Flashcards: Electric Current and Circuits — 32 cards

What is electric charge in matter particles?

The electrical quantity carried by matter particles.

What is the quantized value of electric charge?

$q = Ze$

What charge does a proton have?

Charge $+e$.

What charge does a silicon ion Si²⁻ carry?

Charge $-2e$.

What is electric current?

The rate of change of charge through a section.

What is the formula for electric current?

$I = \frac{dq}{dt}$

What is the conventional current direction?

The direction of positive-charge motion.

How does conventional current direction relate to negative charge motion?

It is opposite to the motion of negative charges.

What is the formula for current magnitude with n carriers, charge e, speed v, area S?

$I = envS$

How do you calculate the cross-sectional area of a circular conductor with diameter D?

$S = \pi\left(\frac{D}{2}\right)^2$

What is the formula for carrier drift speed v in terms of current I, charge e, carrier density n, and area S?

$v = \frac{I}{enS}$

What is the approximate value of the drift speed of charge carriers?

About $10^{-5}\ \mathrm{m\,s^{-1}}$

What is the approximate thermal speed of charge carriers?

About $10^{6}\ \mathrm{m\,s^{-1}}$

What is the approximate propagation speed of electrical signals?

About $c = 3\times10^{8}\ \mathrm{m\,s^{-1}}$

What does the quasi-static approximation assume about propagation time τ?

Propagation time τ is negligible compared with characteristic variation time T.

What is the formula for propagation time τ in a circuit of length L and signal speed c?

$\tau = \frac{L}{c}$

What is the ARQS condition relating τ and T?

$\tau \ll T$

How is the characteristic variation period T related to frequency f?

$T = \frac{1}{f}$

What is the ARQS condition expressed in terms of circuit length L, speed c, and frequency f?

$L \ll \frac{c}{f}$

What is the value of $c/f$ at 50 Hz?

$6 \times 10^6\ \mathrm{m} = 6000\ \mathrm{km}$

When is the ARQS valid at 50 Hz in terms of circuit length?

When the circuit length is much smaller than 6000 km.

Below what circuit length is the ARQS generally used at 50 Hz?

Below about 600 km.

What is a node in a circuit?

A point where connected wires meet.

What defines a branch in a circuit?

A portion between two nodes.

What is a mesh in circuit topology?

A closed part not passing the same node twice.

When are two dipoles in series?

When they carry the same current.

When are two dipoles in parallel?

When they have the same voltage.

What does Kirchhoff's node law state in the quasi-static approximation?

The sum of currents entering a node equals the sum leaving it.

What physical principle does the node law express?

Conservation of electric charge.

What does Kirchhoff's mesh law state in the quasi-static approximation?

The algebraic sum of voltages around a mesh is zero.

What is the formula expressing voltage additivity in a mesh?

$U_{AC} = U_{AB} + U_{BC}$

What is the voltage relation for the mesh with the stated orientation?

$u_3 = u_1 + u_2 + u_4$