RESISTANCE AND CIRCUITS Flashcards
(19 cards)
What is resistivity?
Resistivity (ρ) is a constant that depends on the material of a conductor, defined by the formula R = ρ (I/A).
What is the SI unit of resistivity?
The SI unit of resistivity is the ohm-meter, Ωm.
How is resistance related to resistivity?
R (Ω) = ρ (Ωm) x (I (m) / A (m^2)).
What is the formula for temperature and resistance?
Rt = Ro (1 + 𝛼t) where Rt is resistance at t °C and Ro is resistance at 0 °C.
What does 𝛼 represent in the temperature-resistance formula?
𝛼 is the temperature coefficient of resistance of the material of the conductor, expressed in K^-1.
What happens to the resistivity of metals as temperature approaches absolute zero?
The resistivity of all metals approaches zero as the temperature approaches absolute zero.
What is superconductivity?
Superconductivity occurs when resistivity drops to zero at a transition temperature for certain substances.
What is a characteristic of current in a superconductor?
A current once started in a superconductor will flow indefinitely, as there is no I²R loss.
How can superconductivity be destroyed?
Superconductivity can be destroyed by placing the sample in a sufficiently large magnetic field.
What is the formula for equivalent resistance in a series circuit?
R = R1 + R2 + R3 + … where R is the equivalent resistance.
What is the potential difference in a series circuit?
The total potential difference across several resistors in series is equal to the sum of the potential differences across each resistor.
What is true about current in a series circuit?
The current in every part of the series circuit is the same.
What is the formula for equivalent resistance in a parallel circuit?
1/R = 1/Rt = 1/R1 + 1/R2 + 1/R3 + … where R is the equivalent resistance.
What happens to resistance when additional resistors are connected in parallel?
Connecting additional resistors in parallel decreases the joint resistance of the combination.
What is the potential difference across resistors in parallel?
The potential difference across several resistors in parallel is the same as that across each resistor.
What is true about current in a parallel circuit?
The sum of the currents in the branches is equal to the line current, with current values varying inversely as the resistances.
What are Kirchhoff’s Laws?
Kirchhoff’s Laws are used in the solution of complex circuits.
What does Kirchhoff’s first law state?
The sum of currents directed toward any point equals the sum of currents directed away from that point.
What does Kirchhoff’s second law state?
The sum of the rises of potential around any closed circuit equals the sum of the drops of potential in that circuit.
