2.4 Resistance ohmic conductor.pptVIP

We can see from graph that while the resistance of the resistor is constant, that of the light bulb increases with increasing potential, whereas the resistance of the diode decreases with increasing potential. The resistor obeys Ohm’s law, but the others do not. * Other non-ohmic conductors include devices whose resistance changes with light or temperature. These are particularly useful as detectors in sensors that need to respond to changes in light levels or temperature * 吴礼星 Wen Zhou NO.21 middle school 2.4 Resistance, ohmic and non-ohmic conductors The ammeter is used to measure the current flowing in a circuit 1.Ammeters and voltmeters symbol A It would be necessary to connect an ammeter in series (串联) with circuit elements A analogue 指针式的 digital 数字的 1.Ammeters and voltmeters A voltmeter is used to measure the potential difference across any circuit element or source of EMF symbol V It would be necessary to connect a voltmeter in parallel(并联) with circuit elements V Multimeter combine several functions in one meter. Multimeter 万用表 If you have set up a circuit as shown. In which of the positions, shown M1–M4, can you place: a a voltmeter? b an ammeter? M2 or M3 M1 or M4 Problem 1 Never place an ammeter in parallel because it would be a short circuit that could damage the meter, the circuit or both Can an ammeter be connected in parallel with device? Potential difference 2V 4V 6V 8V …… Current 0.1A 0.2A 0.3A 0.4A …… I(A) 0.2 0.4 V (V) 0 2 4 6 8 I–V characteristic （伏安特性） graph Table 1 2.Current–voltage graphs The relationship between the current and the voltage I–V characteristic （伏安特性） Resistor电阻 2.Current–voltage graphs The relationship between the current and the voltage I–V characteristic（伏安特性） light bulb电灯炮 2.Current–voltage graphs The relationship between the current and the voltage I–V characteristic （伏安特性） Diode二级管 Some example of I-V g