Electric Current and Resistance

Flashcards covering concepts from a lecture on electric current, Ohm's Law, resistance, and electrical power.

What is electric current?

The rate of flow of charge through some region of space.

What is the SI unit of electric current?

The ampere (A)

What is the formula for average electric current?

I_avg = ∆Q/∆t

What is the formula for instantaneous electric current?

I = dQ/dt

What causes charges to flow in a conductor?

An electric field (E)

What creates the electric field in a conductor?

A potential difference

What happens to electrons in a conductor without an external electric field?

They move randomly.

What is the direction of conventional current?

The direction of the flow of positive charges.

Is current a vector quantity?

No, current is a scalar

What does a negative value for current indicate?

The conventional current flows opposite to the indicated direction.

What is the formula relating current (I), charge density (n), charge per particle (q), drift velocity (vd), and cross-sectional area (A)?

I = nqvdA

What is current density (J)?

Current per unit area (J = I/A)

What is the relationship between current density (J), charge density (n), charge per particle (q), and drift velocity (vd)?

J = nqvd

What is the relationship between current density and electric field in ohmic materials?

J = σE, where σ is conductivity

What is Ohm's Law?

The ratio of current density to electric field is a constant (conductivity) for many materials.

What is the formula for resistance (R) in terms of length (l), cross-sectional area (A), and conductivity (σ)?

R = l / (Aσ)

What are the SI units of resistance?

Ohms (Ω)

What is resistivity (ρ)?

The inverse of conductivity (ρ = 1/σ)

What are the SI units of resistivity?

ohm-meters (Ω . m)

How does temperature affect the resistivity of conductors?

Resistivity generally increases with temperature.

What is the temperature coefficient of resistivity (α)?

A measure of how much the resistivity of a material changes with temperature.

Define superconductors:

Materials with zero resistance below a critical temperature (Tc).

What is electrical power (P)?

The rate at which energy is delivered to a resistor.

What is the formula for electrical power in terms of current (I) and voltage (∆V)?

P = I∆V

What is the formula for electrical power in terms of current (I) and resistance (R)?

P = I^2R

What is the formula for electrical power in terms of voltage (∆V) and resistance (R)?

P = (∆V)^2 / R