# Okay, I am down to only a few.

1. Mar 1, 2004

### nautica

I feel pretty confident in the rest of the problems and am down to these. I appreciate the help.

16) 2 long straight wires are parallel and carry current in the same direction. the currents are 8 A and 12 A and seperated by 0.4 cm. The mag field in tesla at a point midway between the wires is?

I used B=uI/2(pie)r but did not come up with the right answer.

20) a uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasiing readius. An explanation would be.

My answer is: the charge is poistive and slowing down

21) electrons are going around a circle in a counterclockwise direction. At the center of the circle they produce a magnetic field that is:

My answer: out of the page

24) 2 parrallel wires, 4 cm apart, carry currents of 2 A and 4 A respectively, in opposite directions. The force per unit length on of one wire on the other is:

4 x 10^-5 attractive

26) Units of magnetic field might be:

a) C m/s
b) C s/m
c) C/kg
d)kg/C s
e) N/C m

23) The units of motional emf are:

a) volt/second
b) volt meter/second
c) volt/tesla
d) tesla/second
e) tesla meter^2/second

I dont have a clue on 23 or 26

thanks
nautica

2. Mar 1, 2004

### himanshu121

for P16 u need to consider directions as well it would be difference of the 2

i.e {uI1-uI2}/2 r

Last edited: Mar 1, 2004
3. Mar 1, 2004

### nautica

If I subtract the 12 - 8 I get 4 so

(4pi x 10^-7) x 8 / 2pi x .004 = 2 x 10^-4

this is not a choice, these are the choices

a) 0
b) 4 x 10^-4
c) 8 x 10^-4
d) 12 x 10^-4
e) 20 x 10^-4

4. Mar 1, 2004

### himanshu121

Note concerning units

U know various formula now look for pro 26

what does option a represents charge*velocity but there is no such formula for magnetic field which corresponds to it

Now for option e Force/{charge*length} which correspond to formula

F=q{dl*B}

for pro 23

emf = BdA/dt= T*m^2/s

5. Mar 1, 2004

### himanshu121

u are doing calculation error it should be 16/4=4*10^-4

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