ECEN 301Discussion #4 – Ohm’s Law1 DateDayClass No. TitleChaptersHW Due date Lab Due date Exam 15 SeptMon4Ohm’s Law2.5 – 2.6 LAB 1 16 SeptTue 17 SeptWed5Ohm’s Law SeptThu LAB 1 29 SeptFri Recitation HW 2 20 SeptSat 21 SeptSun 22 SeptMon6Practical Sources2.6 – 2.8 LAB 2 23 SeptTue Schedule…

ECEN 301Discussion #4 – Ohm’s Law2 High Resistance to Evil, Low Resistance to Good James 4:7 7 Submit yourselves therefore to God. Resist the devil, and he will flee from you. Alma 61:14 14 Therefore, my beloved brother, Moroni, let us resist evil, and whatsoever evil we cannot resist with our words, yea, such as rebellions and dissensions, let us resist them with our swords, that we may retain our freedom, that we may rejoice in the great privilege of our church, and in the cause of our Redeemer and our God.

ECEN 301Discussion #4 – Ohm’s Law3 Lecture 4 – Resistance & Ohm’s Law

ECEN 301Discussion #4 – Ohm’s Law4 Resistance uResistance (R): opposition to the flow of current ÙMagnitude depends on electrical properties of the material ÙAll circuit elements exhibit some resistance ÙMay be undesirable ÙCauses electric energy to be transformed into heat ÙElement symbols: Ohm (Ω): electric resistance unit. 1 Ohm = 1 Volt/Ampere (V/A)

ECEN 301Discussion #4 – Ohm’s Law5 Conductance uConductance (G): the inverse of resistance siemens (S): electric conductance unit. 1 siemens = 1 Ampere/Volt (A/V)

ECEN 301Discussion #4 – Ohm’s Law6 Resistance uResistivity (ρ): a materials property which determines resistance uConductivity (σ): the inverse of resistivity (determines conductance) l A +v_+v_ R i

ECEN 301Discussion #4 – Ohm’s Law7 Resistance uCommon resistors are made of cylindrical sections of carbon (resistivity ρ = 3.5x10 -5 Ω-m) b4b4 b3b3 b2b2 b1b1 black0Blue6 brown1 (1%)violet7 red2 (2%)gray8 orange3white9 yellow4silver-2 (10%) green5gold-1 (5%) None(20%)

ECEN 301Discussion #4 – Ohm’s Law8 Resistance CodeΩMultΩ k ΩMultk ΩMultk ΩMult Brn-blk10Black100Brown1.0Red10Orange100Yellow Brn-red12Black120Brown1.2Red12Orange120Yellow Brn-grn15Black150Brown1.5Red15Orange150Yellow Brn-gry18Black180Brown1.8Red18Orange180Yellow Red-red22Black220Brown2.2Red22Orange220Yellow Red-vlt27Black270Brown2.7Red27Orange270Yellow Org-org33Black330Brown3.3Red33Orange330Yellow Org-wht39Black390Brown3.9Red39Orange390Yellow Ylw-vlt47Black470Brown4.7Red4.7Orange470Yellow Grn-blu56Black560Brown5.6Red5.6Orange560Yellow Blu-gry68Black680Brown6.8Red6.8Orange680Yellow Gry-red82Black820Brown8.2Red8.2Orange820Yellow

ECEN 301Discussion #4 – Ohm’s Law9 Resistance uExample1: what is the value of the resistor? b4b4 b3b3 b2b2 b1b1 black0Blue6 brown1 (1%)violet7 red2 (2%)gray8 orange3white9 yellow4silver-2 (10%) green5gold-1 (5%) None(20%)

ECEN 301Discussion #4 – Ohm’s Law10 Resistance uExample1: what is the value of the resistor? b4b4 b3b3 b2b2 b1b1 black0Blue6 brown1 (1%)violet7 red2 (2%)gray8 orange3white9 yellow4silver-2 (10%) green5gold-1 (5%) None(20%)

ECEN 301Discussion #4 – Ohm’s Law11 Resistance uExample2: what resistor has a value of 6.2M Ω? b4b4 b3b3 b2b2 b1b1 black0Blue6 brown1 (1%)violet7 red2 (2%)gray8 orange3white9 yellow4silver-2 (10%) green5gold-1 (5%) None(20%)

ECEN 301Discussion #4 – Ohm’s Law12 Resistance uExample2: what resistor has a value of 6.2M Ω? b4b4 b3b3 b2b2 b1b1 Blue Red Green black0Blue6 brown1 (1%)violet7 red2 (2%)gray8 orange3white9 yellow4silver-2 (10%) green5gold-1 (5%) None(20%)

ECEN 301Discussion #4 – Ohm’s Law13 Ohm’s Law uThe voltage across an element is directly proportional to the current flow through it OR +v_+v_ R i 1/R

ECEN 301Discussion #4 – Ohm’s Law14 Ohm’s Law uOhm’s law is only a simplification ÙOhm’s law is not applicable: At high voltages or currents At high frequencies Over long distances For some materials For our class Ohm’s law will apply!

ECEN 301Discussion #4 – Ohm’s Law15 Ohm’s Law uOhm’s Law only applies to a portion of an electrical element’s the i–v graph

ECEN 301Discussion #4 – Ohm’s Law16 Ohm’s Law uExample3: What is the resistance of the element with the following i–v characteristic?

ECEN 301Discussion #4 – Ohm’s Law17 Ohm’s Law uExample3: What is the resistance of the element with the following i–v characteristic? 1/R

ECEN 301Discussion #4 – Ohm’s Law18 Power Rating upower rating: maximum allowable power dissipation ÙCommon power rating is ¼ W uExceeding the power rating for an electrical element will cause the element to burn up! ÙAlways consider power ratings!!

ECEN 301Discussion #4 – Ohm’s Law19 Power Rating uExample4: With a ¼ W rating, what is the minimum resistor size (R) that can be used in the following: VsVs + _ i +R1–+R1– 1.5V V s1 + _ i +R2–+R2– 1.5V V s2 – + 1.5V

ECEN 301Discussion #4 – Ohm’s Law20 Power Rating uExample4: With a ¼ W rating, what is the minimum resistor size (R) that can be used in the following: VsVs + _ i +R1–+R1– 1.5V V s1 + _ i +R2–+R2– 1.5V V s2 – + 1.5V

ECEN 301Discussion #4 – Ohm’s Law21 Power Rating uExample4: With a ¼ W rating, what is the minimum resistor size (R) that can be used in the following: VsVs + _ i +R1–+R1– 1.5V V s1 + _ i +R2–+R2– 1.5V V s2 – + 1.5V NB: Doubling the amount of voltage has a quadratic effect on minimum resistor size

ECEN 301Discussion #4 – Ohm’s Law22 Power Rating uExample5: find the power supplied by the battery ÙV s = 3V, i 1 = 0.2mA, i 2 = 0.4mA, i 3 = 1.2mA isis i1i1 i2i2 i3i3 +R1–+R1– VsVs + _ +R2–+R2– +R3–+R3–

ECEN 301Discussion #4 – Ohm’s Law23 Power Rating uExample5: find the power supplied by the battery ÙV s = 3V, i 1 = 0.2mA, i 2 = 0.4mA, i 3 = 1.2mA isis i1i1 i2i2 i3i3 +R1–+R1– VsVs + _ +R2–+R2– +R3–+R3– Node a

ECEN 301Discussion #4 – Ohm’s Law24 Power Rating isis i1i1 i2i2 i3i3 +R1–+R1– VsVs + _ +R2–+R2– +R3–+R3– uExample6: find the voltages and resistances of R 1, R 2, R 3 ÙV s = 3V, i 1 = 0.2mA, i 2 = 0.4mA, i 3 = 1.2mA

ECEN 301Discussion #4 – Ohm’s Law25 Power Rating uExample6: find the voltages and resistances of R 1, R 2, R 3 ÙV s = 3V, i 1 = 0.2mA, i 2 = 0.4mA, i 3 = 1.2mA isis i1i1 i2i2 i3i3 +R1–+R1– VsVs + _ +R2–+R2– +R3–+R3–

ECEN 301Discussion #4 – Ohm’s Law26 Power Rating isis i1i1 i2i2 i3i3 +R1–+R1– VsVs + _ +R2–+R2– +R3–+R3– uExample6: find the voltages and resistances of R 1, R 2, R 3 ÙV s = 3V, i 1 = 0.2mA, i 2 = 0.4mA, i 3 = 1.2mA