Direct Current CircuitsBasic componentsThe batterySlide 4Slide 5Slide 6The simplest circuit and the electric potential in a circuitAmmeter, Voltmeter and a DMMResistors in a circuitSlide 10Slide 11Slide 12More examplesSlide 14The Kirchhoff’s RulesSlide 16One more exampleSlide 181Direct Current CircuitsDirect Current (DC) and circuits:Direct Current: the DIRECTION of the current in a circuit does not change with time. The amplitude of the current may or may not change with time.The opposite, the Alternating Current (AC): the DIRECTION of the current in a circuit changes with time. The amplitude of the current usually changes with time as well, but may also stay constant. Battery operated circuits have usually DC.2Basic componentsBasic components and their symbols:Wire: connects other components in the circuit, without any resistance. Symbol: Switch: when it is closed, a circuit (a loop for the current) is formed. Symbol: Resistor: the component that follows the Ohm’s Law .Symbol: Capacitor: the component that is defined through . Symbol:Battery: the device that provides the electric potential difference in a circuit, that converts other type of energy into electric. Symbol:Inductor: will be discussed later part of this semester.Transistor: not in the scope of this course.… …IVR VQC or+3The batteryThe electromotive force (emf, E) of a battery:The capacitance of a battery:This is often specified as Amphour or a variation of this unit (like mAh)The internal resistance and the terminal voltage:The external force (mechanical or chemical) that provides the potential difference is called the electromotive force. For a battery, this emf comes from chemical reactions.4The batteryThe internal resistance and the terminal voltage:The battery’s emf is 1.50V and its internal resistance is 0.0336 ohm. What is the terminal voltage with a 5 ohm resistor load?Question: how do you measure the emf?5The batteryMaximum efficiency of the battery and the maximum power the battery can deliver. The efficiency is defined as:R, the loademf, EWith a load R, the power delivered to the load is:6The battery7The simplest circuit and the electric potential in a circuitThe simplest circuit:The electric potential in the loop:8Ammeter, Voltmeter and a DMMAmmeter:Voltmeter:DMM: digital multi-meter (ammeter, voltmeter, ohmmeter, ……) Ammeters measure current. Always connect the ammeter in the circuit and the current flows through the ammeter. The internal resistance of an ammeter is very small. Voltmeters measure voltage. Always connect the voltmeter across the component of which the voltage over it is to be measured. The internal resistance of an voltmeter is very large.9Resistors in a circuitOne resistor in a circuit Ohm’s Law. Two resistors connected inSeriesParallel10Resistors in a circuitCurrent, voltage and power division over two resistors when they are inSeriesParallel11Resistors in a circuitThree resistors connected inSeriesParallel12Resistors in a circuitMixed connections13More examplesWhat is the total current I, and the current, voltage and power over each resistor?14More examples15The Kirchhoff’s RulesThe Kirchhoff’s rulesThe loop rule:The sum of the changes in electric potential across all components around any complete loop of a circuit is zero. The junction rule:The total current flowing into a junction equals the total current flowing out of a junction. Steps in solving a problem:16More examples17One more exampleWhat current flows through the 5.00 Ω resistor?18One more
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