新加坡初二科学物理.doc

,Name S.I unit Symbol Current ( I) Amphere A Voltage (V ) Volts V Resistance (R ) Ohms ? Electric Energy ( E) Joule J Power ( P) Watt W Amount of charge ( Q) Coulomb C Component Symbol Component Symbol Cell Fuse Batteries Ammeter Light bulb Voltmeter Open switch Closed switch Resistor Variable resistor Open circuit Closed circuit ~ called incomplete ~no electricity flows in the circuit ~may caused by faulty working devices or a break in the protective devices ~ called a complete circuit ~the switch is closed hence the circuit is complete ~electricity flows continuously Category What is it? Example Uses in electricity Conductors Materials that allow electricity to pass through them easily Copper Silver Other metals Copper is used as the conducting wire. Insulators Materials that do not allow electricity to pass through them Plastic Rubber Glass Fibres Wood Plastic or rubber is used as protective layers on the wires. Resistors Materials that limit or regulate the amount of electricity passing through them. Convert electrical energy into other forms of energy. Nichrome which is made o nickel and chromium. Nichrome is used as the heating element to convert electrical energy into heat energy. Series Circuit Parallel Circuit ~The loads are arranged one after one in a single loop or branch. ~There is only one path for electricity to flow through. ~The advantage of a series circuit is it is simple to build. ~A series circuit has two disadvantages: - When more loads are added, the total resistance in the circuit increases. - When one load is damaged, it affects the functionality of the other loads. ~The loads are arranged in multiple loops or branches. ~There are more than one path for electricity to flow through. ~A parallel circuit has two advantages: - When more loops are added, the total resistance in the circuit decreases. - When one load is damaged, it does not affect the functionality of the other loops. Cu