# 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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### How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

simulate this circuit – Schematic created using CircuitLab My physics teacher said that the current through the resistor is 4A because each battery has a current of 2A if hooked up to the ...
8k views

### Why don't we use low voltage Power Sources for high wattage applications?

Super nooby question involving Ohm's law, but this has been on mind this morning. Say I have a 60W device, and I want to power it. Usually this calls for a 120V source or something. However, why not ...
30k views

### Where does U for voltage come from?

I believe in Europe the letter U is commonly used for voltage in (eg.) Ohm's law $U = I × R$. I think I understand where the letter V came from, commonly used in North America. But what's the story ...
63k views

### Why do we need resistors in led

I've researched and it says that resistors limit the current flowing through the LED. But this statement confuses me because we know that in a series circuit, the current is constant at every point, ...
60k views

### accounting for LED resistance

I'm doing a simple lab (I'm a hobby EE) to reinforce my ohm's law math and learn a little about how to do proper measurements with a multimeter. I have simple circuit with a 2.2k ohm resistor ...
15k views

### Does a diode really follow Ohm's Law?

Does a diode really follow Ohm's Law? Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant ...
89k views

### How can a resistor affect current AND potential at the same time?

Though the resistor is always introduced as one of the most simple components it is the one which makes least sense to me. Ohm's law defines the resistance as$$R = \frac{V}{I}$$ this means that the ...
4k views

### How did scientists deal with electronics' problems before Kirchhoff and Ohm's laws?

Both physicists developed really powerful laws which still nowadays rule the electronic behavior of circuits. These help us every day to solve problems, calculate circuit variables… but how did ...
6k views

### Ohm's law doesn't seem to be working for this electric motor

I'm a beginner in this field so please forgive me if I'm confusing with my question. There is a component that I can't understand with Ohm's law which is a washing machine drain pump. Washing machine ...
7k views

### What are the consequences of oversizing resistors?

When building a circuit to power an LED, we use Ohms law to calculate the required resistance, then to calculate the required wattage of the resistor. Suppose this formula dictates a 1/8 W resistor, ...
19k views

### Why do diodes have a voltage drop?

Is resistance what makes a diode have a voltage drop? Or is it impedence? If it is electrical energy being converted to light, please tell me what this effect is called.
7k views

### Why are these readings violating ohm's law? (Are they?)

I'm brushing up on my high school electronics knowledge and I decided to experiment with a small acquarium pump I had lying around. I took some measurements with a multimeter and the results confuse ...
41k views

### Why does an LED have a maximum voltage?

When powering a simple LED circuit (DC power source, LED, resistor), does the supply voltage matter, as long as the correctly calculated current limiting resistor value is used? In other words, is ...
4k views

### Powering a 5v relay from a 12v power supply

I have a relay which is rated for 5v. My power supply is 12v. I have measured the resistance across the coil as 400 ohm. If I place the relay in series with a resistor that is 560 ohm, would it ...
40k views

### How do I calculate the necessary resistance for a voltage divider?

I’m self-taught, and this is a little bit of a thought experiment for me to understand Ohm’s Law better. I have a very simple voltage divider. Given a 15V DC input, each of three 4.7KΩ resistors ...
20k views

### Why do LEDs not obey Ohm's law?

In a previous question, it was brought to me that LEDs do not obey the Ohm's law. (See Calculate expected voltage around a resistor) Simply put: how is that? What makes them behave so differently? ...
12k views

### How to choose correct resistor with proper wattage and ohms for 6 leds connected in a serial circuit?

Let's suppose I've six LED lights with each 3.2 Volt and 20mA and all six of them are connected in one serial circuit. I know there is better setup but for this I'm using this circuit setup. I'm ...
699 views

### I do not understand what power actually is

I realize this is probably a super common question, but I have to put it in my own words. I try to understand ohm's law with the water analogy. Two tanks with water, one with a higher level than the ...
4k views

### How a DC motor works when connected to a power supply but no resistor?

I connected a 12V DC motor to a battery of 12V only. The motor rotated perfectly fine. But my question is that if you don't have a resistor attached to the circuit, as per theory the current is ...
17k views

### Does a generator produce voltage or current?

I know that this question might sound very stupid for +90% of you, but my brain doesn't really get the electricity generation. The thing that I don't understand is what does a generator produce, ...
2k views

### Why is my circuit's current far lower than expected with 2.6v / 220Ohm / and LED?

I have a very simple circuit which I have measured the current to be only 3mA but should be in the range of 18mA. I have a simple circuit using 2 AA batteries (NiMH) at 1.3V each in series for a total ...
9k views

### How can 4 resistors of 30ohms each be connected so you end up with a resistance of 18ohms?

An association of 4 resistors of 30ohms each, how can one assemble them so you get a resistance equivalent of 18ohms?
2k views

### Amps / current doesnt add up to the expected figure - Ohm's law failure on my part!

Can anyone offer suggestions as to where I am going wrong please? In my circuit (diagram below) the system voltage is 12.03 V and the lamp resistance is 2.9 ohms (measured with power disconnected ...
2k views

### How do resistors limit current for an LED? [closed]

If I have an LED with Vf = 2.1V and I = 20mA, Ohm's Law says I should have a resistor in series at a value of R = 145Ω, if the voltage supply is Vs = 5V. However, I believe can put a higher valued ...
53k views

### Power's relationship to Resistance

$$\frac{V^2}{R} = P = I^2 \cdot R$$ According to this equation, Power is inversely proportional to resistance on the left side and directly proportional to resistance on the right side. How can ...
604 views

### How can current-limiting supplies be possible?

Knowing Ohm's law, the current drawn is directly proportional to the resistance. In some power supplies, you can limit the current. Let's say the voltage is 12 volts, it supplies 1 amp, and the ...
1k views

### How to understand this circuit?

I'm studying about Ohm's Law, and the following problem perplexed me. The answer is $I_{t} = 11$mA and $U_{r} = 41$V. What I need to find is $U_{t}$ and $I_{t}$. The only thing I've found so ...
39k views

### How is current lowered as Voltage is increased in AC power transmission

I was reading about power transmission on wikipedia and came across the explanation of the efficiency of AC power transmission that said power in the load = (I^2)* R while power transmitted= IV. The ...
11k views

### Joule–Lenz Law.. Forgotten history? [closed]

We are all, or should be, extremely familiar with this graphic. It is course the magic triangle used to represent Ohm's Law. We should all also be very familiar with the similar power triangle. ...
5k views

### Why does voltage drop across resistance contradict Ohm's law?

Very basic question here. I have been learning a ton about Ohm's law, and I don’t seem to ever be able to completely understand it. One of which I am getting particularly confused about is voltage ...
3k views

### Batteries have zero voltage

According to Ohm's law V=IR. This means that if the current is zero there is no voltage. Does this mean also that an unplugged battery has zero voltage? Then why does it say otherwise in the package. ...
1k views

### How current works

I apologize for the very basic question but I seem to be lacking some fundamental knowledge. I am using an infra red LED in a circuit and it seems like it is drawing around 15mA at 5v. I was told ...
2k views

### Why does current only choose path of least resistance sometimes

Say we have the following setup simulate this circuit – Schematic created using CircuitLab Input is pulled high and current flows through it as long as the switch is open. As soon as it closes ...
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### How do ohm meters measure high resistances?

I'm sorry if this is a stupid question, but I'm an apprentice and this doesn't make sense to me. I'm given to understand that an ohm meter measures resistance by passing a small current through a ...
13k views

### Why does current change when adding in an LED?

In the following diagram: The current is 1 mA from: V = IR R = 1 / 1000 = 1 mA However, when I add in an LED with forward voltage 1V: Why does adding in the ...
820 views

### How does a 'voltage drop' work?

It is my understanding that, in an electric circuit, voltage is divided amongst components in a ratio determined by their various resistances. That is, for example, if a 5Ω‎ and a10Ω‎ resistor were ...
2k views

### With parallel termination of a transmission line, why does the receiver see the full voltage?

With parallel termination of a transmission line, the line characteristic impedance $Z0$ is matched with the pull-down resistance $Rt$. But, in that case, shouldn't the receiver see half of the ...
895 views

### When does a resistor affect current and voltage?

I was playing around with a computer power supply and some resistors and noticed that raising the ohmage decreased the amperage but the voltage was unaffected. Does this mean that voltage is a ...
279 views

### Understanding “Current Draw” in terms of “Ohm's Law”

I'm having trouble understanding Current Draw as it relates to Ohm's Law (V = IR). I have a power supply rated at 5V and 500mA. I'm trying to power a string of LED lights. According to my ...
221 views

### Voltage distribution between components

I often see the same method for computing voltage distribution in electronic circuits implying components whose V-I curves are not trivial. For example, in a circuit implying a resistor and a LED ...
2k views

### What's the correct term to describe a conductor which doesn't always obey Ohm's law?

Non-ohmic comes to mind, but that gives an impression that the conductor never satisfies Ohm's law. Is there a better term which describes a conductor which might satisfy Ohm's law at certain voltages ...
3k views

### Understanding voltage drop

Meanwhile in quarantine I been trying to learn about electronics. I am still not able to understand the voltage drop when it comes to long wires. My goal is to be able to send a 5v signal over a very ...
4k views

### Why does an infinitely decreasing resistance infinitely increase current?

So I have been mulling over Ohm's law for hours today. It makes sense to me that the current gets bigger as voltage rises, since the voltage is supplying more electrons and current is the number of ...
18k views

### Ohm's Law confusion — can there be voltage without current?

I know there has been asked a similar question about this before but I still have some issues to understand the whole voltage and current thing. ( Current without Voltage and Voltage without Current? ...
2k views

### High voltage transmission, transformers and Ohm's law

I have difficulties with understanding high voltage transmission and transformers working process. Particularly with this expression: "the higher the transmission line voltage, the smaller the current"...
2k views

My first question on EE, please be kind. :-) I am trying to learn how the ADC works on this Cypress PSoC 4100 board. The circuit in the picture does nothing but power the board, connect it to the ...
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### LED current limiting resistor and Ohm's Law

Yesterday I was trying to figure out how many ohms of resistor should I be using for my LED, and found this post right here in the forum. The formula states that one should subtract the voltage drop ...
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### Sharing a pull-up resistor

I have two IC chips. On one chip I have one 10K ohm pull-up resistor and on another chip I have three 10K ohm pull-up resistors. At first I was using four through hole pull-up resistors. Then I ...