30 Jun, 2013
Of a current
PRESENTATION: A conductive thread is set aligned on a small magnet in line with the earth’s magnetic field in turn. When the electric current flows, the magnet changes its orientation due to the superposition of the magnetic field of its perpendicular current with the earth’s magnetic field already present. This orientation changes when the current flows in the opposite direction.
- F = qv×B:v is with Respect to What?, Kent W. Scheller and, Thomas J. Pickett, Phys. Teach. 51, 169 (2013)
- A New Direction: How a Compass Pointed the Way to Clearing Up an Attractive Misconception , Tracy Hood, Phys. Teach. 50, 398 (2012)
INTRODUCTION: the discovery of the existence of a force between charges in movement and magnets was accidentally made by Hans Christian Oersted in 1820, a Danish professor of Physics. At the end of a class she tried to show there was no relation between electricity and magnetism by means of a current that passed by a magnetized needle. In the words of one of his disciples “he was perplexed when he saw that the needle showed a large oscillation.”
OBJECTIVE: to check that the electric current creates a magnetic field around it.
MATERIALS: a battery, red wire, 2 red connecting clamps, 2 black connecting clamps, a compass.
SETUP: each end of each cable is connected with a clamp of the same colour: black clamp for the black wire and red clamp for the red wire. The cables are attached to the battery, the black to the negative pole and the red to the positive pole, and the cables are connected together by their free ends. Finally, the cables are passed over the compass at a short distance. If it is the red cable, the compass turns towards one side and if it is the black it turns to the other.
EXPLANATION: Creating a simple circuit with a generator (battery) and some cables linking both poles, the electric current that flows through them creates in its movement a magnetic field that acts on a compass when approached, provoking a magnetic force which orients the magnet in the direction of the total magnetic field (the one created by the current and the earth’s). With this experience, Oersted related electricity with magnetism for the first time.
CONCEPTS: magnetic field, magnetic force, electric current, magnetism, magnet.
- Tipler P.A. Física, Reverté, 2010.
- De Juana J.M., Física General, Pearson, 2009.
- Serway R.A, Jewett J.W., Física, Thomson-Paraninfo, 2010.
- Teplitz D., Electromagnetism. Paths to research, Plenum Press, 1982.
- Cheng D.K., Fundamentos de electromagnetismo para ingeniería, Alhambra Mexicana, 1998.
STUDENTS 2012-2013: Adrián Cancela, Adrián Carpintero, Bernardo Cendán, Pedro Pérez
LINK pdf STUDENTS (in Spanish):