30 Jun, 2013
PRESENTATION: Electrically neutral matter has the same number of protons and electrons and can be charged when rubbing it with another object and there is electron transfer. In this case another more electroaffinitive material will obtain a negative charge because it attracts electrons towards itself while a less electroaffinitive material will obtain a positive charge because it yields electrons.
- Roll over, Rover, Mike Shaw, Phys. Teach. 49, 248 (2011)
- Electrostatics with Computer-Interfaced Charge Sensors, Robert A. Morse, Phys. Teach. 44, 498 (2006)
INTRODUCTION: The electric charge is a physical property of some subatomic particles which manifests itself by means of forces of attraction or and repulsion among them. The electrically charged matter is influenced by the electromagnetic fields, being at the same time their generator. The so-called electromagnetic interaction between charge and electric field is one of the four fundamental interactions of Physics. From the perspective of the standard model, the electric charge is the capacity of the measure a particle possesses for the exchange of electrons.
OBJECTIVE: To check the behaviour of two charged spheres when a negative charge approaches them.
MATERIALS: two ping pong balls covered with aluminum foil, cord, balloon, holders, piece of wool.
SETUP: We cover the balls with aluminum foil and we hang them from the holder so there is contact between them. We charge the balloon negatively rubbing it with the piece of wool and we approach it to one of the balls. Then a repulsion can be observed, provoked by the negative particles of the sphere. This first sphere is charged positively and the second negatively.
EXPLANATION: when the balloon is rubbed with the piece of wool it charges negatively. When it is approached to the first of the spheres (with neuter charge) the charges are distributed between the two spheres and the one in contact with the balloon is charged positively and the other negatively. The negative charge of the balloon makes one sphere be totally charged in positive and the other totally in negative.
CONCEPTS: electrostatic charge, charging by induction, polarization charge.
- R. Serway, Física, Mac Graw Hill, 2010.
- P. Tipler, Física para la Ciencia y la tecnología, Reverté, 2012.
- F.W. Sears, M.W. Zemansky, H.D. Young, R.A. Fredman, Física Universitaria, Pearson, 2010.
STUDENTS 2012-2013: Sergio Martínez, Manuel Ribá, Luis Rodríguez, Noela Rama
LINK pdf STUDENTS (in Spanish):