ECE201Lect-2-1

ECE201Lect-2-1 - Ohm's Law(2.1 Kirchhoff's Laws(2.2 Dr...

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ECE201 Lect-2 1 Ohm's Law (2.1); Kirchhoff's Laws (2.2) Dr. Holbert
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ECE201 Lect-2 2 Resistors A resistor is a circuit element that dissipates electrical energy (usually as heat) Real-world devices that are modeled by resistors: incandescent light bulbs, heating elements (stoves, heaters, etc.), long wires Resistance is measured in Ohms ( )
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ECE201 Lect-2 3 Ohm’s Law v ( t ) = i ( t ) R - or - V = I R p ( t ) = i 2 ( t ) R = v 2 ( t )/ R [+ (absorbing)] The Rest of the Circuit R v ( t ) i ( t ) +
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ECE201 Lect-2 4 Example: a 25W Bulb If the voltage across a 25W bulb is 120V, what is its resistance? R = V 2 / P = (120V) 2 /25W = 576 What is the current flowing through the 25W bulb? I = V / R = 120V/576 = 0.208 A
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ECE201 Lect-2 5 Thought Question When I measured the resistance of a 25W bulb, I got a value of about 40 . What’s wrong here? Answer : The resistance of a wire increases as the temperature increases. For tungsten, the temperature coefficient of resistivity is 4.5x10 -3 / o K. A light bulb operates at about 5000 o F.
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ECE201 Lect-2 6 Open Circuit What if R = ?
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ECE201Lect-2-1 - Ohm's Law(2.1 Kirchhoff's Laws(2.2 Dr...

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