Questions tagged [ohms-law]

A well known relationship that describes the relationship between Voltage and current through a device's resistance expressed mathematically as V= IR. This formula says that voltage across the device is equal to the current through the device multiplied by the resistance.

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6answers
11k views

Why are resistor values constant in the face of changing voltage and current?

Small question, I see that resistors are labeled in certain increments (e.g 5, 10 50 Ohms), although a resistor outside of a circuit is completely without voltage and therefore current. Does this just ...
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1answer
933 views

Why can people touch high voltage?

So I know that you need a certain current flowing through you to die, I've heard from some people "its the amps that kills you", and from others "Its the volts that drive the amps" and I realize ...
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2answers
2k views

Does changing the Voltage and the Current passing through an LED affect the result in the same way?

More directly : passing electricity that is 0.5 times the amperage of the one required will make the LED half bright, right? Is it the same with halving its voltage requirement? Or will it not turn on ...
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8k views

Permanently dimming an incandescent light bulb

I have purchased a nice light bulb with long visible wires/resistors and plugged it in, on the ceiling. It burns too bright without a dimmer and does not look as intended (also the lifespan decreases)....
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5answers
943 views

Quick Question about ohms law and resistors

This may have been asked before, but I'm currently I'm an argument about whether or not passing 12v through a .1 ohm resistor would result in 120 amps due to Ohm's Law. (I=V/R) Providing that the ...
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3answers
3k views

Powering a device by USB?

I would like to power a device via the 5V USB port on a computer, because I will also be communicating with the computer via the USB data cables. I know that USB ports provide 5V, but from what I've ...
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5answers
5k views

Ohm's law of a circuit which has both a voltage source and current source

The voltage source has a specific voltage through it regardless of the circuit's current and its resistance while the current source has a specific current through it regardless of the voltage through ...
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3answers
544 views

Simple Ohm's Law Question

Do I need a resistor if \$\frac{V}{I}=0\$? I am working on a simple circuit of an LED and a buzzer in series where the voltage drop would be 2 and 3 volts, so \$R=\frac{V}{I}=\frac{(5 - (3 + 2))}{I}\...
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2answers
2k views

Convert 24 V to 20 mA (none is variable)

I have a PLC (take the "P" with a pinch of salt), it has some analogue inputs (4-20 mA) that I need to use to detect if 24 V is present or not. I can program the logic to say above X mA 24 V must be ...
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6answers
252 views

why does a step up transformer cause lower currents?

The usual answer I hear is because power needs to be conserved, but I dont find that answer satisfying. Normally if I were to double a supply voltage in a circuit, then I would expect twice the ...
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1answer
181 views

How much resistance will I need to drop the voltage?

9 Volts is applied to circuit. There is a LED which runs on 3 Volts. I want to drop 6 Volts. how much resistance (\$R_1\$) would I need for that?
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3answers
188 views

Same LED, different voltage drops with different supply voltages

I have an LED with no specs for it. I decided to measure the voltage drop across the LED, so I connected it to 5 V power supply and 325 ohm resistor. I measured the resistor with multi-meter, then I ...
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3answers
244 views

Why voltage is the same after placing a resistor?

simulate this circuit – Schematic created using CircuitLab Hi. I'm testing a very simple circuit with a multimeter. In Ohm's Law, a resistor should affect the voltage, but in my circuit it ...
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3answers
2k views

Does current source affect flow of current in circuit with a variable resistor?

Suppose you have a current source in series with a resistor R the current through the R resistor would be the current generated by the current source. How would the current through the circuit change ...
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1answer
219 views

How to prevent a resistor receiving a too high power?

If a circuit was creating 0.3 watts, and resistors rated for 1/4 watts were used, what would be the easiest way to make it stay inside the rating? Would it be to, say, connect two resistors of twice ...
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2answers
135 views

What is kU (V/V)

I have following task I know it's probably really simple (just simple Ohm's law), but I have no clue what kU is. Could anyone explain it to me in the simplest way possible.
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2answers
746 views

How do I work out what resistor to use?

I am trying to work out what resistor to use in a circuit. The circuit is a series circuit. The power to the circuit is 5.5V, with a switch, which connects to a GPIO pin on the RasberryPi. I believe ...
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3answers
143 views

Which current should I use to determine the Watt?

I am making a heated blanket and I have some troubles to determine the heat that will be generated. Resistance: Let say, I use this heated cable with a resistance of 0.3 Ohms/m*. If I am using 10m ...
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2answers
371 views

Calculate LED current when Vf is greater than source voltage

I'm planning on using an RGB LED in my project. \$V_f\$ is different for each die. My \$V_{cc}\$ is 3V. For the red diode, \$V_f=2V\$ and \$(I_f=20mA)\$, therefore I've calculated: $$R = \frac{3 - ...
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3answers
1k views

DC-DC Step-Down (buck) converter 5V 10A 50watt, not understand how to size the supply

I have a 5V 10A 50WATT DC step-down converter: http://www.powerstream.com/dc-24V-5V.htm I'm just not understanding how to size the power supply needed to drive this converter at max power. I have an ...
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2answers
917 views

Why does the voltage changes in this simple circuit?

I'm beginning to learn electronics, and there's something I just can't grasp. I was told that a high resistance in a circuit would lead to a smaller current passing through it, but the voltage would ...
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3answers
100 views

Further understanding Ohms Law

I posted a question earlier that helped me to understand Ohm's Law and how power is lost to length of wire due to resistance. So my original example was a 15A, 10ft cable surge protector plugged into ...
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2answers
92 views

How do voltages at outputs drop as current increases?

As I looked at some 74xxTxx ICs, such as this simple NAND gate, I noticed that the minimum \$V_{OH}\$ decrease as current flowing from the outputs increase. But, from my understanding of Ohm's law, \$...
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4answers
274 views

Is current calculation in copper wire for AC simple or not?

I'm trying to learn electronics by myself, and I'm starting with simple current calculations. Let's assume we have a straight wire of length L connecting a source and a sink. I know the voltage (V), ...
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2answers
74 views

Will the bright of the bulb increase or still the same in this simple circuit?

If Lamp2 is disconnected, What will happen to the brightness of the Lamp3? I think that the brightness will remain the same because Lamp2 is in parallel with the branch that contains Lamp3. Let's ...
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5answers
16k views

Why does a resistor reduce voltage if V=IR? [duplicate]

I'm sure this is a very simple question, but I have been confused about this topic for a while now. According to Ohm's law, resistance varies directly with voltage. This means that if resistance ...
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1answer
894 views

Choosing the correct thermistor

I need help choosing a thermistor. I’m not sure what I need to look for. Let’s say I have this circuit measuring temperature: I have a range of temperatures from 0 to 10 degrees that I need to ...
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3answers
2k views

Measuring the inductance of a coil?

I have a hand-wound coil I'm using in an LC Tank circuit. Using my multi-meter, I found out that the coil is drawing .6mA at 9v. Using Ohm's Law... $$R = V/I$$ $$R = 9/.0006$$ $$R = 15kΩ$$ Is there ...
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4answers
2k views

Ohm's law clarification

I am slightly confused about Ohm's law. I understand V = IR, and I did a simple experiment on paper. The results are slightly confusing, so I was hoping someone could tell me if I'm right? First, I ...
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2answers
48 views

Circuit Analysis Involving DC Motors

When it comes to simple circuit analysis, there is millions of tutorials on how to analyze a resistor circuit, a RC circuit, or those involving LED the non-ohmic devices. However, I did not find a ...
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1answer
76 views

Measured amperage differs greatly from my math

I've got the following circuit: simulate this circuit – Schematic created using CircuitLab It works. The LED glows nice and bright. However my math doesn't match the readings I'm getting from ...
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3answers
7k views

Max Voltage for Speaker of Given Power Rating

I have been looking into the design of loudspeaker drivers and would like to know how to determine the maximum voltage which can be delivered to a given speaker. From Ohm's law we know that P = V^2 / ...
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4answers
99 views

High voltage, low current and vice versa

Can someone please explain to me in simple terms how is it possible to have high voltage and low current and low voltage and high current and what actually does harm to human body. Here is what I don'...
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1answer
79 views

Power adapter giving a specified current [duplicate]

I often see power adapters indicating 5V 900mA (or) 5V 1000mA or sometimes 5V 3.4 A. Obviously they are converting current coming from 220V/110V source to 5V DC using some step down converter. But how ...
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2answers
100 views

Help understanding circuit with diodes in it

I'm having trouble figuring out how this circuit works in the real world. I know theoretically the diodes should have a resistance of 0, 0 and infinite respectively, which makes the question quite ...
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3answers
129 views

Solving for current through a wire

This is a pretty simple question really and I'll feel embarrassed when I get the solution but its bugging me for now. The goal is to solve for I going from left to right. No values given for any of ...
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3answers
491 views

Sparkfun using 500Ω resistor on circuit with 9V battery and 2V/0.018A LED

A Sparkfun tutorial explaining voltage, current and resistance shows a simple circuit where a LED is powered by a DC source (9V battery). The LED is a red 2V/0.018A LED. The tutorial explains that ...
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1answer
994 views

USB data serial termination resistors. Need them for STM32F2 micro? If so, what wattage?

I'm a little confused. The STM32F2 datasheet says only this, vaguely stated in the features: HNP/SNP/IP inside (no need for any external resistor) Is that referring to the D+/D- termination ...
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2answers
161 views

Ohm's Law vs. Conservation of Energy Misunderstanding

I am currently misunderstanding the relation between Ohm's Law and the law for conservation of energy. I am referring to the example (in the book "Foundations of Analog and Digital Electronic Circuits"...
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3answers
90 views

Struggling to understand series connections based on experiment

I'm having some issues understanding how series connections work based on an experiment I did at school. I took two lamps, and then connected them in series so the power initially goes to the first ...
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2answers
2k views

Measurement of power dissipation in a resistance

In the above figure (step up transformer), We can calculate \$V_s\$ using \$\frac{V_s}{V_p}=\frac{N_s}{N_p}\$ and \$V_s=50 V\$ So, power dissipated in the resistance, \$P=\frac{V_s^2}{R}=2500 W\$ (...
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1answer
834 views

Amp Limitation on 120v Circuit

If an engineer needs to limit how many amps come out of a wall's circuit, how is this accomplished? I know that there is nothing preventing more than 15 amps from coming through my wall other than the ...
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2answers
118 views

Maximum power/current for a battery?

I'm learning electronics and found this question below, which is exactly what I've been questioning myself. But there was no good answer there, so maybe someone here can help. Original question: ...
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1answer
29 views

Resistance/Voltage relation in Rheostat?

According to "How Computers Work" (Tenth Edition) by Ron White, he features a graphic of a potentiometer with three terminals on the bottom with the one on the left being for current flowing in and ...
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1answer
164 views

Fuel sender - need something to convert ohms to volts?

I need to connect a cars fuel sender(ohms) to a analog input on a GPS tracker (volts) Here's the catch, in our tests most fuel senders we worked with seem to send the data as ohms/resistance However,...
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1answer
134 views

Do I understand Ohm's law correctly?

I was reading a bachelor's thesis and it mentioned some technical details of a heated plate. Part of the technical details: MK2b Dual Power Technical Details [7] ...  Power Input: 12V or ...
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4answers
848 views

led resistor calculation, and resistor wattage?

I know this has been asked time and time again but bear with me as I am struggling to understand, so say I have this simple circuit here with 120v (dc for simplicity) as the input voltage and I have ...
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5answers
298 views

How are voltage dividers useful? I can't seem to get enough current for them to be useful

I must be doing something wrong here, because when I make my simple voltage dividers and do the math, the most current I could draw through my voltage divider would be 33.3mA. Here are my factors: ...
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2answers
49 views

Would lower current cause a battery to go flat slower?

So I understand the basics of ohm's law and batteries. The electrons move from the cathode to the anode via the circuit and when the anode and the cathode have the same amount of electrons they stop ...
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1answer
605 views

Mesh-Analysis, Ohm's Law & Passive Sign Convention

I am using Fundaments of Electric Circuits 5ed and I have a few questions about Passive Sign Convention with respect to Ohm's Law & PSC FYI passive sign current (PSC) is based on this diagram: ...