Chapter 8

Question 1

Current

Equation + units

Answer 1

Rate of flow of CHARGE

thus I = Change in charge / change in time

Columbus / second

Question 2

Elementary charge

Answer 2

1.6 x 10^-19

Question 3

Why is charge quantised

Answer 3

Net charge is +- n x E

Charge is quantised because It csn’t be anything, it is only integer values of e (csn’t be half an e)

Question 4

What carries charge

What are electro,gets

Answer 4

Positive negative ions, electrons

Liquids that can carry current

Question 5

How current go through metal atoms

Answer 5

Metal atoms have delocalised electrons due to metallic binding. This if charge is applied current can go through and connect a circuit

Question 6

Conservation if charge

Answer 6

Charge can not be made or destroyed, total amount in universe is constant

Question 7

Kirchhofs first law

Even if current is leaked?

Answer 7

Sum of current going into a junctions = to sum of current coming out of the junction

• to do with conservation if charge, as current is charge / time, and if current is conserved then charge is conserved as it is not crested here nor destroyed, and total amount is still constant
  Thus
• total number of charge carriers entering MUST = total number if charge carriers leaving
  2) even if current is leaked , earth will give back the current to the circuit, so charge is conserved and Kirchhofs First law stands

Question 8

Denote Kirchhofs First law

Answer 8

E In = EIout

If I1 is positive and I2 is negative then

EI in junction = 0

Question 9

Number density ?

Answer 9

Number density is number of FREE electrons PER cubic metre of material .

Higher number density = higher electrons = better material

Question 10

Classify materials using density how

Copper as example of conductor ?

Answer 10

Insulators like wax = dint allow electronsto move = low number density

Semi conductors like silicon / germanium = let more through so = higher number density

Conductors , lead zinc copper = let a lot through = so highest number density

2) copper and conductors have high magnitudes to order of 10^28

Thus semiconductors have to move faster to reach same current as normal

Question 11

Equation for electric current

Answer 11

I = A (area) N (number density) E (electrical charge ) V (mean drift velocity )

I = ANEV

Question 12

Cross sectional arrea and relationship to mean drift velocity

However?

(Remember )

Answer 12

If I =ANEV

THEN V = I/ANE

SO V = PROPERIONAL TO 1/ A

Such that if you decrease area you mus increase velocity so current is the same, inversely proportional

HOWEVER RESISTANCE WILL INCREASE WITH LESS AREA TOO

3) remember radius will decrease area by squared etc

Question 13

explain the term mean drift be,o it’s of electrons in a metal wire

FULL THREE MARKER

Learn

Answer 13

• The fre electrons make collisions with the positive metal ions in wire, giving them a RANDOM VELOCITY
• free electrons drift towards the Positive end of the supply along the length of the wire
• the distance travelled per unit of time in the length of the wire is called the MEAN DRIFT VELOCITY