Chapter 8 - Charge and current

Question 1

Define Electric current

Answer 1

Rate of flow of charge (A)

Question 2

How should ammeters and voltmeters be set up

Answer 2

ammeter in series, voltmeter in parallel

Question 3

Define the coulomb

Answer 3

Flow of charge when a current of 1 Ampere flows for one second

Question 4

How to produce a negative ion or a positive ion

Answer 4

Increase number of electrons for negative ion, remove for a positive ion

Question 5

how is charge carried in a metal

Answer 5

There is a lattice of positive ions in a metal, surrounded by free electrons. These electrons, that carry the charge, are attracted to the positive end of the metal.

Question 6

How do liquids carry charge and what is the name of these liquids

Answer 6

Electrolytes are liquids that carry charge, more commonly ionic solutions. Contain positive and negative ions.
- when a pair of electrodes (anode+ and cathode-) a placed in the electrolyte cations- are attracted to the cathode and anions+ are attracted to the anode. This produced an electrical current.

Question 7

Conventional flow

Answer 7

rate of flow of charge from the positive to the negative terminal

Question 8

Electron flow

Answer 8

Negative to positive

Question 9

Kirchhoff’s First Law

Answer 9

for any point in an electrical circuit, the sum of the currents entering that point equals the sum of the currents exiting that same point

Question 10

Kirchhoff’s second Law

Answer 10

In a closed loop, the sum of the p.d.’s equals the sum of the e.m.f’s

Question 11

Outline mean drift velocity

Answer 11

When electrons move through a metal they frequently collide with the positive metal ions, resulting in random movement. When a power supply is connected, the free electrons are attracted towards the positive terminal, but they are still colliding with the positive metal ions. So the mean drift velocity is the average distance travelled per unit time along the length of the wire by the electrons, as they collide with the positive metal ions.

Question 12

Number density

Answer 12

Number of free electrons per unit volume

Question 13

Difference between number densities of conductors and insulators

Answer 13

conductors have high number densities, insulators have low number densities

Question 14

Equation for current using number density and mean drift velocity

Answer 14

I = Anev where I is the current, A is the cross sectional area, e is the elementary charge, and n is the number density