Current and Charge



Charge carriers are a charged particle. Current in a circuit is induced by the flow of these charge carriers. Current is defined as the rate of flow of charged particles in a wire or component.
In a metal the charge carrier is an electron which is free to move around the molecule colliding with each other and positive ions within the metal.
In a salt solution the charge carrier is a ion, an ion is a charged atom or molecule.

Convention of current
Originally before the discovery of electrons it was believed that current flowed from positive to negative within the circuit, when in fact its negative to positive. (This is because electrons are negative being repelled by the negative side and attracted to the positive side of the cell/battery.)

∆Q = I∆T
I x T = Electrons passing a point in used time
1.6x10^-19

Worked example

A) If the charge flow is 50C and the current is 10A what is the time taken for this amount of charge to pass a point in the circuit?

B) How many electrons pass through the circuit in this time?

Answers
A)
Using equation ∆Q = I∆T

Rearrange it to find time, this is done by dividing the entire equation by the value of current.
This will cancel out current from the right side and divide the value of charge on the left side of the equation. This should look like
∆Q = ∆T
I

50C / 10A = 5 seconds

B)
I x T /1.6x10^-19 = electrons passing a point per value of time


10 x 5 / 1.6 x 10 ^ -19 = 3.125 x 10^20

Physics/Mechanics - How to work out tension in a light inextensible string

Okay guys, best thing to do with this is not to over complicate it so you do not get confused...

Here is a picture of a pulley with 2 attached particles of mass 4kg and 5kg, if the acceleration is 1.09 meters per second per second what is the tension?

Using either of the 2 formulas
If M = largest particle and m = smallest particle
g = gravity which is a constant = 9.8(1)
M x g - M x a = T
m x g + m x a = T

5kg x 9.8N - 5kg x 1.09 = 43.6N
4kg x 9.8N + 4kg x 1.09 = 43.6N

Haii, maths post =]

Ever wondered how to Find the value of X ? when you have a X squared equation?
Well your in luck, i know the answer :P
There is several ways.
I'm going to tell you the method that works without fail..
There is a formula which consists of..
-b +- Squareroot b^2 - 4ac
Divided by 2a
Okay so what are these letters? If the equation is as follows
X^2 + 3x + 2
A = 1 B = 3 C = 2
There is 1 x^2 -- 3 X's -- 2 is the value of the number at the end (the Y intercept)
Plug these into the formula and you should get x = -1 or -2
There is a much faster method but this can be alot more difficult than the formula above
It is called factorising, Simply place the Equation above into 2 different brackets
This is done by having 2 sets of brackets like (x+1)(x+2)=0
that is the factorisation of the equation
Now since the whole thing has to = 0 then X+1 has to equal =, therefore x is -1 and there is the second bracket (it could be the first bracket it makes no difference) (x+2) same thing again, now what is x? X = -2 :)
But how do u factorise? well if you look at the brackets i have made, and expand them yourself you will see that x times x makes the amount of x squareds x times 1 + x times 2 = 3x and 2 x 1 = 2
you just have to figure that out yourself for each equation
An easy way of doing so is start with how many x^2 do i have? in this case 1 so there is going to be 1 x in each bracket, now you need to know the y intercept which is 2 in this case... what times to make 2? 1 and 2 so there the values you place in, these have to also add up the the middle value (the b value)
Enjoy!