5.2+ELECTRIC+CIRCUITS

Back to IB PHYSICS > ELECTRIC CURRENTS 5.1 ELECTRIC POTENTIAL DIFFERENCE, CURRENT AND RESISTANCE
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5.2 ELECTRIC CIRCUITS
Define //electromotive force// (//emf//). EMF (E): The total electrical energy given by the battery to each coulomb of charge OR the terminal PD of the source when no current flows

Describe the concept of internal resistance. INTERNAL RESISTANCE: The resistance of the battery. Some of the energy provided by the source is converted to heat here and is not available in the external circuit components. TERMINAL PD: The PD measured across the terminals of the source which is less than the EMF due to the internal resistance of the source.

Apply the equations for resistors in series and in parallel

RESISTORS IN PARALLEL: Connected like a ladder. They all experience the same PD across them. RESISTORS IN SERIES: Connected like a chain. They all have the same current flowing through them.

This includes combinations of resistors and also complete circuits involving internal resistance Draw circuit diagrams. Students should be able to recognize and use the accepted circuit symbols.

Describe the use of ideal ammeters and ideal voltmeters. AMMETER: Instrument which measures current in a circuit. It must be connected in series with the current it measures and has a very low resistance. VOLTMETER: Instrument which measures PD in a circuit. It must be connected in parallel with the PD it measures and has a very high resistance. IDEAL METERS: These do not affect the readings they make. Ideal ammeters and voltmeters have zero and infinite resistances respectively.

Describe a potential divider POTENTIAL DIVIDER: The PD of a source is divided over two resistors in series in proportion to their resistances.

Explain the use of sensors in potential divider circuits. Sensors should include light-dependent resistors (LDRs), negative temperature coefficient (NTC) thermistors and strain gauges. ELECTRICAL SENSORS: A component whose electrical properties (usually resistance) changes with its physical conditions. THERMISTOR: A resistor whose resistance falls when its temperature rises. LIGHT DEPENDENT RESISTOR: A resistor whose resistance falls as the intensity of light falling on it increases. STRAIN GAUGE: A long thin wire whose resistance increases when it is stretched. POTENTIAL DIVIDER: The PD of a source is divided over two resistors in series in proportion to their resistances. SENSOR CIRCUITS: One of the resistors in a potential divider is replaced by a sensor so that the PD across the resistors in the potential divider changes as a physical condition changes (eg temperature, light intensity or strain).







9.0*8000/(87 700) = 0,82

Solve problems involving electric circuits. Students should appreciate that many circuit problems may be solved by regarding the circuit as a potential divider. Students should be aware that ammeters and voltmeters have their own resistance.