# Physics - Recall for Chapter 8; Current and Charge

## Recall Questions

Define current?

Rate of flow of charge.

Define the coulomb?

The SI unit of electrical charge. One Coulomb is defined as the amount of charge that passes in 1 second when the current is 1 ampere.

What do we mean when we say charge is quantised?

It can only take certain values (always $ne$).

If $n$ electrons are removed from a neutral object, what is its charge?

What is an electrolyte?

A liquid containing charged ions.

What is a metallic conductor?

A material comprising a lattice of positive ions and delocalised electrons that carry electrical current.

Which direction does conventional current flow in a circuit?

From positive to negative.

What direction do electrons flow in a circuit?

From negative to positive.

How is an ammeter connected?

In series.

What is the resistance of an ideal ammeter?

$0$ - Ammeters have very small resistance so they have a negligible potential difference across them.

State Kirchoff’s first law (long)?

At any point in a circuit, the sum of the currents entering that point is equal to the sum of the currents leaving.

What is Kirchoff’s first law an example of the conservation of?

Charge.

What is $n$ in the equation $I = nAve$ and what are its units?

Number density of free charge carriers, $m^{-3}$.

What is $A$ in the equation $I = nAve$?

Cross-sectional area of the conductor.

What is $e$ in the equation $I = nAve$?

The elemntary charge ($1.6\times 10^{-19}$)

What is $v$ in the equation $I = nAve$?

The drift velocity of the charge carriers.

What is a conductor?

A material with a large number density of charge carriers.

What is an insulator?

A material with a low number density of charge carriers.

What is a semiconductor?

A material with an intermediate number density of charge carriers.