Current & Charge Flashcards
(20 cards)
What is current?
The rate of flow of electric charge
How does charge in an LED light work?
Charge can only flow if the component is connected in a positive to negative direction.
Is charge a vector or a scalar quantity?
(Charge is a fundamental in physics)
It is a scalar - even though it travels from positive to negative terminals charge is described by magnitude alone
Equation for current
I = ▵Q / ▵t
Or
I = P/V
Or
V= IR —> I = V/R
Equation for total charge
▵Q = ne
e = elementary charge
n = number density
Base units for electric charge
A s
What does quantised mean?
Charge is quantised
- It is a multiple of the elementary charge
- All electrons have the charge of 1.6x10-19
- Total/net charge = 1.6x10-19 x n
What is (N)?
Number of unbalanced charges - (number of electrons or charged ions)
Equation to find number density
n = ▵Q/ e
What is Kirchhoff’s first law?
The sum of currents entering a junction is equal to the sum of current exiting a junction
- Conservation of charge
What is number density?
The number of charge carriers per unit volume
n = N/V
N = (Number of unbalanced charges), number of electrons or charged ions
V = Volume (m³)
Units for number density
1/m³ —> m⁻³
What is the relationship between current and velocity?
If charge carriers are travelling at a faster speed, the current will increase
They are directly proportional
What is drift velocity?
The mean velocity of charges along the length of a conductor
Equation for drift velocity
I = nAev (rearrange)
V = I/nAe
v = velocity/speed that electrons or charge carries are moving along the wire
e = elementary charge or charge of the ions
A = cross sectional area
n = number of unbalanced charges/electrons or charged ions
4 factors that affect current
Velocity - as the velocity of the charge carriers increases the current auto increases
Charge - if the charge carriers are ions, they will have a much higher charge than electrons, therefore there’ll be a higher current
Cross sectional area - If the area of the wire increases there will be more space for electrons/charge carries to travel through - therefore a higher current
Number density - more charge carries means a higher current
What causes a PD in an electrolyte/conductor?
The charge carriers in the electrolytes go to their own terminal
Positive ions go to the positive terminal, negative ions go to the negative terminal this causes a potential difference
Direction of electron flow and conventional current
Electron flow - negative to positive
Conventional current - positive to negative
What is number density
How many charge carriers are in a volume
number density (n) = charge carriers (N) / volume (V)
What is drift velocity
The average displacement per unit, time of charge carriers along a conductor (e.g a wire)
I = nAev
V = I / nAe
Velocity = Current / Number density x Cross sectional area x Elementary charge
