MCQ based on Electric Flux for NEET

Q.1. The number of electric lines of force that radiate outwards from one coulomb of charge in vacuum is
(a) 1.13 × 1011
(b) 1.13 × 1010
(c) 0.61 × 1011
(d) 0.61 × 109

Answer Answer: (a) Φ = q/ε0 = 1.13 × 1011

Q.2. If the electric flux entering and leaving an enclosed surface respectively is Φ1 and Φ2, the electric charge inside the surface will be
(a) (Φ2 + Φ2) × εo 
(b) (Φ2 – Φ2) × εo
(c) (Φ1 + Φ2) × εo 
(d) (Φ2 – Φ1) × εo

Answer Answer: (d)

Q.3. A cylinder of radius R and length L is placed in a uniform electric field E parallel to the axis of the cylinder. The total flux over the curved surface of the cylinder is
(a) zero
(b) πR2E
(c) 2πR2E
(d) E / πR2

Answer Answer: (a)

Q.4. In a region of space having a uniform electric field E, a hemispherical bowl of radius r is placed. The electric flux Φ through the bowl is
(a) 2πRE
(b) 4πR2E
(c) 2πR2E
(d) πR2E

Answer Answer: (c)

Q.5. At the centre of a cubical box + Q charge is placed. The value of total flux that is coming out a wall is
(a) Q / εo 
(b) Q / 3εo 
(c) Q / 4εo  
(d) Q / 6εo

Answer Answer: (d)

Q.6. A charge Q is enclosed by a Gaussian spherical surface of radius R. If the radius is doubled, then the outward electric flux will
(a) increase four times
(b) be reduced to half
(c) remain the same
(d) be doubled

Answer Answer: (c)

Q.7. A charge q is placed at the centre of the open end of a cylindrical vessel. The flux of the electric field through the surface of the vessel is
(a) Q / εo 
(b) Q / 2εo 
(c) Q / 4εo  
(d) zero

Answer Answer: (b)

Q.8. Which of the following graphs correctly show the change of electric flux Φ with time t through the surface S when the charge +Q is moved away from the surface?

Answer Answer: (c) Since electric field due to a point charge is inversely proportional to the square of distance therefore the field decreases at the place of surface S as the charge + Q moves away. Therefore the flux given by Φ=ES cosθ also decreases.

Q.9. In the figure the net electric flux through the area A is Φ=ES cosθ when the system is in air. On immersing the system in water the net electric flux through the area

(a) becomes zero
(b) remains same
(c) increases
(d) decreases

Answer Answer: (d)

Q.10. An electric dipole is placed at the centre of a sphere then
(a) the flux of the electric field through the sphere is not zero.
(b) the electric field is zero at every point of the sphere.
(c) the electric field is not zero anywhere on the sphere.
(d) the electric field is zero on a circle on the sphere.

Answer Answer: (c)

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