Chapter 8, Current and Charge

Question 1

Defining equation for charge?

Answer 1

ΔQ = IΔt (charge = current * time).

Question 2

Unit for charge?

Answer 2

C - Coulomb.

Question 3

Equation for finding net charge from change in electrons?

Answer 3

Q = ne (charge = number of electrons * elementary charge).

Question 4

Does conventional current flow to or from the positive terminal of a cell?

Answer 4

Away from.

Question 5

Do positive ions move towards an anode or cathode?

Answer 5

Towards the negative cathode.

Question 6

What are ammeters and how do you connect one to a circuit?

Answer 6

Ammeters measure electric current and must be placed in series.

Question 7

State Kirchhoff’s first law.

Answer 7

For any point in a closed circuit the sum of the currents into that point is equal to the sum of the currents out of that point.

Question 8

What does number density describe?

Answer 8

The amount of free electrons per cubic meter of a material.

Question 9

Alternative equation for current?

Answer 9

I = Anev (Current = cross section area * number density * elementary charge * mean drift velocity).

Question 10

What is mean drift velocity in a conductor?

Answer 10

The average velocity of an electron along the conductor.

Question 11

What effect on a wire with a current does decreasing the cross sectional area have? (assuming current is constant).

Answer 11

Decreasing cross sectional area means the mean drift velocity must increase, this in turn is likely to increase the temperature of the conductor.