1. In an appliance, we may need to: control current flow direction convert AC to DC turn current on or off amplify a current 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) 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. e.g. thermionic diode 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 n-type p-type Current flows easily ELECTRON CURRENT CONVENTIONAL CURRENT n-type p-type Current DOES NOT flow easily/at all Describe differences between solid state and thermionic devices and discuss why solid state devices replaced thermionic devices

2. 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 They have fewer connections, less wiring, less heat produced and faster signal processing.

4. Identify data sources, gather, process, analyse information and use available evidence to assess the impact of the invention of transistors on society with particular reference to their use in microchips and microprocessors 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. 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 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.