What is the electric flux through a cube with a charge at its centre?

By Gauss's law it's q/ε₀ total, split equally as q/6ε₀ through each of the 6 faces — kyunki sab faces symmetric hain.

Why is the flux only q/8ε₀ when the charge is at a corner of the cube?

A corner is shared by 8 identical cubes (a 2×2×2 block). The charge can't tell them apart, so each cube — including yours — gets 1/8 of the total q/ε₀.

What is the flux through a cube when the charge is at the centre of one face?

q/2ε₀. The charge sits on the surface, so only half its field lines enter the cube; the other half escape into the opposite half-space.

Does electric flux depend on the position of the charge inside the cube?

No. As long as the charge is fully enclosed, the total flux is always q/ε₀ regardless of where inside it sits — that's the heart of Gauss's law. It only drops when the charge moves onto the surface (face/edge/corner).

What is the flux through one face of a cube when the charge is at a corner?

The 3 faces touching the corner get 0; the 3 far faces share the q/8ε₀ equally → q/24ε₀ per far face. (A common JEE-level follow-up.)

Why is the flux zero through the face that contains the charge?

The field lines from a charge lying on that face are in the plane of the face — they graze it instead of piercing it, so the perpendicular flux through it is zero.

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Electric Flux — Cube

PhysicalMediumNEET: 2-3 Q3D

Electric Flux Through a Cube

Electric Charges and Fields

Move a point charge to the centre, face, edge, and corner of a cube and watch the electric flux change from q/ε₀ to q/8ε₀ — Gauss's law you can rotate and feel, not memorize.

Loading lab

Built by Animesh Singh · @neetlab

Tap to move the charge. Turn on "Complete the enclosure" to see why each spot gives 1/N of q/ε₀.

How to use this lab

1Charge ko Body → Face → Edge → Corner pe move karo (4 buttons).
2Total flux q/ε₀ → q/2ε₀ → q/4ε₀ → q/8ε₀ badalta dekho.
3“Complete the enclosure” dabao — N cubes charge ko gher‌te hain, tumhara cube 1/N.
4Canvas ko drag karke har angle se ghumao.

What you're seeing

Charge ko cube ke andar idhar-udhar ghumao — flux badlega ya nahi? Gauss kehta hai: bas andar ka charge matter karta hai, position nahi. Khud dekho.

Key NEET facts

▸Body centre: q/ε₀ — Pura charge andar — saari field lines cube ko pierce karti hain. 6 faces barabar → q/6ε₀ each.
▸Face centre: q/2ε₀ — Charge surface pe — aadhi lines doosri taraf nikal jaati hain. Jis face pe charge baitha hai, uska flux = 0 (lines us face ko graze karti hain).
▸Edge centre: q/4ε₀ — Ek edge ko 4 identical cubes share karte hain. Tumhara cube unmein se 1 → 1/4 flux.
▸Corner (vertex): q/8ε₀ — Corner pe 8 cubes milte hain (2×2×2 block). Ek cube = 1/8 flux. Sabse famous NEET trap.
▸Golden rule: Φ = q_in/ε₀ — Shape, size ya andar ki exact position — koi fark nahi. Sirf enclosed charge ka fraction count hota hai.

Memory trick

Soch: charge ko poora gherne ke liye kitne cubes chahiye? Body = 1 → q/ε₀. Face = 2 → ÷2. Edge = 4 → ÷4. Corner = 8 → ÷8. Bas yaad rakho 1-2-4-8: "Ek ghar, do padosi, chaar edge pe, aath corner pe."