Chapter 8 - Charge and current

Question 1

what is current

Answer 1

The rate of flow of charge

Question 2

Kirchhoff’s First Law

Answer 2

At any junction in a circuit, the total current leaving the junction is equal to the total current entering the junction

Question 3

what is the charge on an electron

Answer 3

-1.6 * 10 ^-19

Question 4

How many electrons are there in 1 C

Answer 4

6.25 * 10 ^18

Question 5

Equation for charge and current

Answer 5

Q = IT

Question 6

what is the charge of a proton

Answer 6

1.6 * 10^ -19

Question 7

Mean drift velocity equation

Answer 7

I = n a v q
I - current 
n - number of electrons per volume 
a - cross sectional area
v - mean drift velocity 
q - charge on charge carrier 
if q is an electron then it is 1.6 * 10^ -19

Question 8

If there is a larger cross sectional area, how does this affect the velocity

Answer 8

velocity decreases because they are inversely proportional

Question 9

what is mean drift velocity

Answer 9

average velocity that a particle, such as an electron, attains due to an electric field.

Question 10

What is the number density

Answer 10

The number of free electrons per cubic metre of material

Question 11

Do conductors have a very high or low number density?

Answer 11

Conductors have a very high number density.

Question 12

How fast do charge carriers move

Answer 12

In reality, they actually move quite slowly, but the free electrons collide with the positive metal ions, meaning they actually move quite slowly. The reason that lights turn on so quickly is because they all start moving all at once.

Question 13

If the radius of a wire halves how does this affect the mean drift velocity

Answer 13

If the radius halves, the cross sectional area will decrease by a factor of 4. Since the velocity and the area are inversely proportional, this means that the velocity will increase by a factor of 4.