A physics team measures the magnitude of the electric field surrounding an unknown

PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

A physics team measures the magnitude of the electric field surrounding an unknown, isolated spherical object. The measurements, taken along a radial line extending outward from the center of the object, are shown in the table below.

Radial distance $r$ (m)	0.20	0.30	0.40
Measured $E$ (N/C)	$2.25 \times 10^4$	$1.00 \times 10^4$	$5.63 \times 10^3$

Additional measurements reveal that within a distance of

0.10\,\text{m}

from the center, the magnitude of the electric field is essentially zero everywhere. (a) Using only the numerical data in the table, determine whether the object’s external field is consistent with that of a point charge. Support your reasoning quantitatively. (b) Assuming consistency with a point charge, calculate the net charge of the object. (c) Based on the observation that the field inside

r = 0.10\,\text{m}

is approximately zero, decide whether the object is most likely a solid conducting sphere or a solid insulating sphere. Explain your reasoning. (d) Identify one plausible experimental source of error that could cause small deviations from the ideal mathematical relationship you analyzed in part (a), and describe its effect on the measured values.

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