# Magnetic field at the center of the loop

#### Heart

Here's the question:
"What is the magnetic field at the center of the loop in the figure?"

OK, the question is really simple and it looks easy. However, when I put in the answer, it's wrong. I tried different methods/formulas but still got the wrong answers. Anyone cares to enlighten me?

First, I used the formula B = I(mju_0)N/2R:
- I is 5A
- mju_0 is 4pi * 10^-7
- N is 1
- R is 0.01 m
The wrong answer was 3.14×10-4 T.

I then tried modified B = (2*10^-7)I/R (I multiplied this equation w/ some whole numbers to account for the multi directions of the field - which I then realized that it was the wrong way) I still got the wrong answers.

I then think, hell, the field might cancel out to zero, which was still wrong. (Obviously, the field was in one direction.)

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#### Heart

Anyone? What I don't get is I cannot treat it as a single loop solenoid? If not then what method should I use?

#### Doc Al

Mentor
It's not just a single loop. Don't neglect the field from the long straight wire.

#### david90

people on this board do not seem to know a lot about electromagnetic. I posted two questions and so far no replies yet.

#### Astronuc

Staff Emeritus
Doc Al provided an answer. We expect students to do their homework.

The key is superposition of two magnetic fields due to the long straight wire and the loop.

Meanwhile, we'll take a look at the other questions.

Last edited:

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