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If the charge on a spherical conductor of radius R is Q, then electric field at distance r from centre is E = 0 (if r < R) or E = Q / (4πε₀r²) (if r ≥ R). Electric field at a distance 15 cm from the centre of sphere will be:

1. E = 9 × 10⁹ × 3.2 × 10⁻⁷ / 225 × 10⁻⁴
2. E = 0.128 × 10⁶ = 1.28 × 10⁵ N/C
3. E = Q / (4πε₀r²)
4. None of the above

Correct answer: E = 9 × 10⁹ × 3.2 × 10⁻⁷ / 225 × 10⁻⁴

Solution

The electric field outside a spherical conductor is given by E = Q / (4πε₀r²). Substituting the given values into the formula, the result matches option A.

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