Resistance Definition and 1000 Threads

Homework Statement An object falls under gravity and air resistance force bv. It is known there is a characteristic time τ=m/b such that the object comes close to the terminal velocity for t>>τ. Derive an exact expression for the distance d traveled at time t. Homework Equations not sure...

Hello everyone. I have what is probably a relatively simple question. I'm trying to calculate the resistance between two rectangular copper plates submerged in water. I found this thread that briefly discusses it...

Homework Statement In a household, the wife reads a book that uses a light bulb that has a resistance of 100Ω and is connected to a 100 V line while the husband watches a TV that draws 100 W of power. They do these actives for 200 mins. Power comes from a wind generator that charges batteries...

Homework Statement Consider having a battery, its voltage let's say 20 volts. If you connect this battery to a wire. Its resistance is zero. If you precisely measure the voltage at the end of the wire, Would it equal 20 volts or no? Homework Equations dV = I R The Attempt at a Solution Well...

i want to ask how flow resistance of connected tubes with different diameters is calculated. as you see in the uploaded image we imagine that there are 3 tubes. tube A is 2 meters long and cross section area is 2S. tube B is also 2 meters long but first 1 meter has 2S surface area and last 1...

Homework Statement Homework Equations 1/Rt = 1/R1 + 1/R2 + ... The Attempt at a Solution I can do part (i) okay. It is simply 1/12 + 1/12 = 1/6, so R = 6. But I have been trying for ages to figure out part (ii). I tried re-drawing the circuit in different forms but it didn't help me...

Homework Statement In the picture below, is a circuit of constant direct current. The receiver is made of a changable resistor with resistance R. If the reciever delivers maximum electrical power its resistance is a)9 b)6 c)3 d)1.5 e)0.5 Homework Equations Im having trouble finding the equation...

Homework Statement A circuit is setup with an ideal ammeter connected across the 4.0 ohm. What will the reading of the ammeter be? 2. The attempt at a solution I am not sure whether the question is testing my understanding on how an ammeter should be connected in a circuit or about how to...

Given that the resistance of each resistor is 1.0 ohm, find the effective resistance between P and Q. I do not know how to simplify the circuit. A little help on how to redraw the circuit such that the Reff can be calculated is appreciated.

Homework Statement A battery with an emf of 60 V and an internal resistance (r) is connected to a 10 ohm external resistance. The power lost inside the battery is 50w. The same battery is then connected to a 4.0 ohm resistance. The power loss is 200w. What is the internal resistance of the...

All the physics classes I've ever had modled object motion as though it where in a vaccuum, becuase air resistance is obviously a pain in the but to account for. Mathmatically how would i account for it? Say after one second of free fall how much of my velocity would be lost due to air? Im...

Homework Statement Reduce the feedback resistance for the following T-Network Homework Equations Basic circuit analysis (Thevenin maybe?) The Attempt at a Solution My first though was to use Thevenin, and actually I've found some book used that method:

Homework Statement From the picture below, calculate the net resistance between points A and B if ##R_1=12## ##R_2=3.75## Homework Equations 3. The Attempt at a Solution [/B] I cannot think of any way but to find the equivalent resistance od ##R_1## and ##R_2## and add them up but since there...

Hello ! I have little problem understanding about how car rolling resistance , wind resistance and angular resistance affect car speed.SPEED is km/h but resistance is in NEWTONS , i don't understand how that force affects car speed , like FORCE (N) converted to speed(km/h or mph) How to find...

Hello experts... I have an experiment pool boiling. The test section filled with DI water, and use thin flat copper as the heater that connected to the power supply. I want to ask how to measure or calculate the heater temperature if I only have the resistance, voltage and current data reading...

Homework Statement I made this problem on my own. resistors are 10 ohms 30 ohms 15 ohms they are in parallel connections between A and B points Voltage across A and B = 12 volts calculate Rtotal Homework Equations 1/ R = 1/ R1 ´+ 1/R2 + 1/R3 The Attempt at a Solution 1/R = 1/10 +1/30 +...

Can somebody confirm if this is correct? I'm trying to use a wye-delta transformation on capacitors to solve for equivalent capacitance, but to be super-precise, I want to put capacitance in terms of resistance. I = C*(dV/dt) V = IR, so I = V/R V/R = C*(dV/dt) (V*dt) = R*C* dV Integrate both...

Hello, I would think that it would, because if the wire is longer there is more of a chance of their being foreign objects interfering, which could cause resistance, right? Or no?

Homework Statement Homogeneous body with the shape of a truncated rotating cone has a base shaped like a circle. The radius of the lower base is R2 = 8 cm and radius of the upper base is R1 = 4 cm. The height h = 8 cm (see figure). Calculate the total electric resistance between the base...

I think about many times for few days, but I still can't find out the correct answer! Maybe my steps are somethings wrong, please advise me! Thanks! A copper rod, 0.4m long and 4.0mm in diameter, has a resistance of 550μΩ at 20℃. Calculate the resistivity of copper at that temperature. If the...

Hi! Well, I'm programming a vehicle's physics, and I have trouble finding a way to calculate Rolling resistance, though i searched a lot. I already have the Traction Force and the Drag Force, but now I need Rolling Resistance. The best thing i found is that Froll = Croll * P, where Croll is the...

Homework Statement A typical electric blanket consumes 50 W of power when operating. What is the overall resistance of the blanket if it is designed to be plugged into a standard powerpoint? Power = 50 watts Voltage = 240 v (standard powerpoint) Homework Equations I (current) = Voltage/...

Homework Statement The overall resistance of the circuit is 12.5Ω. Calculate the value of the resistor labelled R in the circuit. Homework Equations 1/R = 1/R1 + 1/R2 R = V/I The Attempt at a Solution I understand that you use the first equation for parallel resistors and the second to...

Please view the youtube video below: This is not a homework problem. The reason seems rather weird. Though the video seems incomplete, I would like to know the reason why 39.2 Ohms showed up. It seems rather weird. I know that resistance does not depend on the Voltage or the current if I am...

I need this clarified. I've been told that if you have a circuit with a load resistance of 0, but you have a power supply of internal resistance, when you have no voltage coming from the power pack you will still get a current. I don't understand how this works. I've been told its because the...

Homework Statement If I have a current-voltage (y-x) graph for a resistor, I could argue that the reciprocal of the gradient at a point is equal to the resistance of that resistor at that pd across it. However, on a markscheme for an AS level physics paper, they penalised linking gradient to...

The light in a lightbulb is the result of an increase in temperature. This increase is created by both a highter elektrical resistance in the wire and a highter elektric current. But a higher resistance results in a lower elektric current (I) (I=V/R), so it is both increasing and decreasing the...

Homework Statement There isn't really a "problem statement", but more so a conceptual prompt. Say you throw a ball in the air with some velocity V. The work done due to gravity and drag is Mgh + Fdragd. What I don't know how to do (and there is no additional information, the prompt is very...

I've got a rather simple inquiry, but I haven't been able to get a straight answer via Google searches. When evaluating the impedance of an inductor, do eddy currents represent a series resistance through, or a parallel resistance around the ideal inductor? I've read that eddy currents are...

Homework Statement Homework Equations V=IR The Attempt at a Solution [/B] I found that the current around the circuit was 5mA using kirchhoffs law ( i think) If this is true then the T.E.V should be the voltage across the 120ohm resistor which is .6V (120*5e-3). Now I'm stuck and not sure...

I just read that if we have an antenna, then if the radiation resistance in the antenna is small, then the antenna is an inefficient antenna? This seems somehow counter intuitive to me. Could anyone help explain?

Homework Statement http://imgur.com/vUoRrhO [Note: Image copy inserted by moderator] Homework Equations Req for parallel is 1/Req=1/R+1/R... The Attempt at a Solution I have never seen a circuit like this and I'm not sure as to how I would go about calculating it since there is a resistor...

Hello Im looking to build a very small electrical resistance heater. It should produce no more than 1 to 3 degrees of heat. This is for a personal project of mine. I need to know what types of materials I need to use. Id like the device to be both battery powered and plug in. Can anyone...

Homework Statement In the network of sinusoidal current , R2 = 10 ohm , X2 = -30*sqrt(3) ohm. Find the resistance R1 so that voltage U2 is in phase delay behind voltage U for angle alpha = - pi / 6.Homework EquationsThe Attempt at a Solution Z2 = sqrt(R^2 + X2^2) = 20*sqrt(7) ohms fi2 =...

Homework Statement This problem propped in my head yesterday related to a project I'm working on (not homework, I'm not in school, but I thought this was the best place for it) and I just can't figure out how to crack it! If we have a large plate made up of nxn smaller plates, what is the...

Homework Statement These questions are related to an experiment where we had to record the current for varying values of potential difference (10 readings), then repeat the process with the applied potential difference was reversed a) Why is the resistance of a light bulb not constant? b) Does...

So, I'm asked to demonstrate the formulas for finding out the voltage labeled here as ΔU, which I'm given in my project document: I think I would be able to make the demonstrations without any outside help, if only I knew how I'm supposed to interpret this circuit branch in the middle. Is it...

Homework Statement A real battery can be modeled as an ideal voltage source in series with a resistor. A voltmeter with input resistance of ##1000\Omega## measures the voltage of a 1.5V worn out battery as 0.9V. What is the internal resistance of the battery. Homework Equations ##V=IR## The...

Is it always true that if I have any system of resistors and I calculate the resistance between two points, when I decrease the resistance of one resistor, then the resistance measured between the same two points as previously will not increase? I.E if i have lots of resistors between two...

Homework Statement A beam contains 3.95×108 doubly charged positive ions per cubic centimeter, all of which are moving north with a speed of 1.64×105 m/s. What is the magnitude of the current density? Homework Equations J = nev n = electron density e = electron charge v = drift velocity The...

Homework Statement Calculate the thermal resistance of the heat sink required for the regulator of the question above given the information below [from the datasheet] and the data in the table. Max Load Current (Ilm)= 1A Max Ambient Temp (Ta)= 75°C Thermal Resistance Case to Heat (θchs)=...

My professor says resistance depends on, R\quad =\quad \frac { \rho L }{ A } And is defined as, R\quad =\quad \frac { V }{ I } What does she mean? What is the difference? A definition is denoted by \equiv, what is the difference between that and an ordinary equal sign?

Homework Statement Homework Equations Req = [ ( 1 / R1) + ( 1 / R2) +. ...]^-1 (Parallel) Req = R1 + R2 +. . . (Series ) The Attempt at a Solution I tried to simplify the circuit by spreading it out but I guess something is wrong with my simplification since I can't arrive at the correct...

Homework Statement So this was the question: The 60W filament lamp is connected to a 6.0 V battery. The resistance of the lamp in this circuit is 70 Ohms. Explain why this value differs from the value given in (a)(iv) when the lamp is connected to the 230V supply. My answer was: V=IR, P=IV...

Hi, I am just starting out learning about DC curcuits and I have been presented with a formula in my learning materials to calculate the resistance of a 1km length of 0.6mm diameter copper wire. The formula is attached as an image with the Answer 60Ω My question is how would you enter...

Hi Back in 2011 here https://www.physicsforums.com/threads/resistance-between-two-points-in-an-infinite-volume-of-resistive-gas.513388/ the question of the resistance between two points in an infinite volume of resistive gas was raised but petered out without a solution. The solution could be...

Unlike Ohmic resistors the resistance of a semiconductor decreases with temperature...or not. Can a fragment chipped off a diode or some random IC be used to measure this with a multi meter??

Homework Statement The circuit consists of a battery (V0 = 48.0 V) and five resistors (R1 = 111 Ω, R2 = 182 Ω, R3 = 663 Ω, R4 = 334 Ω, and R5 = 465 Ω). Find the current passing through C, D, and G. Homework Equations V=IR The Attempt at a Solution I tried to find the equivalent resistance...

Homework Statement Incandescent bulbs are designed by keeping in mind that the resistance of their filament increases with an increase in temperature. If at room temperature, 100 W, 60 W and 40 W bulbs have filament resistances R100, R60 and R40, respectively, the relation between these...

How does the current is reduced by the resistance. How is the rate of charge flow decrease in the whole circuit if the variable resistor is placed in the middle of the circuit?