How is permittivity of free space experimental value obtained?
Answers
The purpose of this experiment was to determine a value for the permittivity of free space. This was done by measuring the force between a charged sphere and an earthed metal plate. We obtained a value for the permittivity of free space of 12.0±0.8×10?12 Fm?1 which is in disagreement with the accepted value 8.854187 817. ..×10?12 Fm?1 . Likely causes for this were random errors in the force meter.
1. Introduction The permittivity of free space ?0 , also known as the electric constant, is a fundamental constant of physics. It describes how electric fields behave in a vacuum and therefore how charges interact in a vacuum. The value of ?0 is known to be exactly [1] 8.854187 817. ..×10?12 Fm?1 . This value is known to be exact because the constant can be expressed in terms of the magnetic constant ?0 and the speed of light c. Despite this, accurately measuring the electric constant is still important because it allows for the confirmation of theory by comparison of theoretical and experimental determinations of the constant. In our experiment a conducting sphere was charged and placed in a force meter, a metal plate acting as another charge was then introduced. The force was recorded, for different separations, and this was used to calculate ?0 . A similar set up could be used to calibrate a force meter as the force between sphere and plate is easily calculable. By adjusting a force meter so that it agreed exactly with the calculated value, a meter can be calibrated. Calibration of instruments is important for precision experiments and, therefore, methods for calibration are vital.