Electrical Engineering

[Mugiwara]

I haven't had anything about this subject for 3 years, so I'm a bit rusty.
Maybe someone can help me out with some of my homework?

1: The ends of a length of wire are label a and b.
If the current in the wire is iab = -3A, are the electrons moving toward a or b? How much charge passes through a cross section of the wire in 3 seconds?

Since the current is negative, it means its moving b->a, which means the electrons are moving towards b, because the electrons move the opposite direction of the current. (Correct?)

Not sure about the second part though..
Amperes = Coulombs per second.
A = C/s.
A = -3 Amperes
s = 3 seconds.
The charge of electron is -1.602 x 10^-19 Coulombs.
What do I do with that information?

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2: The current through a particular circuit element is given by i(t) = 10sin(200 * pi * t) Amperes in which t is in seconds and the angle is in radians. a. Sketch i(t) to scale versus time for t ranging from 0 to 15 ms(milliseconds). b. Determine the net charge that passes through the element between t = 0 and t = 10 ms. c. Repeat for the interval from t = 0 to t = 15ms.

No idea about this one o_o

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3: The charge carried by an electron is 1.9 x 10^-19 C. Suppose that an electron moves through a voltage of 120 V from the positive polarity to the negative polarity. How much energy is transferred? Does the electron gain or lose energy?


Thanks for the help in advance :3

 

[Maina Deah]

hehe tough one, my brain is a bit rusty with problem solving but I think I can answer no. 2
when do you need it?

 

[Mugiwara]

hehe tough one, my brain is a bit rusty with problem solving but I think I can answer no. 2
when do you need it?

Friday.
Gonna do it tomorrow at the university with a friend, but I thought I'd get a little head start.

Isn't #2: Just make a graph for the current, i(t) like a function?

 

[99minutes]

For the third one, I think you use the formula: V = W/Q.

Rearrange it to make W (work-done/ energy) the subject. So you get: W = VQ.

W = (120) x (1.6x10^-19)
W = 1.92x10^-17
_____________________________________________
Hope I could help. I love Physics but sorry if I'm mistaken xD
Working on the other ones now :3

 

[99minutes]

#1: You have Current (-3A) and time (3s). They want the charge flowing during that time, not the charge on a single electron.

So: Q = It
Q = -3 x 3
Q = -9 C.

...It seems a bit too easy o__o
And when that happens, you just know you did something wrong xD
___________________________________

I'm confused about #2. I think you have to draw a graph and take readings off there (most likely by drawing tangents where required).

___________________________________
Hope I could help. Sorry if wrong, once again xD
And sorry for double posting.

 

[Mugiwara]

For the third one, I think you use the formula: V = W/Q.

Rearrange it to make W (work-done/ energy) the subject. So you get: W = VQ.

W = (120) x (1.6x10^-19)
W = 1.92x10^-17
_____________________________________________
Hope I could help. I love Physics but sorry if I'm mistaken xD
Working on the other ones now :3

it's 1.9x10^-19
2.28 x 10^-17 is the answer than.
Meaning that the electron gains energy.

#1: You have Current (-3A) and time (3s). They want the charge flowing during that time, not the charge on a single electron.

So: Q = It
Q = -3 x 3
Q = -9 C.

...It seems a bit too easy o__o
And when that happens, you just know you did something wrong xD
___________________________________

I'm confused about #2. I think you have to draw a graph and take readings off there (most likely by drawing tangents where required).

___________________________________
Hope I could help. Sorry if wrong, once again xD
And sorry for double posting.

Thats what I was afraid of.. It seemed too easy

But thanks^_^

I'll check with the other students what answer they got.
I had a similar subject 3 years ago and some of the same theme in physics, but I think since it was the first chapter of the book, they made it that easy. But still, its university level, it shouldn't be that easy..

 

[99minutes]

it's 1.9x10^-19
2.28 x 10^-17 is the answer than.
Meaning that the electron gains energy.


Thats what I was afraid of.. It seemed too easy

But thanks^_^

I'll check with the other students what answer they got.
I had a similar subject 3 years ago and some of the same theme in physics, but I think since it was the first chapter of the book, they made it that easy. But still, its university level, it shouldn't be that easy..

Ah, right xD
But you got the main idea. LOL I always screw up the little things.

And you're welcome. Good luck, Pirate King =DD

 

[Mugiwara]

Ah, right xD
But you got the main idea. LOL I always screw up the little things.

And you're welcome. Good luck, Pirate King =DD

Thanks 1 hour 39 minutes!

 

[99minutes]

Thanks 1 hour 39 minutes!

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Lmao xD
Now close this thread before the trolls and spammers roll in D: