Caroline Chisholm College Physics

1. n-type n-type p-type p-type ELECTRON CURRENT CONVENTIONAL CURRENT • In an appliance, we may need to: • control current flow direction • convert AC to DC • turn current on or off • amplify a current Caroline Chisholm College Physics Describe differences betweensolid state and thermionicdevices and discuss why solidstate devices replacedthermionic devices These tasks used to be done by THERMIONIC DEVICES ( VALVES ) Now they are done by SOLID STATE DEVICES (e.g. TRANSISTORS - solid state diodes) These used heated filaments and terminals in glass vacuum tubes. The filament liberates electrons, which are accelerated to the anode by high voltage. There is no heating of the anode, so the current will not reverse (i.e. UNIDIRECTIONAL) Solid state diodes are made from semiconductor materials. e.g. junction between p-type (hole) and n-type (electron) acts as a diode. Electron flow is always from n-type to p-type. i.e. UNIDIRECTIONAL e.g. thermionic diode A grid (third electrode) can act as a current amplifier. Variations in the grid current produce larger variations in the anode current. e.g. In a valve radio, after the carrier signal is removed, a smaller signal (the music etc.) remains, which can be amplified by the valve. Donor Acceptor REVERSE BIAS FORWARD BIAS Current DOES NOT flow easily/at all Current flows easily

2. Caroline Chisholm College Physics Describe differences between solid state and thermionic devices and discuss why solid state devices replaced thermionic devices SOLID STATE DEVICES ARE MORE EFFICIENT, LESS COSTLY AND MORE RELIABLE! They have fewer connections, less wiring, less heat produced and faster signal processing. Gather, process and present secondary information to discuss how shortcomings in available communication technology lead to an increased knowledge of the properties of materials with particular reference to the invention of the transistor Problems with thermionic devices: BULKY GENERATED HEAT FRAGILE These problems prompted scientists to look to new materials to perform the functions of thermionic devices CATHODE COATING DETERIORATED SHORT LIFETIME HIGH VOLTAGES REQUIRED

3. Caroline Chisholm College Physics

4. A transistor is a tiny switch that changes the size or direction of electric current as a result of very small changes in the voltage across it. Caroline Chisholm College Physics Identify data sources, gather,process, analyse informationand use available evidence toassess the impact of theinvention of transistors onsociety with particular referenceto their use in microchips andmicroprocessors They are used in sound amplifiers and a wide range of electronic devices. A single microchip of silicon can hold many (even millions of) microscopic transistors and is called an integrated circuit IC's made miniaturization of electronic circuits possible The advantages of transistors meant computers ran much faster and could handle incredible amounts of data. Intel produced its first microprocessor in 1971. Cheaper, smaller, tabletop and hand-held computers make this processing power available to all sizes of businesses, educational institutions and homes, impacting on society’s productivity, access to information and capability to process increasingly complex data. Large scale integration (LSI) has produced powerful hand-held calculators and ICs allowed complete appliances to be built onto a single microprocessor chip. There have also been positive impacts on our communication (mobile phones use microchips), business, travel, shopping and entertainment, all of which use microchips now. Silicon transistors are also used in solar cells, which provides the benefit of a clean energy resource. It may also be argued that transistors adversely affected society by introducing technology (computers, games etc. that distract people from healthier pursuits such as exercise, have reduced our personal contact and introduced a volume of data that has unneccesarily increased the complexity of our world.