4.1- Charge and Current

Define Electric Current

The rate of flow of charged particles.

What is the unit of charge?

Coloumb

What does the elementary charge, e equal to?

approximately 1.602 x 10^-19 coulombs.

What is the net charge of a particle or object quantised by?

It must be a multiple of e.

Define Charge.

• A fundamental property of matter that causes it to experience a force in an electric field.

• Can be positive or negative

• Like charges repel, opposites attract

How does charge flow in metals?

Through the movement of electrons. 

How does charge flow in electrolytes?

Through the movement of ions.

Define ‘conventional current’ .

The flow of ‘positive charge’. Its in the opposite direction to the movement of electrons in the circuit.

How is current in a circuit measured?

With an ammeter that is connected in series with the component.

What is Kirchoff’s first law? 

All the current going into a junction is equal to the current leaving a junction. Therefore charge is conserved. 

What is meant by ‘mean drift velocity’?

The average velocity of the charge carriers due to the applied electric field. It has to be an average because they’re often moving randomly in all directions.

What equation uses drift velocity to calculate current?

I = Anev, where I = current, A = cross sectional area of conductor, n = number density of charge carriers, e = the elementary charge, v = drift velocity. 

Rank: conductors, semiconductors, and insulators from the highest to lowest number density.

Conductors, semiconductors, insulators

Define number density.

The number of free electrons per cubic metre of a material. Greater number density means the material is more conductive.

What would need to happen for a semiconductor to conduct the same current as a metal?

The electrons move faster, therefore the temperature increases.

Why is it that when you turn on a light bulb it lights straight away?

• Free electrons repeatedly collide with the positive ions as they drift through the wire towards the positive terminal​

• The charge carriers generally move very slowly! The electrons from near the switch don't reach the bulb for a long time.​

• The lights turn on quickly because all the free electrons in the wire start moving almost at once (information sent at ~90% of the speed of light).​