Lect_41 - Lecture 41 Real batteries. Kirchhoff's laws. DC...

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Lecture 41 Real batteries. Kirchhoff’s laws. DC instruments Galvanometer Galvanometer It is the most common current measuring device. Constant magnetic field Needle Pivoted coil Current through coil + Magnetic field Current I Restoring spring Torque (need 222!) Torsion of the spring Visible through the needle. Ammeter Used to measure current. Always in series with the circuit. Must have a very small resistance , so it does not affect the currents to be measured. A A G = r (shunt resistance or shunt) small
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Voltmeter Voltmeter Used to measure voltage or potential difference. Always in parallel with the circuit. Must have a very large resistance , so that very little current is diverted through it. V A B VG = R large Ohmmeter Ohmmeter Used to measure resistance. eq Galvanometer RrR =+ + G r (variable) R (to be determined) ε Ohmmeter G () Ir R + G I = ++ G = d d ?? d d Good measure Bad measure! 0 G rR = + d Good measure Must be adjusted for different ranges of 0 G ′ = ′ + r ’< ACT: Mixed circuit ACT: Mixed circuit Three identical bulbs are connected to an ideal battery as shown below. When the switch is closed, bulb 1 is __________ and bulb 2 is _________. A. dimmer, dimmer B. dimmer, the same C. brighter, dimmer 1 2 3 V 0
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1 2 3 Resistance here decreases I 1 Current 1 increases V 0 Bulb 1 is brighter Total resistance
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Lect_41 - Lecture 41 Real batteries. Kirchhoff's laws. DC...

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