2Learning ObjectivesTo recall the symbols for different circuit components.To investigate the characteristics of different components.Draw and explain the characteristics for a wire, a filament bulb, thermistor and diode.Explain how and why resistance depends on temperature for metals and semiconductors.
3Circuit Symbols? Variable Resistor Ammeter Voltmeter Thermistor Cell Indicator or Light SourceDiodeLight Emitting DiodeResistorVariable ResistorThermistorLight Dependent ResistorHeaterElectric Motor
4Complete the Table V I R (a) 0.30 A 18 Ω (b) 12 V 88 Ω (c) 14.4 V
5AmmeterAn ammeter measures the current through part of the circuit. It is always connected in series.
6VoltmeterA voltmeter measures the potential difference between two points. It is always connected in parallel.
7CellA cell provides voltage to a circuit. This pushes the charge around the circuit.
8LampThe symbol for an indicator or any light source is the same (not including a light emitting diode).
9DiodeA diode only allows current to flow in one direction. (In the way the triangle points) The diode has a very high resistance in the reverse direction. (For LED add the two little arrows)
10ResistorA resistor impedes the flow of charge around a circuit. As it does so, it heats up.
11Variable ResistorA resistor that's value can easily be changed.
12ThermistorThe resistance of a thermistor decreases as the temperature increases.
13Light Dependent Resistor An LDR is a light dependent resistor. Its resistance decreases as the amount of light falling on it increases.
15Wire (Ohmic Conductor) For a resistor, the current-voltage graph is a straight line through the origin.The current through a resistor is directly proportional to the potential difference (voltage) across the resistor.
16Ohmic ConductorNote that for an Ohmic conductor the gradient of the line an I-V graph is equal to 1/R.But this is for an Ohmic conductor only.This is because R for a metallic conductor is constant under constant physical conditions.It does not apply for the filament bulb.
18Filament BulbFor a filament lamp, as the voltage increases, so does the current.But the increased current raises the temperature of the filament bulb which also increases the resistance.This is why the curve bends toward the end as itis increasingly difficult for more current to flow.
19Thermistor At constant T, it gives a straight line. The higher T is, the greater the gradient of the line as the resistance falls with increasing T.
21Diode NotesThe diode only allows current to flow in one direction (forward direction).The diode has a high resistance in the opposite direction (reverse direction).Needs a certain pd to conduct (typically about 0.6 V for silicon diode.)
22ApplicationsWhy does the resistance of metals increase with temperature?Positive temperature coefficient.Thermistor Temperature sensorsNegative temperature coefficient.% change of resistance.Why? number of charge carriers.