Effect of Material
Effect of Material Substances, which allow electric current to flow through them, are called conductors. Those, which do not, are called insulators. Metals behave as conductors because of their structure. In a metal structure the metal atoms release their outermost electrons to form an "electron cloud" throughout the whole structure. In other words the atoms in a metal exist as ions surrounded by an electron cloud. If a potential difference is applied to the metal the electrons in this cloud are able to move. Some conductors are better than others. Copper is a conductor than iron. When the electrons are moving through the metal structure they bump into the metal ions and this causes resistance to the electron flow or current. In different conductors the ease of flow of the electrons is different and so the conductors have different resistance. For a particular conductor the resistance will depend on its length and cross-sectional area. The longer the conductor, the further the electrons have to travel, the more likely they are to have collisions with the metal ions and so the greater the proportional to length. The greater the cross-sectional area of the conductor, the more electrons available to carry the charge along the conductor's length and so lower the resistance. Resistance is inversely proportional to cross-section
Description of an Electric Bell
Many objects around us contain electromagnets. They can be found in electric motors and loudspeakers. Powerful electromagnets are used as lifting magnets in scrap yards. Another use an electromagnet is an electric bell used in most schools. When the switch is turned on, the current flows through the circuit and the electromagnet makes a magnetic field, therefore the electromagnet then attracts the striker (metal arm) which then hits the bell, however because the striker has moved the contact is broken and the circuit is broken[m1] between the striker's contact and the other contact,the striker moves back, and the circuit is complete again and the cycle repeats again and again until the switch is turned off. This how an electric bell works. This is an OK explanation and I appreciate the inclusion of the diagram. It needs that one modification. [m1]Where is the circuit broken? Use of an Electromagnet Sourouthi Navalan
Investigation: How length affects the resistance in a wire.
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