# Electrons are going around a circle in a counterclockwise direction

```Phys102
Term:123
Online HW-Ch29-Lec01
Q1:
Electrons are going around a circle in a counterclockwise direction. At the
center of the circle they produce a magnetic field that is:
A. into the page
B. Zero
C. out of the page
D. to the left
E. to the right
Ans:
A
Q2:
Two semi infinite long straight wires are parallel and carry current in the opposite
direction. The currents are 8.6A and 17A and the wires are separated by 0.67 cm.
What is the magnitude of the magnetic field in T esla at a point midway between the
wires?
Ans:
𝐵=
𝐵=
&micro;𝑜 𝑖1 &micro;𝑜 𝑖2 &micro;𝑜 (𝑖1 + 𝑖2 )
+
=
4π𝑅 4π𝑅
4π𝑅
4π &times; 10−7 &times; (8.6 + 17)
= 7.64 &times; 10−4 𝑇
0.67
4π &times; 2 &times; 10−2
Q3
The magnetic field a distance 7.74 cm from a long straight current-carrying wire is
18.3 &times; 10−5 T. The current in the wire is:
Ans:
𝐵=
𝑖=
&micro;𝑜 𝑖
2π𝑅
2π𝑅𝐵
&micro;𝑜
=
𝑖 = 70.8 𝐴
2π &times; 7.74 &times; 10−2 &times; 18.3 &times; 10−5
4π &times; 10−7
KFUPM-Physics Department
1
```