8 - Charge and current Flashcards
What is electric charge?
Electric charge is a physical properties that all bodies possess.
Two types of charge:
Positive (+) charge
Negative (-) charge
Bodies with like charge repel and vice versa.
What is the coulomb?
The coulomb (C) is the SI unit of electric charge
1C = the amount of charge that passes per second when there is a current of 1A.
∆Q = I∆t
What is the elementary charge?
All charges are found to be a multiple of the fundamental charge e.
1e = 1.6 x 10⁻¹⁹ (in formula booklet)
What is electric current?
Electric current is the rate of flow of electric charge.
I = Q/t
I = Current (A)
Q = Charge (C)
t = Time (s)
What is the net charge?
The charge on most objects results from either a gain or loss of electrons by the object.
Net charge = ±ne
e = 1.6 x 10⁻¹⁹ (in formula booklet)
What is the difference between conventional current and electron flow?
Conventional current direction: Positive terminal –> Negative terminal
Electron flow direction: Negative terminal –> Positive terminal
Describe electric current in electrolytes is produced.
If a positive electrode (anode) and a negative electrode (cathode) are placed in an ionic solution (e.g sodium cations (Na⁺) and chlorine anions (Cl⁻), ions are attracted to the electrodes.
The movement of ions to their respective electrodes is a flow of charge (i.e electric current).
How are ammeters used to measure current in a circuit?
Ammeters are placed in series in the circuit. Because of this, they should have the lowest possible resistance in order to reduce the effect on the current.
The ideal ammeter has zero resistance –> no effect on current measured –> most accurate
What is the Conservation of charge?
In any closed system, the total charge in the system is conserved.
Conservation of charge stats that electric charge cannot be created nor destroyed. The total amount of charge in the universe (closed system) is constant.
What is Kirchoff’s first law?
At any junction in a circuit, the total current leaving the junction is equal to the total current entering the junction.
What is the number density?
The number density (n) is the number of free electrons per unit volume.
The higher the number density, the greater the number of electrons per m³ and so the better the electrical conductor.
Name and describe the three materials grouped based on number density.
Conductor: Very high number density –> Very high number of conduction electrons.
Semiconductor: Large number density of conduction electrons –> High number of conduction electrons.
Insulator: Number density is almost zero –> Few or no conduction electrons.
Describe the components for alternate equation for electric current.
I = Anev
A: Cross-sectional area of wire
n: Number of charge carriers per m³
e = charge on an electron
v = mean drift velocity
What is the effect of changing cross-sectional area in a wire?
The narrower the wire, the greater the drift velocity must be in order for the current to be the same.
