Intelligent assessment and revision tools for OCR A Physics

A student investigates whether the electrical power P delivered to a small heater is proportional to the square of the current I through it. They obtain two readings: at I = 0.40 A, P = 1.9 W; at I = 0.80 A, P = 7.6 W. Without using logs, which statement must be true when using a straight-line test to assess this model and estimate the constant?

• A Plot P against I; expect a straight line through the origin; doubling I should double P; using I = 0.40 A gives a gradient about 4.8 W A^-1.
• B Plot P against I^2; expect a straight line through the origin; doubling I should roughly quadruple P; using I = 0.40 A gives a gradient about 12 W A^-2.
• C Plot I^2 against P; expect a straight line through the origin; using I = 0.40 A gives a gradient about 12 and this equals the resistance.
• D Plot P against 1/I; expect a straight line; using I = 0.80 A gives a gradient about 6.1 in units of W·A.