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Current, resistance, and electromotive constrain (emf): Chapter 25 (sec. 1-5) Charges (electrons) moving in a conduit Ohm's Law & imperviousness to stream of charge Energy and power in electrical circuits C 2012 J. Becker

Learning Goals - we will learn: • The significance of electric current , and how electric charges move in a conveyor. • What is implied by the resistivity of a substance. • How to compute the resistance of a conductor from its measurements and its resistivity. • How an electromotive constrain ( emf ) makes it possible for current to stream in a circuit. • How to do computations including vitality and control in circuits.

ELECTRON MOTION IN A CONDUCTOR WITH AND WITHOUT AN ELECTRIC FIELD

ANALOGY OF A CHARGE MOVING IN A CONDUCTOR 12 Volts 0 Volts

CONDUCTOR WITH CONVENTIONAL CURRENT MOVING FROM HIGH ELECTRICAL POTENTIAL (VOLTS) TO LOW POTENTIAL

"Customary" CHARGES DRIFTING IN A CONDUCTOR HIGHER POTENTIAL LOWER POTENTIAL LAMP

Which Box (A, B, or C) has the most imperviousness to the stream of electric charge (current)? Every light has a similar measure of imperviousness to the stream of charge. Current is the stream of charge past a point in the circuit per unit time interim. C 1998 McDermott, et al., Prentice Hall

Which arrange has the most imperviousness to the stream of charge? Rank the systems as indicated by diminishing resistance. C 1998 McDermott, et al., Prentice Hall

Rank the splendor of the knobs (brilliant to diminish). 2. A wire is included as demonstrated as follows. Does the brilliance of knob C increment, diminish, or continue as before? Does the shine of globule An expansion, diminish, or continue as before? Does the current through the battery increment, diminish, or continue as before? C 1998 McDermott, et al., Prentice Hall

Resistance (R) is relative to resistivity ( r ) : R = r L/A The resistivity ( r ) relies on upon temperature and the physical properties of the material, so it has an alternate an incentive for every material. Temperature reliance of resistance (and resistivity) is for the most part straight over constrained temperature goes and is portrayed by the temperature coefficient of resistivity ( a ): R(T) = R 0 [ 1 + a (T-T 0 )] r (T) = r 0 [ 1 + a (T-T 0 )] where R 0 and T 0 are the resistance and temperature at a standard temperature, for the most part room temperature or 20 o C. (Measured in Lab #5)

Current – voltage relations a resistor complies with Ohm's Law: I = V/R with consistent slant = 1/R (or D V = I R ) b) A vacuum tube diode c) A semiconductor diode

Electric potential ( D V) rises and drops in a circuit (from past slide)

CIRCUIT ENERGY and POWER P = V stomach muscle I = I 2 R = V abdominal muscle 2/R e I = rate of transformation of non-electrical (synthetic) vitality to electrical vitality inside the source I 2 r = rate of electrical vitality scattering in the inward resistance of the source (battery) e I - I 2 r = the rate at which the source conveys electrical vitality to the heap (fog light) R

You can see a 4-minute youtube video of a smoke finder and how it functions, from schoolmate Marjo Mallari http://www.youtube.com/watch?v=oFUUQcpGR3k

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