8.3+ 8.4 Kirchhoff's 1st Law, Mean Drift Velocity

Question 1

what is kirchhoff’s 1st law?

Answer 1

• 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. This law is a consequence of the conservation of charge. Charge is a fundamental physical property, which cannot be created or destroyed, so it must be conserved.

Question 2

what is the ‘number density’?

Answer 2

the number of free charge carriers per unit of volume

Question 3

how does the number denisty impact a material?

Answer 3

the greater the number density, the better the electrical conductor

Question 4

what are the 3 groups of materials?

Answer 4

• conductors (10^28)
• semi conductors (10^17)
• insulators

Question 5

what is the formula for current?

Answer 5

I= Anev
* A= area of cross section
* n= number density
* e= elementary charge
* v= mean drift velocity

Question 6

derive the Anev equation

Answer 6

Question 7

what is drift velocity?

Answer 7

the average velocity of the charges moving along a conductor

not uniform journey as collides with positive metal ions

Question 8

what is the realtionship between the cros sectional area and the mean drift velocity?

Answer 8

inversley proprtional
* as the area increases the number of positive metal ion and distrubance for electrons increases and so the mean drift veloity would be smaller

Question 9

explain the term mean drift velocity of electrons in a metal wire

Answer 9

• free electrons make collisions with metal ions to give them a random velocity
• the free electrons drift towards the positive end the supply along the wire
• the distance travelled per unit time along the length of wire is called the mean drift velocity of the electrons

Question 10

Answer 10