Data: r1 (first specified distance from the charge) = 7 cm; E1 (value of the field strength at a distance r1) = 3 N / C; r2 (second given distance from the charge) = 11 cm.
The field strength at a distance of 11 cm from the charge is determined from the ratio: E1 * r1 ^ 2 / k = q = E2 * r2 ^ 2 / k, whence E2 = E1 * r1 ^ 2 / r2 ^ 2.
Calculation: E2 = 3 * 7 ^ 2/11 ^ 2 = 1.21 N / C.
Answer: At a distance of 11 centimeters from the charge, the field strength is 1.21 N / C.
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