BCS Written EEE (892) flashcards

34 cards. Read the term and the definition here. The deck at the top of this page is optional.

Thevenin equivalent

A linear two-terminal network can be replaced by a voltage source V_th equal to the open-circuit voltage in series with R_th, the resistance seen with independent sources deactivated.

Maximum power transfer theorem

For a DC network, maximum power is delivered to a load when R_L equals the Thevenin resistance R_th; the efficiency at that point is 50 percent.

Superposition theorem

In a linear circuit with multiple independent sources, the total response is the sum of responses to each source acting alone, with other voltage sources shorted and current sources opened.

RLC series resonance

At resonance f₀ = 1/(2π√(LC)), inductive and capacitive reactances cancel; the quality factor Q = (1/R)√(L/C) equals f₀ divided by the bandwidth.

DC machine EMF equation

Generated EMF E = PΦNZ/(60A), where P is poles, Φ is flux per pole, N is speed in rpm, Z is armature conductors, and A is the number of parallel paths.

Transformer EMF equation

The RMS induced EMF per winding is E = 4.44 f N Φ_m, where f is frequency, N is turns, and Φ_m is the peak core flux.

Induction motor slip

Slip s = (N_s − N_r)/N_s, where N_s = 120f/P is synchronous speed and N_r is rotor speed; rotor frequency equals s times the stator frequency.

Transformer maximum efficiency

A transformer reaches maximum efficiency when its variable copper loss equals its constant core loss; this typically occurs near full load for distribution transformers.

Per-unit impedance

Per-unit impedance is actual impedance divided by base impedance, where base impedance equals base voltage squared divided by base power in a three-phase system.

Surge impedance loading

Surge impedance Z_c = √(L/C) for a lossless line; surge impedance loading SIL = V_L²/Z_c is the power at which the line produces no reactive power.

Symmetrical components

Any unbalanced three-phase set can be resolved into positive, negative, and zero sequence components; zero-sequence currents require a neutral return path.

Distance relay zones

Zone 1 typically covers about 80 percent of the protected line with no intentional delay; Zone 2 covers 120 to 150 percent with a time delay; Zone 3 provides remote backup.

Three-phase controlled rectifier

A fully controlled three-phase bridge produces average DC voltage V_dc = 1.35 V_LL cos α, where V_LL is the line-to-line RMS voltage and α is the firing angle.

Buck converter voltage ratio

In continuous conduction mode, a buck converter output voltage equals D times the input voltage, where D is the duty cycle of the switch.

V/f induction motor control

Keeping the voltage-to-frequency ratio constant below base speed maintains constant air-gap flux and thus constant torque capability in a variable-frequency drive.

Thyristor latching current

Latching current is the minimum anode current required immediately after turn-on for the thyristor to remain conducting after the gate pulse is removed.

Second-order percent overshoot

For a standard second-order system, percent overshoot equals 100 times e raised to (−ζπ/√(1−ζ²)), where ζ is the damping ratio.

Routh-Hurwitz criterion

The number of sign changes in the first column of the Routh array equals the number of closed-loop poles in the right half of the s-plane.

Phase margin

Phase margin is 180 degrees plus the open-loop phase at the gain crossover frequency, where the open-loop magnitude equals unity (0 dB).

Strain gauge gauge factor

Gauge factor is the fractional change in resistance divided by the fractional change in length; a quarter-bridge output is approximately one quarter of excitation voltage times gauge factor times strain.

BJT current gain relation

For a bipolar junction transistor, β = I_C/I_B and α = β/(1+β); α is the common-base current gain, always less than unity.

Op-amp virtual short

With negative feedback and ideal infinite open-loop gain, the inverting and non-inverting input voltages are forced equal, even though no physical connection exists.

Full-wave rectifier DC output

A full-wave rectifier with no filter produces average DC voltage 2V_m/π, where V_m is the peak input voltage; the ripple frequency is twice the supply frequency.

De Morgan's theorems

The complement of a sum equals the product of complements, and the complement of a product equals the sum of complements: (A+B)' = A'B' and (AB)' = A' + B'.

JK flip-flop next state

The next state of a JK flip-flop is Q(next) = JQ' + K'Q; when J and K are both 1, the output toggles on each clock edge.

Two's complement range

An n-bit two's complement number represents values from −2^(n−1) to 2^(n−1) − 1; negation is performed by complementing all bits and adding one.

8086 physical address

The 8086 forms a 20-bit physical address by shifting the 16-bit segment register left four bits and adding the 16-bit offset, giving segment × 16 + offset.

Watchdog timer

A watchdog timer resets the processor if firmware fails to clear it within a preset interval, recovering an embedded system from software lock-up.

Nyquist sampling theorem

A band-limited signal with maximum frequency f_max can be reconstructed without aliasing if sampled at a rate of at least 2 f_max samples per second.

Shannon-Hartley capacity

Channel capacity in bits per second equals bandwidth B times log base 2 of (1 + S/N), where S/N is the linear signal-to-noise power ratio.

TCP three-way handshake

A TCP connection is established by exchanging SYN, then SYN-ACK, then ACK segments, synchronizing sequence numbers before data transfer begins.

IPv4 private address ranges

Private IPv4 ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16; they are not routed on the public Internet and require NAT for external access.

PERT expected activity time

PERT estimates activity duration as (a + 4m + b)/6, where a is optimistic, m is most likely, and b is pessimistic; variance is ((b−a)/6)².

Break-even quantity

Break-even quantity equals fixed cost divided by the difference between unit selling price and unit variable cost; at this output total revenue equals total cost.