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Unformatted text preview: meter’s internal resistance 303L: DC Circuits (Ch.28) 303L: DC Circuits (Ch.28) Electrical Meters Household Wiring Voltmeter Distribution of electrical power A device that measures potential difference Each home connected in parallel to a pair of wires • The potential difference between two
points in a circuit • Neutral wire parallel grounded, i.e., has zero potential connection • Live wire has potential difference 120 V with the neutral wire
• Ideally, a voltmeter should have infinite resistance so that no current • Meter exits in it • Circuit breaker • Large series resistor in series with the live wire
controls individual circuit reduces I through a galvanometer and increases
the voltmeter’s internal resistance • Heavy-duty appliances
• Third wire operate on 240 V has potential difference -120 V with the neutral wire 303L: DC Circuits (Ch.28) 303L: DC Circuits (Ch.28) 2 Electrical Safety SUMMARY Short circuit Direct Current Circuits
• The emf of a battery is equal to the voltage across its terminals when the • Short circuit occurs when almost zero resistance exists
between two points at different
potentials very large I current is zero
• Equivalent resistance of a series combination of resistors: Req = R1 + R2 + R3 + ...
= + + + ...
• Equivalent resistance of a parallel combination of resistors:
Req R1 R2 R3
• Kirchhoff’s rules: • All new electrical installations
require 120-V outlets to accept
a three-pronged power cord • junction rule • loop rule ∑I =∑I
∑ ∆V = 0
in out closed loop • RC circuit:
• Round prong ground wire – casing of appliance 303L: DC Circuits (Ch.28) • time constant • charging capacitor • grounded and connected to the τ=RC discharging capacitor ( q (t ) = Cε 1 − e − t τ ) q (t ) = Cε e − t τ 303L: DC Circuits (Ch.28) 3...
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