Intelligent assessment and revision tools for OCR A Physics

In a lab, a student measures the electric field strength E at various distances r from the centre of a small isolated charged sphere. They want to test whether E follows an inverse‑square dependence on r (assume no background field). Which statement must be true if that model is correct?

• A Plot E against r to get a straight line through the origin; doubling r would reduce E to half.
• B Plot E against 1/r to get a straight line through the origin; increasing r by a factor of 1.5 would reduce E to about 0.67 of its value.
• C Plot E against 1/r² to get a straight line through the origin with gradient equal to the constant of proportionality; increasing r by a factor of 1.5 would reduce E to about 0.44 of its value.
• D Plot 1/E against r² to get a straight line through the origin with gradient equal to the constant of proportionality; doubling r would reduce E to half.