Solving Parallel-Wire Currents: Help Needed

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In summary, when currents in two parallel wires are going in the same direction, they attract each other. When currents are going in opposite directions, the two wires repel each other.
  • #1
ankur29
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I've read that when currents in two parallel wires are going in the same direction, they attract each other. The same text said that when the currents are going in opposite directions, the two wires repel each other. now i can't porve this for myself as i keep making the folowing mistake

can someone have a look at what i doing worng?

please forgive my spelling

http://img29.imageshack.us/img29/7831/currentinwiresattarctor.th.jpg [Broken]
 
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  • #2


For proof see Smythe "Static and Dynamic Electricity" 2nd Ed, Sec 7.19 and 8.01. Take derivative of stored energy. Opposite currents repel.
 
  • #3


ankur29 said:
I've read that when currents in two parallel wires are going in the same direction, they attract each other. The same text said that when the currents are going in opposite directions, the two wires repel each other. now i can't porve this for myself as i keep making the folowing mistake
Don't think in terms of "polarity". The magnetic field from one wire exerts a force on the second wire. Use the right hand rule to find the direction of that magnetic field, then use it again to find the direction of the force that it exerts on the current in the second wire.
 
  • #4
  • #5


Here is a demo:
 
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  • #6


Doc Al said:
Don't think in terms of "polarity". The magnetic field from one wire exerts a force on the second wire. Use the right hand rule to find the direction of that magnetic field, then use it again to find the direction of the force that it exerts on the current in the second wire.

are you speaking of right hand grip rule? do you mean flemings left hand rule if not how would i use grip rule it to find the force? even so if both the wires are carrying current in same direction right next to each othe rmy thumb points in same direction as do my fingers curl in same direction i.e magnetic field lies in same direction :S

sorry if i just sound ignorant/stupid ,i just can't cant get my head around it

ps thanks for all the quick replies
 
  • #7


Yes, use the right hand grip rule or the corkscrew rule or whatever you prefer to find the field direction around one of the wires.The field due to that wire is at 90 degrees to the current in the second wire.Now use the left hand rule to find the force direction on the second wire.
 
  • #8


ankur29 said:
are you speaking of right hand grip rule? do you mean flemings left hand rule if not how would i use grip rule it to find the force?

Here's a diagram of the right hand rule for finding direction of magnetic force.
 
  • #9


ankur29 said:
are you speaking of right hand grip rule? do you mean flemings left hand rule if not how would i use grip rule it to find the force?
Sorry if I wasn't clear. (And thanks to jtbell for providing helpful hyperphysics links.) I always use a "right hand" rule for everything. Makes it simpler (at least to me). To find the direction of the magnetic field from a straight current-carrying wire, use the right hand "grip" rule. Here's an illustration: http://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/magcur.html#c1"

Once you find the magnetic field from wire 1 that acts on wire 2, then use a different version of the right hand rule to find the force. (See the links provided by jtbell.) This is equivalent to Fleming's left hand rule, of course.
 
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  • #10


I didn't even know there was a left-hand rule until seeing this thread. I've always used my right hand for everything. And all the textbooks I've used so far have mentioned only right-hand rules.
 
  • #11


I don't like using those hand rules.They make me look like a total muppet.
 
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1. What is the concept of parallel-wire currents?

The concept of parallel-wire currents refers to the flow of electric current through two or more wires that are connected at both ends and have the same voltage across them.

2. How do I solve parallel-wire currents?

To solve parallel-wire currents, you can use Kirchoff's Current Law (KCL) and Ohm's Law. First, apply KCL at each junction to determine the current flowing through each wire. Then, use Ohm's Law to calculate the voltage drop across each wire. Finally, use the total current and voltage drop to calculate the resistance of each wire.

3. What are the challenges in solving parallel-wire currents?

The main challenge in solving parallel-wire currents is keeping track of the different currents and voltages in each wire. It is important to label and organize the wires and junctions to avoid confusion. Another challenge is determining the correct direction of the currents, which can be solved by using a consistent direction convention.

4. Can I use a calculator to solve parallel-wire currents?

Yes, you can use a calculator to solve parallel-wire currents. However, it is important to double-check your calculations and make sure you are using the correct units for current, voltage, and resistance.

5. Are there any real-world applications of parallel-wire currents?

Yes, parallel-wire currents have many real-world applications, such as in electrical circuits and power distribution systems. They are also used in everyday devices like household appliances, computers, and cars. Understanding parallel-wire currents is crucial for designing and troubleshooting electrical systems.

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