Problem 21-40a:
the electric field near the surface of earth points downward and has a magnitude of 153 n/c. what is the ratio of the magnitude of the upward electric force on an electron to the magnitude of gravitational force on the electron?
2.74×1012
problem 21-40b:
what charge should be placed on a plastic ball of mass 5.25 g so that the electric force balances the weight of the ball near earth's surface?

Acommon technique in analysis of scientific data is normalization. the purpose of normalizing data is to eliminate irrelevant constants that can obscure the salient features of the data. the goal of this experiment is to test the hypothesis that the flux of light decreases as the square of the distance from the source. in this case, the absolute value of the voltage measured by the photometer is irrelevant; only the relative value conveys useful information. suppose that in part 2.2.2 of the experiment, students obtain a signal value of 162 mv at a distance of 4 cm and a value of 86 mv at a distance of 5.7 cm. normalize the students' data to the value obtained at 4 cm. (divide the signal value by 162.) then calculate the theoretically expected (normalized) value at 5.7 cm.