resistence basic guide :: essays research papers

A basic guide to resistance. Electron Flow Model Everything is made of very small particles called atoms. Each atom has a heavy positively charged nucleus and is surrounded by a cloud of light, negatively charged, electrons. In metals, the outer most electron of each atom is weakly attracted to the positive nucleus and can escape from the atom and wander around between the atoms. [Note 1] So, in metals, we have all these millions and millions of electrons whizzing about at high speed, in random directions, between the fixed atoms. When you connect the piece of metal across a battery all these electrons are still whizzing about at random, BUT they are also forced to slowly drift in one direction. This slow drift is called the current. [Note 2] As the electrons are forced through the metal they collide with the atoms and transfer energy to them. This is where the word resistance comes in. The electrons experience resistance to their forced movement between the atoms. When the electrons collide with the atoms the electrons lose energy and slow down, the atoms gain energy and vibrate faster. You should know that the faster the vibration of particles the hotter the temperature of the material is. So the energy from the battery, that is used to force the electrons to move, is transferred to the atoms, and we see this as the metal getting hotter. The resistance of a metal always leads to a heating effect when a current is passed through it. The size of the resistance will depend on the type of metal, and its dimensions. Note 1 The regular arrangement of atoms in metals is called the "lattice" or "crystal lattice". The electrons are not completely free from the nuclei so it is not quite correct to describe the electrons as "free electrons" or the atoms as "positive ions". However, in many books you will see metals described as "a sea of electrons moving randomly through a lattice of positive ions." In newer books and your GCSE specification you might find the atom parts described as "positive atomic kernels". Anyway, this whole arrangement is known as "metal bonding" and the attraction of the electrons to the positive atomic kernels produces the characteristic properties of metals. Note 2 The current in a metal is due to the drift of electrons. Without the atomic model many people get the idea that charges (electrons) flow out of one end of a battery, through the wire, and then back in to the other end of the battery.