Module 4 Flashcards
(16 cards)
Define the coulomb:
One coulomb of charge is the amount of charge that passes a point per second when there is a current of one amp. (All charges are a multiple of the elementary charge, e, 1.6 * 10^-19)
What is the equation linking current, charge and time?
I = Q / t
What is the equation linking current, cross sectional area, electron density, elementary charge and drift velocity?
I = Anev
Define the volt:
One volt is the energy transfer per coulomb of charge as charges move between two points on a circuit.
What is potential difference?
Potential difference is the measure of the transfer of energy by charge carriers.
What is E.M.F?
E.M.F, or electromotive force, is the energy transferred to the charge carriers by the cell/battery (is measured in volts like potential difference).
Define resistance:
The resistance of a component is the ratio between the potential difference across a component and the current flowing through it.
State the equation that links work done, charge and E.M.F/potential difference:
V = W / Q
Define Ohm’s law:
For a metallic conductor at a constant temperature the potential difference across the conductor is directly proportional to the current flowing through the conductor.
Which of the following are ohmic conductors:
Resistor, Lamp, Diode, L.E.D
Resistor : Ohmic conductor
Lamp : Non-ohmic conductor
Diode/L.E.D : Whilst it starts showing proportionality on the positive side of the I-V graph, it is still non-ohmic.
What is the equation linking resistivity, cross sectional area, length of wire and resistance?
R = (pl) / A
Define Kirchhoff’s First Law:
The total current entering a junction is equal to the sum of the current leaving the junction.
Mathematically prove that in a series circuit the total resistance is equal to the sum of the individual resistances:
In series circuits, V (Total) = V (1) + V (2) + V (3)…
As V = IR
IR (Total) = IR (1) + IR (2) + IR (3)…
As current is constant in series circuits, I(total) = I(1) = I(2) = I(3)
Therefore, R (Total) = R (1) + R (2) + R (3)…
Mathematically prove that in a parallel circuit the reciprocal of the total resistance is equal to the reciprocal of the sum of the resistances:
I (Total) = I(1) + I(2) + I(3)…
As I = V/R
V/R (Total) = V/R (1) + V/R (2) + V/R (3)…
As voltage is constant in a parallel circuit, V (Total) = V(1) + V(2) + V(3)…
1/R (Total) = 1/R (1) + 1/R (2) + 1/R (3)…
What is Kirchhoff’s Second Law?
In any circuit, the sum of the electromotive forces is equal to the sum of the potential differences around any closed loop.
What is internal resistance and it’s equation:
Internal resistance occurs within the battery/cell. Terminal potential difference is the potential difference across the cell (measured from each of its terminals). The equation linking these two is E = V + Ir or E = I(R + r) where E is the E.M.F and r represents the internal resistance.
