# Physics - Recall for Chapter 8: Current and Charge

> Source: https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-8-current-and-charge/ · Updated: 2021-08-03 · Tags: physics, school, current-and-charge, recall-questions

## 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??
$$ne$$

##### 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.

##### Roughly how many free charge carriers does a conductor have per $m^3$??
$$10^{28}$$

##### Roughly how many free charge carriers does a semiconductor have per $m^3$??
$$10^{17}$$

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