Archive 2010
Tech Talk
By Jim Purvis WA7HRG
We were sitting around the restaurant one night drawing pictures on a napkin and reviewing ohms law. Made me stop and think bit. I thought it might be fun for the old timers to dig back in the memory banks and would be educational for those new hams that have heard about ohms law but never worked with it, to dust off the calculator, review the formulas, and sharpen up the #2 pencil.
The Law and where it came from
Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.
The mathematical equation that describes this relationship is:
The law was named after the German physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire. He presented a slightly more complex equation than the one above to explain his experimental results. The above equation is the modern form of Ohm's law. The V for voltage and the E for electromotive force have become interchangeable over time. You may see them both at times. For our purpose we will use E to represent voltage.
So to put in a little simpler terms;
Ohm's Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere.
( I ) Current is what flows on a wire or conductor like water flowing down a river. Current flows from negative to positive on the surface of a conductor. Current is measured in (A) amperes or amps.
( E ) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in (V) volts.
( R ) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in ohms.
( P ) Power is the amount of current times the voltage level at a given point measured in wattage or watts.
And here is your challenge.
The following diagram represents no specific circuit and holds no logical use that I can see. But it does present an interesting challenge. Your mission is to calculate all the voltage drops, currents, and power dissipated through each component. Also calculate the total current, total power dissipation and the total equivalent resistance. Calculate all values to at least four (.000x) decimals. (easy with a calculator). Answers will be presented in next months Gridleak.
Here is a review of a few formulas. They are all you will need to make all the calculations.
Resisters in series add together. R+R+R=
Resisters in parallel add algebraically. ___1_
1_ 1 1 =
R + R + R
I=E/R E=I*R R=E/I P=I*E P=I2*R P=E2/R
Find these Answers
Total equivalent resistance =
Total current Draw =
Total power dissipated =
Voltage drop across D1= R1= R2= R3= R4=
Current through D1= R1= R2= R3= R4=
Power dissipated by R1= R2= R3= R4=
Have fun and see you next month.
Jim
Tech Talk
By Jim Purvis WA7HRG
We were sitting around the restaurant one night drawing pictures on a napkin and reviewing ohms law. Made me stop and think bit. I thought it might be fun for the old timers to dig back in the memory banks and would be educational for those new hams that have heard about ohms law but never worked with it, to dust off the calculator, review the formulas, and sharpen up the #2 pencil.
The Law and where it came from
Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.
The mathematical equation that describes this relationship is:
The law was named after the German physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire. He presented a slightly more complex equation than the one above to explain his experimental results. The above equation is the modern form of Ohm's law. The V for voltage and the E for electromotive force have become interchangeable over time. You may see them both at times. For our purpose we will use E to represent voltage.
So to put in a little simpler terms;
Ohm's Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere.
( I ) Current is what flows on a wire or conductor like water flowing down a river. Current flows from negative to positive on the surface of a conductor. Current is measured in (A) amperes or amps.
( E ) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in (V) volts.
( R ) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in ohms.
( P ) Power is the amount of current times the voltage level at a given point measured in wattage or watts.
And here is your challenge.
The following diagram represents no specific circuit and holds no logical use that I can see. But it does present an interesting challenge. Your mission is to calculate all the voltage drops, currents, and power dissipated through each component. Also calculate the total current, total power dissipation and the total equivalent resistance. Calculate all values to at least four (.000x) decimals. (easy with a calculator). Answers will be presented in next months Gridleak.
Here is a review of a few formulas. They are all you will need to make all the calculations.
Resisters in series add together. R+R+R=
Resisters in parallel add algebraically. ___1_
1_ 1 1 =
R + R + R
I=E/R E=I*R R=E/I P=I*E P=I2*R P=E2/R
Find these Answers
Total equivalent resistance =
Total current Draw =
Total power dissipated =
Voltage drop across D1= R1= R2= R3= R4=
Current through D1= R1= R2= R3= R4=
Power dissipated by R1= R2= R3= R4=
Have fun and see you next month.
Jim