CRAC Class C (2025) — Questions 941–950

The resonant frequency is f = 1/(2π√(LC)). A is correct; B/D give the reciprocal (proportional to √(LC)) and C has a squared denominator — all wrong.

For a series LC, Z = R + j(XL − Xc). At resonance XL = Xc so Z is minimum (A). Above resonance XL > Xc → inductive (B); below resonance Xc > XL → capacitive (C). At f = 0 the capacitor is an open circuit, so the series branch is open (D). All four are correct.

For a parallel LC, impedance is maximum at resonance (A). Above resonance the inductor's low reactance shunts the branch → net capacitive (B); below resonance the capacitor is the low-reactance path → net inductive (C). At f = 0 the coil is a short, so the parallel combination is a short (D). All four are correct.

空载Q值 (unloaded Q, Q₀) is the ratio of stored energy to inherent loss with no external load, reflecting coil/cap quality — A is correct. Since capacitor loss is small, Q₀ is dominated by the inductor's Q — B is correct. C is false (a high Q₀ is generally desirable; it is the loaded Q that sets bandwidth), and D is false (the unloaded/loaded ratio is not an arcing criterion).

Quality factor Q = f₀/BW. A higher Q gives a sharper, more selective resonance curve and a narrower bandwidth (A). B describes low Q; C and D wrongly couple Q to frequency stability or operating frequency.

Bandwidth is defined at the −3 dB (half-power) points: the separation between the two frequencies where response falls by 3 dB from the peak. A is correct; the percentages in B/C/D are not the standard definition. 电路元件与符号 Circuit Components and Symbols

The symbol shown in the figure (see [F]LK0497.jpg) is the standard ground (接地) symbol — the horizontal lines decreasing in width. Antenna, resistor, and diode have different schematic symbols, so only A is correct.

Classified by material, common resistors are carbon-film (碳膜), metal-film (金属膜), and wirewound (线绕) — options A, B, C. A damping resistor (D) is a function-specific type, not a material category, so it is not a correct "by material" answer.

Wirewound resistors are explicitly marked with a rated dissipation (power) because they are built to handle high power. Film capacitors, transistors, and ICs are marked mainly with voltage/current/other ratings, not a power-watt figure as prominently. Option A is correct.

The rated power (额定功率) is the maximum power the resistor can dissipate continuously in normal service without damage; the actual dissipated power depends on the circuit. Option A is correct; B/C/D misstate it as a minimum, a fixed consumption, or a supplied power.