Chapter 8: Charge And Current Flashcards
What is the equation for an electric current?
Current = Change in Charge///Change in Time
What is the difference in measure of charge in chemistry and physics?
Relative charge is used to measure the charges of ions in chemistry. In physics, charges are measures in absolutes using the elementary charge
What is the elementary charge of a proton and an electron?
Proton = 1.6 x 10^-19
Electron = -1.6 x 10^-19
How many electrons make up a coulomb?
6.25*10^18 (e)
What is the equation for net charge?
Net charge = +- Numbers of electrons * Elementary Charge
What is the difference between conventional current and electron flow?
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
What is an ammeter used for?
An ammeter is used to measure the electric current at any point in the circuit. It is placed in series
What property of an ammeter makes it appropriate for measuring current?
An ammeter has a resistance close to 0. This is so close that it is negligible
What does Kirchhoff’s first law state?
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
What is electric charge?
Electric charge is a physical property of matter that is a discrete value as they can only have certain values
What is an electric current?
An electric current is the flow of charged particles
How do you make a metal conduct considering its structure?
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
How do you increase current?
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
What is the name of the point at which Kirchhoff’s law is applicable?
Junction
Why are semiconductors conductive?
Semiconductors are conductive because some covalent bonds can be broken to give the lattice structure free electrons
Why are insulators not conductive?
Insulators are not conductive because their bonds require too much energy to break; therefore, there are no free electrons
How is conductivity measured?
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)
What are examples of insulators?
Wax and Rubber
What are examples of semiconductors?
Silicon and Germanium
What are examples of conductors?
Lead, Zinc, and Copper
What is is the relationship between current and number of charge carriers?
As current increases, number of charge carriers increases
Directly Proportional
What is the relationship between current and cross-sectional area?
When current increases, cross-sectional area increases
What is the relationship between current and velocity?
As current increases, velocity increases
Why is resistance decreased the more resistors you put in parallel circuit?
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
What is mean drift velocity?
Mean drift velocity is the average velocity of the charge carriers due to the applied electric field
What is the equation for mean drift velocity?
Current =
(number of charge carriers) **
(Cross-Sectional Area) **
(Velocity) ***
(Elementary Charge)
What is the number density of copper? What is it therefore?
8.5 * 10^28
Conductor
What is the number density of zinc? What is it therefore?
6.6 * 10^28
Conductor
What is the number density of germanium? What is it therefore?
2 * 10^18
Semiconductor
What is the number density of silicon? What is it therefore?
8.7 * 10^15
Semiconductor
