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# Verify coulomb's law.

Extracts from this document...

Introduction

## Coulomb’s law lab

Objective: to verify coulomb’s law

Materials:

String

Wool cloth

Plastic ruler

Box

2 Graphite balls, one attached to the string

Procedures:

1. measure the mass of the graphite ball which is attached to the string
2. put the ball in the box with the string attached with the box, measure the distance from the top of the box where the string is attached, to the hanging ball, also measure the horizontal position of the ball
3. rub the ruler with the wool cloth so that it is charged
4. use the ruler to touch the other ball which is attached to a holding tool, so it gets charged
5. place the charged ball into the box, until that it touches the ball in the box
6. the balls will then repel, record the distance of the repulsion, the distance is measured from the center of the ball to the center of the other ball
7. To record the distance, one sees the scale through the transparent glass, and should not see the image of the ball in the mirror

Middle

 trial # equilibrium position of the hanging ball(m) position of the hanging ball after repulsion the change distance(x) 1 0.043 0.033 0.01 2 0.043 0.035 0.008 3 0.043 0.032 0.011 4 0.043 0.035 0.008 5 0.043 0.028 0.015

Table 3 tanθ using =x/L

 trial # (x)the change in distance of the hanging ball(m) (L)length of the imaginary string(m) tanθ 1 0.01 0.217 0.046 2 0.008 0.217 0.037 3 0.011 0.217 0.051 4 0.008 0.217 0.037 5 0.015 0.217 0.069

Weight of the ball(Mg) is calculated by the hanging ball’s mass multiplied by g:

=1.1x10^-4kg* 9.8

=0.001078N

Conclusion

θ may not be exactly precise, because we are assuming x is at right angle with L.

Suggestions for improvement

The loss of charges in the experiment cannot be prevented, but a suggestion is to do it on a dry day, where the charges would not escape into the air as in a humid day would. The approximation of x can be much improved by opening the lid of the box and hang the string from the ceiling. This way, the L would be much larger, and the approximation of tanθ would be more precise because now is at a smaller angle.

Conclusion

The experiment fairly showed the columb’s law, and the relationship between the variables, r, fe, q. During the process, as the charges are lost to the air, the distance as well as fe decreased. The graph of fe vs 1/(r^2) suggested a straight line, a linear relationship between the two variables, that the force between the two charges was inversely proportional to the square of the distance between them r2.

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