4.1 Charge And Current

Question 1

what is electrical current

Answer 1

rate of flow of charge per unit time

the flow of electrons in metals and the movement of ions in electrolytes

Charge (Q) = current (I) x time (s)

Question 2

What is charge and state its unit

Answer 2

Coulomb (C)

Net charge is a positive or negative value where the number given (eg +1) represents a multiple of e

Question 3

what is the elementary charge (e)

Answer 3

Elementary charge (e) = 1.6 x 10 ^-19

Question 4

What is an ion

Answer 4

A charged atom that has gained/lost electrons

Question 5

What are charge carriers

Answer 5

Varies depending on material
Metals - free electrons
Electrolytes (liquids that conduct) - ionic solutions so charge is carried by both + and - ions, they split at the electrodes, generating an electrical current

Question 6

What is conventional current

Answer 6

The virtual movement of positive charge form positive to negative terminals

In reality electron flow is in the opposite direction due to laws of attraction

Question 7

What is Kirchhoff’s 1st law

Answer 7

Total current entering a junction = total current leaving a junction

Because charge is always conserved

Question 8

What is mean drift velocity of charge carriers and why does it exist

Answer 8

The average speed and direction of electrons in a wire

Electrons collide with ions resulting in random movement

Question 9

What is the equation for current, considering mean drift velocity in a wire

Answer 9

Current (A) = number of free electrons per cubic metre x cross sectional area of the wire (m ²) x velocity (ms ^-1) x charge of one electron

I = nAve

Question 10

What is number density (n) and how does it vary

Answer 10

The number of free electrons per unit volume (m ³)

Conductors (metals) - 10 ²⁸ per m ³
Semiconductors (silicon) - in small
Insulators (plastics) - extremely small, near zero