Practice portal › Electric Charge and Properties › Electric Field of Point Charges

A charge Q is placed on each of (n-1) corners of a regular polygon of n sides. The distance of each corner from the centre of the polygon is r. The electric field at its centre is …..

Asked in RS Academy GUJCET booklet · Field of discrete charges

• (1) (kQ)/(r²)
• (2) (n-1)(kQ)/(r²)
• (3) n/(n-1) (kQ)/(r²)
• (4) (n-1)/n (kQ)/(r²)

Step-by-step solution

Why the other options are wrong

• (2) This adds the magnitudes of the (n-1) fields as if they all pointed the same way. They point in different directions round the polygon and almost all cancel.
• (3) No single physical route gives this factor. Sanity check: for a square (n = 4) with three charges, the two opposite charges cancel and the third leaves exactly (kQ)/(r²), not 4/3 (kQ)/(r²).
• (4) No single physical route gives this factor. Sanity check: for a square (n = 4) with three charges, one charge is left unpaired, so the field is (kQ)/(r²), not 3/4 (kQ)/(r²).

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.