How to Find the Current through a 20 Ω Resistor: Magnitude and Direction

by Harry Harry
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Figure 1: what are the magnitude and direction of the current in the 20 ω resistor in (figure 1)?

The current through a 20 Ω resistor can be found by applying Ohm’s law. First, find what voltage is across it using equation (1) below. The answer will be greater than zero because there is some voltage across any resistor. Next, use equation (2) to find what resistance would produce this voltage; in this case, our unknown resistor has an impedance of 20 Ω. Finally, apply Ohm’s law to find what magnitude and direction of current flow through that resistance as shown by equations (3) and (4).

\[\begin{aligned} V &= IR\\ I &= \frac {V}{R}I_{MAX}. \\ 20 Ω&= ? A\\ 40.12 mA&=- 0.438 A\\ -0.538 A =- 20 ΩK_e^{+}\] In this circuit, the voltage across a resistor is greater than zero because the current has some resistance in it; for every unit of current passing through an impedance, there will be that much voltage between its two ends–as shown by equation (Eqn)

below: For one amp of current flowing into a 100 ohm load, what would be the total amount of volts between points “A” and “B”?

Some students confuse what voltage is all about by thinking that the circuit has two batteries, one on either end. The electrons can’t go through both of them at once! Voltage is just a measurement for how much potential energy there will be across a resistor. Volts are what we measure in order to find out what magnitude (size), or power, an electric current might have as it flows from point A to B with some resistance–as shown by equation (Eqn) below:

For example, if you have 100 volts between points A and B then the amperage would be 100/20 = 50 amps; this breaks down into 20 amp surges separated by periods when no electricity moves at all.

Introducing what is known as Ohm’s Law, which can be found in equation (Eqn) below:

Voltage equals current times resistance; or V = I x R. In this case for our 20 Ω resistor we have 100 volts and the amperage has to equal what? This means that if there are total of 50 amps then the voltage must also equal what? As you see on your calculator, 200 volts! Now it makes sense how much power is going through a circuit with more than one battery–it doesn’t matter what direction they’re facing because both batteries will provide some amount of energy between points A and B. Voltage isn’t like water where positive charges flow from point “A” to point “B” because there are no charges flowing in the direction of what is called a “positive” voltage.

A simple way to track what’s happening with current, voltage and resistance at each moment in time is by using what’s known as an ammeter or voltmeter. These meters measure what we call electrical quantity which can be measured on some type of scale (e.g., volts) but this will vary depending on what type of meter you’re using–the only one thing that matters for now is how they work! When the needle points downward it means that electricity moves from left to right; when the needle swings upward it indicates flow going in the opposite direction. So if you were reading your measurements sequentially,

what would this tell you about the current in a 20 kΩ resistor?

Figure (figure) shows what happens when we connect a DC power supply to wire leading into an LED. The negative terminal of the battery is connected to one end of the wires and then it goes through our series circuit (the resistor). If I were taking my voltage measurements with a voltmeter, what do they indicate about what is happening along that route: up or down? As shown in figure , if there are no changes due to where charges move on either side of both resistors–what does your ammeter show at any given moment?

In order for charge flow between points A and B below, what would the magnitude and direction of current in a 20 Ω resistor be? what are the magnitude and direction of the current in the 20 ω resistor in (figure ) ?

We have not yet addressed this question, but it is coming up soon. Stay tuned! :)

In order for charge flow between points A and B below, what would the magnitude and direction of current in a 20 Ω resistor be? The answer to this question will come up later on. For now just note that there is no way to know until we determine what resistors R_A or R_B represent. Once they’re known then we can calculate their resistance values using Ohm’s law: V = I

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