# What is Current electricity: Definition and 42 Discussions

An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving particles are called charge carriers, which may be one of several types of particles, depending on the conductor. In electric circuits the charge carriers are often electrons moving through a wire. In semiconductors they can be electrons or holes. In a electrolyte the charge carriers are ions, while in plasma, an ionized gas, they are ions and electrons.The SI unit of electric current is the ampere, or amp, which is the flow of electric charge across a surface at the rate of one coulomb per second. The ampere (symbol: A) is an SI base unit Electric current is measured using a device called an ammeter.Electric currents create magnetic fields, which are used in motors, generators, inductors, and transformers. In ordinary conductors, they cause Joule heating, which creates light in incandescent light bulbs. Time-varying currents emit electromagnetic waves, which are used in telecommunications to broadcast information.

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1. ### Current through a circuit when the key is open

The equivalent resistance of the parallel combination is 2.4 ohm. This implies that if the key is closed the total resistance of the circuit = R + r = 2.4 + 0.6 = 3 ohm However, if the key is open, no current flows through the circuit and thus, by Ohm's law (R = V/I), as I tends to 0, R tends...
2. ### I have a question about diodes and the PN junction

Is the PN junction inside a diode what makes the electrical current only flow in one direction and not in the opposite direction? If this is so, why does it happen? Also Why is the P-type material said to have empty holes and the N-type material to have free electrons?
3. ### Calculate Ip: 9V, 120V Transformer Equation

Okay, so according to the transformer equation, VpIp = VsIs In this question, I know I have to calculate Ip. I think given, Vp = 9V, Vs = 120 V Now I don't know what to use in the value of Is. Please help! The answer is 2.32 A.
4. ### Intuition about electromotive force (EMF)

My understanding of emf Let us consider 2 parallel plates with charges (opp. but equal in magnitude) stored on it. When we connect both the plates from the outer side, the electrons from the lower potential (i.e., negatively charged plate) moves to the higher potential (positively charged plate)...
5. ### Variation of electric field and potential along the axis of a cone

Options are at the top of page as a) b) c) d) Answer may more than one. Now since 'a' is distance from the smaller surface of cone so as we move along the axis area will increase,So current charge density will decrease and as we know J=sigma E,E will decrease,but V will remain constant since...
6. ### Reading of a voltmeter having resistance R across a resistance

Homework Statement The potential difference across resistance R carrying current I is V = IR . Now if the potential difference is measured via voltmeter of resistance r , the reading on voltmeter is V' . Prove that V' = Ir/(R+r) . For what value of r does the voltmeter measure true value...
7. ### Calculating resistances via a potentiometer

Homework Statement Figure shows a potentiometer circuit for comparison of two resistances , the balance point with standard resistor R = 10 ohm , is found to be 58.3 , while that with unknown resistance X is 68.5 cm , determine the value of X . b) what might you do if you failed to find the...
8. ### Electric Power - Which formula to use and when?

Homework Statement : [/B] If the length of the filament of a heater is reduced by 10%, the power of the heater: Options are- a) increases by about 9%. b) increases by about 11%. c) increases by about 19%. d) decreases by about 10%. Homework Equations : P[/B]=I2R Or P=V2/R Where P=power...
9. ### EMF of a battery and voltmeter

Homework Statement We have to measure emf of a battery. We have to voltmeters. Each of them when connected alone across the battery, they read V1 = 0.9V and V2 = 0.6V and when both of them are connected to the battery simultaneously, they both read V3 = 0.45V . What is the emf of...
10. ### What's the current from this circuit? Is it a short circuit or not?

Homework Statement Pic A, what's the I2? Pic B, what's the current across a-b ? Homework Equations V = I*R Voltage in series is different, the current is the same Current in parallel is different, the voltage is the same The Attempt at a Solution from Pic A, I found that I1 = 1A, I3 = 1A...
11. ### Confusion about Electro-motive force (EMF)

The definitions of electromotive force of a cell that i have read include: 1.When no current is drawn from a cell,i.e., when the cell is in open circuit, then potential difference between the terminals of the cell is its electromotive force. 2.The electromotive force of a cell is defined as...
12. ### How to see ON/OFF status by using SCT-013 via Raspberry Pi?

Hello, I'm trying to make a project and I have a trouble. The project is 'online monitoring of machine'. I will show ON if machine works and OFF if machine does not work. And the rule is: I can not effect machine by my circuit. So it looks so simple. I bought SCT-013 non-invasive current sensor...
13. ### Meter Bridge: Finding Error in Resistance

Homework Statement Homework Equations How to find error in resistance ? The Attempt at a Solution I found out the resistance without error. But What is the way to figure out an error of an instrument ?
14. ### Doubt on equipotential surfaces

i know that all conductors are equipotential,then how are charges flowing in a conductor?and at times in we say that charges won't flow since two points are equipotential(like in wheat stone bridge we say that charge won't flow across the capacitor/resistor since the ends of the 5th...
15. ### Equivalent Power In series and parallel combination

How can we derive the formula for finding equivalent power in a series and parallel combination of 'n' resistors (with fixed resistance)?
16. ### Electricity Basics: Voltage 220V & Potential Difference

In Indian standard electric supply at homes is of 220V and 50Hz, What is the physical meaning of Voltage 220V? Does Voltage means Potential difference? I know that potential difference(pd) between two points is the work-done per unit charge to move it between the two points. Is 220V the pd...
17. ### Wheatstone bridge -- Why set all 4 resistances equal?

Can someone explain me,why Wheatstone bridge is most sensitive when all four resistances say A,B,C and D are equal?as far as i know condition for Wheatstone Bridge is A/B=C/D.
18. ### How to Solve This Complex Current Electricity Circuit Problem?

Hi friend I am Stuck in a problem. Please help me in solving this. Thank you all in advance. The problem is as follows. https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-xpf1/t1.0-9/10270329_1576533655907072_4352617381833809587_n.jpg...
19. ### Electric Shock Risk From AC Generator: Can You Touch 1 Terminal?

Can one get electric shock by touching only one terminal of AC generator ?
20. ### Electricity: How Current Works

Refer to my third post :) clearer and the picture in my second post
21. ### Resistance of A to B in Current Electricity Homework

Homework Statement Find the resistance between the A and B( image attached)Homework Equations The Attempt at a Solution I could only simplify the diagram to this (2 attached pic) and i can't proceed any further since i can't identy find any parallel or series circuit/
22. ### Current Electricity - current flowing through hand

Current Electricity -- current flowing through hand Homework Statement i)For a layer dry skin 1mm thick, determine the resistance of a 1 cm^2 area of skin. Resistivity of dry skin : 3 x 10^4 ohms m [3.0 x 10^5 ohms ] ii)A person, who is well-earthed, accidentally grabs a wire of...
23. ### Current electricity and circuits

Current electricity... Homework Statement In the circuit shown(please refer to attchment) only thing missing is that the battery has an internal resistance of r. Now When key K1 is closed the ammeter reads I0 whether K2 is open or closed. But when K1 is open the ammter reads I0 /2 when K2 is...
24. ### Archived Simple question on current electricity

Homework Statement Please refer to the diagram(attachment)...the circuit contains two resistors in series of 25 and 15 ohm respectively and there are two batteries of emf 10 V and 5 V respectively ...Only thing missing in the diagram is that both the batteries have internal resistances of 2.5...
25. ### Current Electricity Homework: Rnet~l2/A & Variables

Homework Statement Refer figure Note: ~ stands for proportionality sign and p stands for resistivity. The Attempt at a Solution R=pl/A Rnet~l2/A V is constant across each conductor, so magnitude of electric field must be constant for every case. Since drift velocity depends on electric...
26. ### Three charges in a plane- static and current electricity

Homework Statement An equilateral triangle has sides of 0.11 m. Charges of -8.6, +8.0, and +1.5 µC are located at the corners of the triangle. Find the magnitude of the net electrostatic force exerted on the 1.5-µC charge. Homework Equations kqQ/d^2 The Attempt at a Solution first...
27. ### Static and current electricity

Homework Statement Three resistors, 21, 43, and 73 , are connected in series, and a 0.55 A current passes through them. What is (a) the equivalent resistance and (b) the potential difference across the three resistors? Homework Equations i tried to use EPE/q by putting the equivalent...
28. ### A very annoying current electricity problem

Homework Statement A battery has an emf=6V. The battery is connected in series with an ammeter and a voltmeter. If a certain resistor is connected in parallel with the voltmeter reading decreases by a factor of 3, and the ammeter reading increases by a factor of 3. What is the INITIAL READING...
29. ### Problem 1 on current electricity

Homework Statement the problem is attached to this post Homework Equations Req=1/R1+1/R2+... for parallel and Req.=R1+R2+... for series... Kirchoff's law for Current and Potential to be applied The Attempt at a Solution completely lost ... pls help
30. ### Current electricity and terminals of a cell

when the terminals of a single cell are connected by means of a conducting wire with no resistor component is there a current flow through the wire ? jus started with current electricity have a lot of doubts thanks for any help
31. ### Current Electricity: Why Does Same Current Pass Through Resistors?

why is current always same for series resistances i mean if a current passes through a resistor a then same current will pass through resistor b does the first resistor not reduces current
32. ### Calculating Battery Current in a Parallel-Series Circuit with Resistances

Homework Statement Three resistances of 4,6,12 ohms are connected in parallel and the combination is connected in series with a 4V battery with internal resistance 2 ohms The battery current is what Homework Equations No relevant question. [b]3. The Attempt at a Solution [/b] I...
33. ### Current Electricity Homework: 3V Battery & 30 Ohm Resistor

Homework Statement You are supplied with a 3V battery and a variable resistor of 30 ohms http://img12.imageshack.us/img12/8329/currentv.png" a) Complete the above circuit diagram such that it's possible to obtain a PD between 0 and 3 V between 2 terminals.Mark the 2 terminals as A...
34. ### Current electricity and finding resistances

Homework Statement A millivoltmeter of resistance 5\Omega gives fullscale deflection,when connected across 75mV. Inorder to use this millivoltmeter as an ammeter,a resistance coil with a third terminal C,is connected between terminals A and B ,of the millivoltmeter. When a current of 1.5A...
35. ### Current Electricity: Force Calcs & Plate Impact

[SOLVED] Current Electricity 1. A positively charged particle enters an evacuated region between two parallel plates with an initial horizontal velocity of 29.6 m/s, as shown in the following diagram. The particle has a mass of 35.6 mg and a charge of +8.40 nC...
36. ### How Do You Calculate the Voltage Across a Resistor in a Complex Circuit?

Homework Statement -------R1--------- l l R1=5 ohms ---- V=120 l R2= 11 ohms - R2 R3= 6 ohms l l R4=8 ohms l...
37. ### Current Electricity: Help understanding concept of potential energy

Current Electricity: Help understanding concept of "potential energy" This is not a problem that I need help with. I rambled on and on for 5 minutes with teacher, eventually giving in and pretending that I understood.. http://i80.photobucket.com/albums/j199/pugfug90/CEPE.gif Umm.. Perhaps...
38. ### Calculating EMF and Internal Resistance of a Battery in a Circuit

The question is: A battery drives a current of 3.0 A round a circuit consisting of two 2.0 ohms resistors in parallel. When these resistors are connected in series, the current changes to 1.2A. Calculate: a) the e.m.f of the battery and b) the internal resistance of the battery. Here's how...
39. ### Why Does Current Distribution Vary in Different Electrical Configurations?

INTRODUCTION: I had been doing some current electricity froblems but now and then I'm having some problems with the distribution of current.I'm really confused. I have attached a figure with this thread, in which I've tried to combine all situations of current distribution in which I'm facing...
40. ### Current Electricity: Calculating Power at 0 & 100 Degrees C

I am revising the chapter on current electricity and i came across this question which i got stuck in the last part. It shows a circuit with a thermistor having a resistane of 60k ohms at 100 deg C and 100k ohm at 0 deg C. The termistor is in series witha 12 k ohm resistor There is a voltmeter...
41. ### Animals and Current Electricity

I was glancing at a physics book, and two questions in the electricity section caught my eye. Why does a cow that touches an electric fence experience a mild shock? Why can birds perch on high-voltage lines without being injured? For the second one, I believe it is that their "feet"...
42. ### Static electricity and current electricity .

The distinctions which are thought to exist between static electricity and current electricity are unfounded and , if subjected to a rational examination , patently absurd. Static electricity maybe described as an unequal distribution of charge (either excess positive or negative charge ) on a...