Chapter 8: Charge and Current

What is Electric current?

The rate of flow of charge

What is the equation for current in terms of charge

Current (I) = ΔCharge (Q) / ΔTime (t)

What is charge measured in?

Charge is measured in coulombs (C).

What is one coulomb defined as?

The flow of charge in a time of one second when the current is 1 amp

what is a quantised number?

Quantized means that it is measured in discrete values

What is the charge of ions actually?

A quantisied number - a +2 charge is 2(e)

e = 1.6×10^-19 C

What is the current in metals carried by?

free floating electrons that move through the metal lattice.

What is the current in liquids carried by?

only some liqiuds can carry a current (it is ions that carry the charge)

Which way is the conventional current

From positive to negative terminal in a circuit.

what is the electron flow

the direction the electrons actually move in (opposite of the conventional current) - from negative to positive terminal

What is Kirchhoff’s first law?

for any point in an electrical circuit, the sum of the currents in to that point is equal to the sum of the currents coming out of that point

Kirchhoff’s law is the consequence of what?

the conservation of charge

Charge is a fundamental physical quantity, therefore…

It cannot be created or destroyed

How does random movement occur?

When electrons move through a metal and collide with positive metal ions

How is Mean Drift Velocity defined

the average velocity of the electrons as they travel down the wire, colliding with positive metal ions

What does number density(n) of a material represent?

The numbner of free electrons per unit volume

what would the number density(n) of a conductor look like

high density

When the value of n is lower…

The electrons must travel at faster speeds to carry the same current

How to find the total charge in the wire?

The product of n, e and the volume