Chapter 8 Charge and Current Flashcards
What is electric current?
rate of flow of charge, measured in Amperes
How is current measured in a circuit?
Ammeters in series
What is charge?
a physical characteristic
What is conventional current?
the flow from positive to negative, direction of current in a circuit
What is a conductor?
a material that allows the flow of electrical charge. Good conductors have a large amount of free charge carriers to carry a current
What are electrolytes?
Substances that contain ions that when dissolved in a solution, act as charge carriers and allow current to flow.
What is electron flow?
The opposite direction to conventional current flow. Electrons flow from negative to positive
What is elementary charge?
The smallest possible charge, equal to the charge of a proton.
What is the value of elementary charge?
1.60 x10^-19C
What are insulators?
A material that has no free charge carriers and so doesn’t allow the flow of electrical charge.
What is Kirchhoff’s First Law?
A consequence of the conservation of charge. The total current entering a junction must equal the total current leaving it.
What is mean drift velocity?
The average velocity of an electron passing through an object. It is proportional to the current, and inversely proportional to the number of charge carriers and the cross-sectional area of the object.
What is the quantisation of charge?
The idea that charge can only exist in discrete packets
of multiples of the elementary charge.
What are semiconductors?
A material that has the ability to change its number of charge carriers, and so its ability to conduct electricity. Light dependent resistors and thermistors are both examples.
What is the equation for current, charge and time?
I = Q/t
How do you calculate the net charge on an object?
Q = +/- ne
What is millikan’s experiment?
Motion of an electrically charged oil droplet between two oppositely charged parallel plates. Oil droplets falling through the air experienced gravitational force, air resistance and upthrust.
What is the structure of a metal?
regular crystal structure OR lattice of positive ions, surrounded by delocalised electrons
What produces a larger current?
- greater number of electrons moving past a given point each second
- same number of electrons moving faster through a metal
What is a positive electrode called?
anode
What is a negative electrode called?
cathode
Why are ammeters placed in series?
so they have the lowest possible resistance, reduce effect of current.
What would happen with an ammeter with high resistance?
decrease the current its measuring
What is an ideal ammeter?
has zero resistance, no effect on the current it measures
What is the conservation of charge?
electrical charge can neither be created nor destroyed, constant in the universe
What is the equation for Kirchhoff’s first law?
sum of current in = sum of current out
What is number density?
number of free electrons per cubic meter of material, higher means better electrical conductor
What are charge carriers?
electrically charged particles, free to move in an object
How fast do charge carriers move?
slowly. free electrons repeatedly collide with metal ions as they drift, when switch on, they start moving all at once
What is another equation from current?
I = A n e V
(area x number density x elementary charge x mean drift velocity)
How are current and wire cross section linked?
current is directly proportional to the cross sectional area of a wire
What happens if you half the radius of a wire?
the velocity of the electrons quadruple
What concepts does Kirchhoff’s first law deal with?
electrical current: any point in an electrical circuit, the sum of the currents into that point = sum of currents out of that point
What does Kirchhoff’s law conserve?
charge
Do semiconductors or metals have a higher number density?
metals
How do make semiconductors carry the same current as metals?
make the electrons move faster
What happens when you switch on a lamp?
charge carriers, like electrons move SLOWLY and free electrons constantly collide with the metal ions and drift to the positive terminal. They start moving at once, so quick light on
What is the other equation for electric current?
I = A n e v
(cross-sectional area x number density x elementary charge x mean drift velocity)
