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- Thread starter harshakantha
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In summary, according to Ohm's law, zero current means zero potential difference across a resistor. So the potential at B is the same as at the positive terminal of the battery E2.

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ehild

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What have you learned about electric current and electric potential so far?

ehild

ehild

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Femme_physics

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harshakantha

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I know the basic electronic theories, Ohms law, Kirchhoff's Theorem and etc,

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ehild

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harshakantha said:I know the basic electronic theories, Ohms law, Kirchhoff's Theorem and etc,

You should write them under the title "Relevant equations".

And then show some attempt to solve the problem.

As a first hint: Does any current flow through resistor R2?

ehild

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harshakantha

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ok I think there is no current flowing through the R2

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ehild

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Femme_physics said:

No, it is wrong, it influences the potential difference between C and B.

And "its current" has no sense. It is a voltage source, characterized by its emf (electromotive force).

ehild

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ehild

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Very well, so what do you know about the potential drop across R2?harshakantha said:ok I think there is no current flowing through the R2

ehild

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harshakantha

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before that I think we should calculate the current through the whole circuit

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harshakantha

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ya it's wrong, we need E2 when we calculate potential difference of point "B"

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ehild

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https://www.physicsforums.com/showthread.php?t=158460

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ehild

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harshakantha said:ya it's wrong, we need E2 when we calculate potential difference of point "B"

A point has a potential, and potential difference is established between two points. So it is "potential at B, U

The zero of the potential can be assigned to any point of a circuit. So potential of B means potential with respect to the zero point.

ehild

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harshakantha

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I like Serena

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Just a friendly bit of (unasked) advice.

Ehild is helping you.

See the "Homework Helper" medal?

That means ehild know this stuff quite well

As far as I'm concerned ehild has already shown remarkable patience...

Cheers!

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harshakantha

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ya Serena, he knows how to help people very well :-)

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ehild

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harshakantha

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can u give me a hint to get potential of point B :)

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ehild

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As others might be interested in this thread, I continue.

According to Ohm's law, zero current means zero potential difference across a resistor. So the potential at B is the same as at the positive terminal of the battery E2.

There is current in the closed loop at the LHS of the drawing: KVL can be applied to get it. The potential of B with respect to A is obtained from Ohm's law again. If you know the potential both at B and C the potential difference is just a subtraction.

ehild

According to Ohm's law, zero current means zero potential difference across a resistor. So the potential at B is the same as at the positive terminal of the battery E2.

There is current in the closed loop at the LHS of the drawing: KVL can be applied to get it. The potential of B with respect to A is obtained from Ohm's law again. If you know the potential both at B and C the potential difference is just a subtraction.

ehild

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harshakantha

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Total Resistance = R1+R3 = (120+2200)ohms

consider current through Resister R1 and R3 is "I"

then I=E1/(R1+R3) = 15/(120+2200) = 0.0065A

At point "C" let's assume there to be zero potential

1) by going over R3 we lose -14.3V (0.0065*R3)

2) The E2 power supply adds 9V, leaving us with -5.3V (-14.3V + 9V)

3) no current flows through R2

4) therefor the potential different between point "B" and "C" is 5.3V

is this correct??

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ehild

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Yes, but add for clarity that B is negative with respect to C.

ehild

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harshakantha

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you mean to the final answer?? can you show me how to write the final answer :)

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ehild

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harshakantha said:you mean to the final answer?? can you show me how to write the final answer :)

The answer depends how your teacher defined the potential difference between two points, say B and C. It might be Ub-Uc or Uc-Ub. But it is always correct if you give the absolute value and indicate which point is more positive or more negative than the other one.

ehild

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Femme_physics

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I took on solving it myself and got 5.22V (I realized drawing "I2" was a mistake)

http://img32.imageshack.us/img32/3595/voltagedrop.jpg

http://img32.imageshack.us/img32/3595/voltagedrop.jpg

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- #28

ehild

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You are welcome.. And one more little hint: When doing calculations, do not round the data too early, too much. You rounded the current to two significant digits so the error of the result is 0.1 V. During calculations, keep at least one more significant digits as needed in the final result.

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ehild

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Femme_physics said:I took on solving it myself and got 5.22V (I realized drawing "I2" was a mistake)

Good job! Congratulations!

Just a little hint, the same I said to harshakantha: Do not round off too much during the calculations. That current was 0.00647 with 3 digits. Both of you rounded it to 0.0065 which caused an error of 0.066 V in the voltage in harshakantha's calculation as he multiplied it with the bigger resistance. You used the smaller resistance, so your error is one magnitude less, 0.004 V.

ehild

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Femme_physics

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Thank you ehild, so encouraging! :)

You're right I had a feeling I was rounding too much.

You're right I had a feeling I was rounding too much.

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harshakantha

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Thanks ehild for your advice I'll keep it on my mind, bye...

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harshakantha

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Oh.. thanks Femme_physics for your post, hope to get help again from both of you in future. bye..

Potential difference, also known as voltage, is the difference in electric potential between two points in an electric circuit. It is measured in volts (V) and represents the amount of energy required to move a unit of electric charge from one point to another.

Potential difference can be calculated by dividing the amount of work done in moving a unit of charge between two points by the magnitude of that charge. Mathematically, it is represented as V = W/Q, where V is the potential difference, W is the work done, and Q is the charge.

The unit of potential difference is volts (V). It can also be expressed in other units such as joules per coulomb (J/C) or newtons per coulomb (N/C).

Potential difference can be measured using a voltmeter, which is a device that measures the potential difference between two points in an electric circuit. It is connected in parallel to the circuit and displays the potential difference in volts.

The two main factors that affect potential difference are the amount of charge and the distance between the two points. The greater the charge, the greater the potential difference, and the farther apart the points are, the smaller the potential difference. Other factors such as the type of material and the presence of resistors in the circuit can also affect potential difference.

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