answer: Zero

Explanation: Not enclosed.

---

120. What is electric field at boundary of conductor?

Answer: Discontinuous (normal component)

Explanation: Due to surface charge.

---

🔹 121–135 (Application & Properties)

121. What is tangential component of electric field at boundary?

Answer: Continuous

Explanation: Does not change.

---

122. What is normal component of electric field at boundary?

Answer: Discontinuous

Explanation: Depends on surface charge.

---

123. What is electric field due to infinite line charge formula?

Answer:

$$$$E=λ2πε0r

E=

2πε

0​

r

λ​

Explanation: Cylindrical symmetry.

---

124. What is electric field due to infinite plane sheet formula?

Answer:

$$$$E=σ2ε0

E=

2ε

0​

σ​

Explanation: Constant field.

---

125. What is flux through hemisphere?

Answer: Half of total sphere flux

Explanation: Symmetry.

---

126. What is Gaussian surface choice based on?

Answer: Symmetry

Explanation: Simplifies integration.

---

127. What is electric field inside conductor in electrostatics?

Answer: Zero

Explanation: Charges rearrange.

---

128. Where does excess charge reside in conductor?

Answer: On surface

Explanation: Repulsion effect.

---

129. What is electric field at sharp edges?

Answer: Very high

Explanation: Charge concentration.

---

130. What is flux through any closed surface?

Answer: Independent of surface shape

Explanation: Depends only on charge.

---

131. What is electric field lines density indicate?

Answer: Field strength

Explanation: Denser → stronger.

---

132. What is electric field direction at surface?

Answer: Normal

Explanation: Perpendicular.

---

133. What is flux if equal lines enter and leave?

Answer: Zero

Explanation: Cancel out.

---

134. What is Gauss law useful for?

Answer: Calculating electric field

Explanation: For symmetric systems.

---

135. What is flux sign convention?

Answer: Outward positive

Explanation: Standard rule.

---

🔹 136–150 (Quick Revision Q&A)

136. Flux depends on?

Answer: Enclosed charge

Explanation: From Gauss law.

---

137. Flux unit?

Answer: 

$N{m}^2\mathrm{/}C$

Explanation: SI unit.

---

138. Electric field inside conductor?

Answer: Zero

Explanation: Electrostatic equilibrium.

---

139. Electric field outside conductor?

Answer: Non-zero

Explanation: Due to surface charge.

---

140. Gaussian surface nature?

Answer: Imaginary closed surface

Explanation: Mathematical tool.

---

141. Flux through cube?

Answer: Same as sphere

Explanation: Shape independent.

---

142. Field inside hollow sphere?

Answer: Zero

Explanation: No enclosed charge.

---

143. Field outside sphere?

Answer: Like point charge

Explanation: Radial.

---

144. Flux through plane?

Answer: Depends on angle

Explanation: Orientation.

---

145. Field symmetry types?

Answer: Spherical, cylindrical, planar

Explanation: Common symmetries.

---

146. Electric field lines?

Answer: Continuous

Explanation: Do not break.

---

147. Field lines start from?

Answer: Positive charge

Explanation: Originate outward.

---

148. Field lines end at?

Answer: Negative charge

Explanation: Terminate inward.

---

149. Field direction?

Answer: Tangent to field line

Explanation: Direction indicator.

---

150. Final summary of Gauss’s Law?

Answer: Flux depends only on enclosed charge

Explanation: Core principle.

151. What is flux through a closed surface enclosing charge Q?

Answer:

$$$$Φ=Qε0

Φ=

ε

0​

Q​

Explanation: From Gauss’s law.

---

152. What is flux through closed surface if no charge is inside?

Answer: Zero

Explanation: No enclosed charge.

---

153. What is flux through surface if charge is outside?

Answer: Zero

Explanation: Only enclosed charge matters.

---

154. What is electric field inside conductor?

Answer: Zero

Explanation: Charges rearrange.

---

155. What is electric field at conductor surface?

Answer: Perpendicular

Explanation: No tangential component.

---

156. What is Gaussian surface?

Answer: Imaginary closed surface

Explanation: Used in Gauss law.

---

157. What is field due to spherical charge outside?

Answer: Like point charge

Explanation: Radial symmetry.

---

158. What is field inside hollow sphere?

Answer: Zero

Explanation: No enclosed charge.

---

159. What is electric field inside uniformly charged sphere?

Answer: Varies with radius

Explanation: Not constant.

---

160. What is flux through cube enclosing charge?

Answer: Same as any surface

Explanation: Shape independent.

---

161. What is flux per face of cube (charge at center)?

Answer: 

$\frac{Q}{6{\epsilon }_0}$

Explanation: Equal distribution.

---

162. What is electric field direction at surface?

Answer: Normal

Explanation: Perpendicular.

---

163. What is flux sign for outward field?

Answer: Positive

Explanation: Leaving surface.

---

164. What is flux sign for inward field?

Answer: Negative

Explanation: Entering surface.

---

165. What is field inside cavity without charge?

Answer: Zero

Explanation: Shielding.

---

166. What is field inside cavity with charge?

Answer: Non-zero

Explanation: Due to internal charge.

---

167. What is Gauss law used for?

Answer: Calculating electric field

Explanation: Especially symmetric systems.

---

168. What is required for easy Gauss law application?

Answer: Symmetry

Explanation: Simplifies math.

---

169. What is electric field lines relation to flux?

Answer: Proportional

Explanation: More lines → more flux.

---

170. What is electric field at sharp edges?

Answer: Very high

Explanation: Charge concentration.

---

🔹 171–185 (Advanced Concepts)

171. What is electric field inside solid conductor?

Answer: Zero

Explanation: Electrostatic equilibrium.

---

172. Where does excess charge reside?

Answer: On surface

Explanation: Due to repulsion.

---

173. What is flux independent of?

Answer: Surface shape

Explanation: Only charge matters.

---

174. What is flux dependent on?

Answer: Enclosed charge

Explanation: Gauss law.

---

175. What is electric field direction for sphere?

Answer: Radial

Explanation: Symmetry.

---

176. What is Gaussian surface for plane sheet?

Answer: Pillbox

Explanation: Planar symmetry.

---

177. What is Gaussian surface for line charge?

Answer: Cylinder

Explanation: Cylindrical symmetry.

---

178. What is Gaussian surface for spherical charge?

Answer: Sphere

Explanation: Radial symmetry.

---

179. What is electric field due to infinite plane sheet?

Answer: Constant

Explanation: Independent of distance.

---

180. What is electric field due to line charge?

Answer: Decreases with distance

Explanation: 

$\propto \frac{1}{r}$

---

181. What is flux through hemisphere?

Answer: Half of sphere

Explanation: Symmetry.

---

182. What is electric field inside charged shell?

Answer: Zero

Explanation: No enclosed charge.

---

183. What is electric field outside shell?

Answer: Like point charge

Explanation: From center.

---

184. What is electric field discontinuity at surface?

Answer: Normal component changes

Explanation: Due to surface charge.

---

185. What is tangential component of field at boundary?

Answer: Continuous

Explanation: Does not change.

---

🔹 186–200 (Quick Revision)

186. What is normal component of electric field at boundary?

Answer: Discontinuous

Explanation: Depends on charge.

---

187. What is flux unit?

Answer: 

$N{m}^2\mathrm{/}C$

Explanation: SI unit.

---

188. What is electric field inside conductor?

Answer: Zero

Explanation: Charges cancel field.

---

189. What is electric field outside conductor?

Answer: Non-zero

Explanation: Due to surface charge.

---

190. What is flux through any closed surface?

Answer: 

$Q\mathrm{/}{\epsilon }_0$

Explanation: Gauss law.

---

191. What is electric field lines nature?

Answer: Continuous

Explanation: Do not break.

---

192. What is electric field lines start from?

Answer: Positive charge

Explanation: Originate outward.

---

193. What is electric field lines end at?

Answer: Negative charge

Explanation: Terminate inward.

---

194. What is field direction?

Answer: Tangent to field line

Explanation: Shows direction.

---

195. What is flux for uniform field?

Answer: Easy to calculate

Explanation: Constant field.

---

196. What is flux if θ = 0°?

Answer: Maximum

Explanation: Cos 0 = 1.

---

197. What is flux if θ = 90°?

Answer: Zero

Explanation: Cos 90 = 0.

---

198. What is Gauss law importance?

Answer: Simplifies field calculation

Explanation: Powerful tool.

---

199. What is flux additive?

Answer: Yes

Explanation: Sum of contributions.

---

200. What is final summary of Gauss’s Law?

Answer: Electric flux through closed surface depends only on enclosed charge

Explanation: Fundamental electrostatic principle.