# Tagged Questions

It's a measure of how much an conductor opposes current flowing through it. It can also refer to a part of a circuit, which has a non-negligible resistance value.

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### Measure resistance and capacitance with bias in low frequencies

I have a device which can be modeled with a resistor in parallel with a capacitor. Now I want to measure its resistance and capacitance as a function of voltage bias (from -2V to 2V) and frequency ...
4answers
125 views

### Why is the series resistor getting hot in this LED driving circuit?

I am trying to create the circuit below but then the resistor is getting too hot. I think is has something to do with my power source 15V, 8A. My resistor is 51 ohms, 1/4W. Any comment please... ...
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### Determining resistance per load with only power and volts

I have a extra credit problem in my class and I'm slightly stumped as to where to go next after I determine the It, Et and Rt. I am starting with a total power of 2 watts and 32 volts. I know to get ...
2answers
163 views

### Why does a multimeter put more voltage to measure a smaller resistance?

I noticed this behaviour on two different multimeters (different models and brands as well). At first I did not put a multimeter in the way to measure how much voltage changed for the different scales ...
0answers
71 views

### Is it possible to count human with low current?

Please look at this project http://big.dk/#projects-vvv Description says "A single person can activate the beating heart, but joining hands with others will make the heart beat even faster to create ...
3answers
164 views

### How to measure a resistance very accurately?

How can I measure a resistance very accurately more than a multimeter (ohmmeter)? For our measurement we are using resistances with values such as 300.8974083. But the instrumentation is very old ...
2answers
4k views

### Connecting LEDs to a 9V battery

1) I have 6 4.5V 20mA LEDs and have connected them to a common 9V battery. Doing this I made 3 parallel circuits with 2 LEDs in each. Now, I see that most pages that describe LED circuitry say that ...
2answers
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### Series - Parallel Resistor Calculations

Hi, I would be very grateful if anyone could shed some light on the below diagram as I'm trying to calculate the total resistance between A and B in this series parallel configuration. 10 and 20 ...
1answer
52 views

### Measuring input resistance to a MOSFET/BJT amplifier

How would one go about measuring the resistance of a Emitter follower in PSPICE?
2answers
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### Telegrapher's equations

Something about the derivation of Telegrapher's equation is really bugging me. When deriving the Telgrapher's equations for a transmission line using a model as shown above, why do we only use a ...
2answers
183 views

### What is negative Resistance

I have heard some people talk a bit about negative resistance, but I have never really understood it. What is negative resistance?
3answers
120 views

### Simple measurment of resistance with microcontroller

What is a simple way to measure resistance (in this case 0-100 kOhm) using micro-controller (I'm using STM32, it has 12-bit ADC, timer, but no comparator). I want it simple (not too many components) ...
3answers
115 views

### What is Kirchhoff's voltage law all about?

what is the Kirchhoff voltage law ? isnt it the sum of potential drops as we move along a circuit till the same point should be zero it is simply energy conservation law that when the battery ...
1answer
179 views

### What mechanism happens inside a resistor for potential drop and constant current?

What process happens inside the resistor just after being connected to a battery? I am trying to get a picture of it. On applying a potential difference, the electric field it generates pushes the ...
4answers
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### Resistors and the water analogy

The the most prevalent analogy for understanding electricity is the water hose one. I personally like this because it's very understandable but I have a question about how this works with resistors. ...
2answers
153 views

### How do I identify identify if a resistor is 300 or 1k? [duplicate]

I got an Arduino-compatible board from this indiegogo campaign and the kits come with 10 330-resistors and 10 1k-resistors, but I don't know how do I identify which resistor is which. The board forums ...
2answers
129 views

### Behavior of capacitor with infinite capacitance at steady state (DC analysis & AC Analysis)

What is the behavior of the capacitor below at steady state (DC/AC Analysis)? simulate this circuit – Schematic created using CircuitLab
1answer
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### Is there not enough power for relay?

I can't get the relay to work in my example. Transistor gets really hot. When connecting&disconnection relay wire between diode and transistor and I can hear soft click from relay. But when ...
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### Equivalent resistance with complicated net

I'm completely lost as to how to find the equivalent resistance of this circuit: It's R6 that's causing me problems. I can't find an expression since a bunch of nodes connect to each other. Anyone ...
1answer
415 views

### Does adding thermal relief on PCB increase electrical resistance?

I am just getting started on PCB design (for fun) and came across this term called thermal relief. It increases thermal resistance so the components can be soldered easily. But according to what I ...
2answers
154 views

### Decade resistance box with BCD-type rotary switches

I'm looking at building my own decade resistance box, but the typical rotary switches are... quite expensive. They seem to be the most expensive part of the entire project. Whether I choose a real ...
2answers
65 views

### Reading Voltage NTC Sensor, Unexpected Behaviour

Below pictured is the basic circuit im working with, NCT is apparently pretty much a variable pot resistor. The measuring point ive added. According to the manual for my car, the sensor is provided ...
0answers
152 views

### Why does a multimeter in resistance mode show initial continuity over a diode?

I originally phrased this question very differently; the original text is retained below in case background information is useful to clarify the context. When I using this digital multimeter to ...
2answers
75 views

### Potentiometer voltage change

I'm trying to understand simple things about electricity reading allaboutcircuits.com web. This chapter includes image which´s principle I don't understand. Here it is: When supplying constant ...
2answers
72 views

### Simple circuit with resistors

Knowing that I1 = 100mA, I3 = 300mA, UR2 = 10V, determine R2. So I tried it like this: we know that in parallel connection, the voltage stays the same so UR2 = UR1 = 10V. Then, R1 = U1 / I1 = ...
4answers
99 views

### Replacing resistors with equivalent resistor

This is somewhat a homework assignment, but please bear with me. Given the following schematic, I want to know the overall resistance when measured from node A to node B. simulate this circuit ...
3answers
308 views

### What does “the resistance looking into” mean?

See this circuit, from Sedra & Smith microelectronics, 6th edition, page 287: It says that the resistance between the gate and source looking into the source is 1/gm, but that the resistance ...
2answers
202 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 ...
2answers
152 views

### How should I connect four resistors to double the capacity with the same resistor? [duplicate]

I know that putting two resistors in parallel will double the wattage from the input to output, but only with half the resistance. Example Parallel Circuit: simulate this circuit – ...
3answers
278 views

### Overcoming a wire's internal resistance?

Let's say I have a very sensitive device that needs EXACT voltage. Let's say that the voltage it requires is 5 volts. Now let's say I'm running the aforementioned voltage over a wire with an ...
1answer
88 views

### ESR and CSR of Capacitor

I'm trying to spec out an output capacitor for a TPS7201 voltage regulator (http://www.ti.com/lit/ds/symlink/tps7201.pdf). It needs to be selected carefully as it is used to stabilize the internal ...
2answers
117 views

### Current flow in series circuit with different (unknown) resistances

I have a question about the current flow in a series circuit. In a series circuit the current flow is the same. It is also true that the current flow is inversely proportional to the amount of ...
7answers
1k views

### If voltage is measured between two points on a wire, with no resistance in between is the voltage zero?

I have a series circuit. Let's say the battery has a potential difference of 10 Volts. On two points of the wire before the current hits any resistors, I attach ...
2answers
96 views

### Is a negative resistor a superconductor that does not require being cooled down to get 0 resistance?

Title explains it, is it possible to create a superconductor using negative resistor oscillator / amplifier? As superconductors are conductors with 0 resistance. Isn't an amplifier a superconductor? ...
4answers
193 views

### Can a speaker be damaged but not blown?

If one plays too loud of a sound through a speaker, it can blow - i.e. become visibly torn or stop working entirely. However is it possible that the loud sound will damage it partly and result in the ...
1answer
68 views

### check resistance is bigger then a constant?

As a part of a bigger project, I want to build an high resistance detector that will respond with a logical pulse 0- under 50KΩ 1- more then ...
0answers
65 views

### Small-signal input and output resistances of the circuit

I am given this circuit: And I am trying to determine the small-signal input and output resistances. I was either given or found all the following info for the circuit: VA = 110V β = 115 T = ...
2answers
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### How to find τ in these circuits?

I know that $τ = \frac{L}{R}$, but what is $R$ in this formula? It seems to be the total resistance, but how to find it in the schematics?
2answers
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### Resistance between data/Addr pins and GND ranges from 1k to 1M, is this normal?

After soldering a 132-pin surface mount DSP, I checked if there are short circuits or not using "GreenLee DM-110" multimeter. I found that the resistance between data or address pins and GND ranges ...
1answer
66 views

### Estimated impedance of a 12V bleeper?

The bleeper(buzzer) I am using is rated for 12 volts DC. It is a piezo electric bleeper and the frequency is created by an internal oscillator. I am not aware with the functioning of peizo electric ...
1answer
164 views

### How do i decide resitance of a DC solenoid valve?

I am designing a circuit for a solenoid valve from BIO-CHEM.SOLENOID VALVE.My product number is 075P2N024-02SQ. I want to know the resistance of valve in order to decide how big a resistance i should ...
1answer
89 views

### Relay resistance

Excuse the crude ms paint drawing. The above is based on an actual relay whose coil has a resistance of 320 ohms. The common to normally closed contact has a resistance of near zero. When the switch ...
2answers
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### basic math question about voltage, ohms, resistance

total n00b here. After working on several projects by copy & paste from other people's schematics and code, I'm finally digging in and learning some of the math to know what I'm doing. If I have ...
1answer
582 views

### calculating resistance for LED strips to use as parking lamps and turn signals

I'm installing LED strips in my car's tail lamps to convert it from conventional bulbs to LEDs. I have a understanding of what I'm doing but not the complete knowledge to make the circuit work ...
1answer
204 views

### At what frequency will the reactance of a 1μF capacitor equal to the resistance of a 2kΩ resistor?

Here is my work: $R = 2000 \Omega$ $X_L = 2 \pi f L = 2 \pi (1 \mu F) f = 6.28\mu F(f)$ $f = \dfrac{2000 \Omega}{6.28 \mu F} = 318.471MHz$ Does this look right to everyone?
2answers
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### how many resistance do i need to safe the LED of PC814?

if i have a input of 5v (arduino HIGH) on the LED of a PC814, how is the value of the resistance that i must use before that, so i don't burn the led? ...
1answer
82 views

### Replicate thermistor behavior for second sensor

I'm working with an R/C electric motor that has a 10K thermistor sensor built into it, which is connected to a speed control that has basic thermal protection. I would like to build a secondary sensor ...
2answers
328 views

### Hardware to Detect EMG or Skin Resistance

I have been given assignment to design a device that can detect emg signal of Skin Resistance change while moving fingers. actually i need to track finger movements using some hardware containing ...
1answer
165 views

### Measuring very small changes in resistor network using current source

I am trying measure a very small change in resistance (approximately .400 Ohms), due to the the effects of connecting a large resistance in parallel with a network of smaller resistors essentially ...
3answers
165 views

### Selectable Voltage Divider Optimal Switching Point

I've built a circuit to measure an unknown resistance (over a large range) which is basically the following: simulate this circuit – Schematic created using CircuitLab Range_Select_1 and ...