The total number of electric field lines passing a given area in a unit time is defined as the electric flux.
If the plane is normal to the flow of the electric field, the total flux is given as:
Ξ¦=EA
When the same plane is tilted at an angle Ζ, the projected area is given as AcosΖ and the total flux through this surface is given as
Ξ¦ = EACosΞΈ
Where,
- E is the magnitude of the electric field
- A is the area of the surface through which the electric flux is to be calculated
- Ζ is the angle made by the plane and the axis parallel to the direction of flow of the electric field
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Q1: What is the value of total flux through the faces of the cube with the sides of length a if a charge Q is placed at corner A of the cube is
- q/Ξ΅0
- q/2Ξ΅0
- q/4Ξ΅0
- q/8Ξ΅0
Answer: (d) q/8Ξ΅0
Q2: If a unit positive charge is kept in the air. Then the total flux coming out of unit charge is
- 4ΟΞ΅0-1
- 4ΟΞ΅0
- Ξ΅0-1
- Ξ΅0
Answer: (c)Ξ΅0-1
Q3: What is the value of electric flux (Ξ¦) on a plane of area 1m2 on which an electric field of 2 V/m crosses with an angle of 300.
- 1 Vm
- 2 Vm
- 3 Vm
- 4 Vm
Answer: (a) 1 Vm
Q4: Determine the electric flux of a flat square having an area of 10m2 is a uniform electric field of 8000 N/C passing perpendicular to it
- 8 x 105 Nm2/C
- 8 x 104 Nm2/C
- 16 x 105 Nm2/C
- 4 x 104 Nm2/C
Answer: (b) 8 x 104 Nm2/C
Q5: A plane surface is rotated in a uniform electric field. When is the flux of the electric field through the surface maximum?
- When the surface is perpendicular to the field
- When the surface is parallel to the field
- When the surface is at an angle of 300 with the field
- When the surface is at an angle of 450 with the field
Answer: (a) When the surface is perpendicular to the field
Q6: When is the flux through a surface taken as positive
- When the flux lines are directed inwards
- When the flux lines are directed outwards
- No flux lines through the surface
- Flux lines are parallel to each other
Answer: (b) When the flux lines are directed outwards
Q7: The net charge through a closed surface in a given medium depends on
- Size of the surface
- Charge of the surface
- The shape of the surface
- Area of the surface
Answer: (b) Charge of the surface
Q8: The dimension of electric flux is
- [M2L2T3A1]
- [MLT-3A-1]
- [M3L3T-3A-1]
- [ML3T -3A-1]
Answer: (d) [ML3T -3A-1]
Q9: The electric flux through a cubical Gaussian surface enclosing net charge q is q/Ξ΅0. While the electric flux through one face of a cube is
- q/Ξ΅0
- q/6Ξ΅0
- q/4ΟΞ΅0
- q/4Ξ΅0
Answer: (b) q/6Ξ΅0
Q10: A point charge q is placed at a distance a/2 directly above the centre of the square of side a. The electric flux through the square is
- q/Ξ΅0
- q/6Ξ΅0
- q/4ΟΞ΅0
- q/4Ξ΅0
Answer: (b) q/6Ξ΅0
Explanation for Q10: Imagine a cube with charge q at the centre and the given square is one of its faces. So electric flux through the given square( one face) q/6Ξ΅0
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