Chapter 8: Charge And Current

Question 1

What is the equation for an electric current?

Answer 1

Current = Change in Charge///Change in Time

Question 2

What is the difference in measure of charge in chemistry and physics?

Answer 2

Relative charge is used to measure the charges of ions in chemistry. In physics, charges are measures in absolutes using the elementary charge

Question 3

What is the elementary charge of a proton and an electron?

Answer 3

Proton = 1.610^-19
Electron = -1.610^-19

Question 4

How many electrons make up a coulomb?

Answer 4

6.25*10^18 (e)

Question 5

What is the equation for net charge?

Answer 5

Net charge = +- Numbers of electrons * Elementary Charge

Question 6

What is the difference between conventional current and electron flow?

Answer 6

Conventional current dictates that the positive charges move from the positive to the negative terminal
Electron flow is the actual movement of electrons from the negative to the positive terminal

Question 7

What is an ammeter used for?

Answer 7

An ammeter is used to measure the electric current at any point in the circuit. It is placed in series

Question 8

What property of an ammeter makes it appropriate for measuring current?

Answer 8

An ammeter has a resistance close to 0. This is so close that it is negligible

Question 9

What does Kirchhoff’s first law state?

Answer 9

Kirchhoff’s first law states that the sum of the currents at a point is equal to the sum of the current off that point in a loop. This is the same with charge as it is also conserved

Question 10

What is electric charge?

Answer 10

Electric charge is a physical property of matter that is a discrete value as they can only have certain values

Question 11

What is an electric current?

Answer 11

An electric current is the flow of charged particles

Question 12

How do you make a metal conduct considering its structure?

Answer 12

The structure of a metal is a regular crystal structure or lattice of positive ions surrounded by a number of free electrons allowing electrons to flow through. If one end of the metal is positive and the other is negative, electrons in the metal will be attracted towards the positive end

Question 13

How do you increase current?

Answer 13

By having a greater number of electrons moving past a given point per second
By having the same number of electrons moving faster through the metal

Question 14

What is the name of the point at which Kirchhoff’s law is applicable?

Answer 14

Junction

Question 15

Why are semiconductors conductive?

Answer 15

Semiconductors are conductive because some covalent bonds can be broken to give the lattice structure free electrons

Question 16

Why are insulators not conductive?

Answer 16

Insulators are not conductive because their bonds require too much energy to break; therefore, there are no free electrons

Question 17

How is conductivity measured?

Answer 17

For a conductor to be more conductive, it must have a higher number of free charge carriers per unit volume. This is known as number density (n/m³)

Question 18

What are examples of insulators?

Answer 18

Wax and Rubber

Question 19

What are examples of semiconductors?

Answer 19

Silicon and Germanium

Question 20

What are examples of conductors?

Answer 20

Lead, Zinc, and Copper

Question 21

What is is the relationship between current and number of charge carriers?

Answer 21

As current increases, number of charge carriers increases
Directly Proportional

Question 22

What is the relationship between current and cross-sectional area?

Answer 22

When current increases, cross-sectional area increases

Question 23

What is the relationship between current and velocity?

Answer 23

As current increases, velocity increases

Question 24

Why is resistance decreased the more resistors you put in parallel circuit?

Answer 24

Resistance in parallel decreases with more resistors as you effectively increase the cross-sectional area of the resistors, making one large resistor with a large cross-section and thus increasing the current. This in turn reduces the resistance

Question 25

What is mean drift velocity?

Answer 25

Mean drift velocity is the average velocity of the charge carriers due to the applied electric field

Question 26

What is the equation for mean drift velocity?

Answer 26

Current =
(number of charge carriers) **
(Cross-Sectional Area) **
(Velocity) ***
(Elementary Charge)

Question 27

What is the number density of copper? What is it therefore?

Answer 27

8.5 * 10^28

Conductor

Question 28

What is the number density of zinc? What is it therefore?

Answer 28

6.6 * 10^28

Conductor

Question 29

What is the number density of germanium? What is it therefore?

Answer 29

2 * 10^18

Semiconductor

Question 30

What is the number density of silicon? What is it therefore?

Answer 30

8.7 * 10^15

Semiconductor