Question of the Week - Answer 221017https://learnemc.com/qotw-221017

EMC Question of the Week: October 17, 2022 Faraday's Law says that the sum of the voltages around a closed loop is always equal to zero loop current times resistance loop current times inductance ∂/∂t [magnetic flux passing through loop] Answer The...

Question of the Week - Answer 250331https://learnemc.com/qotw-250331

EMC Question of the Week: March 31, 2025 Which acronym below was commonly used to describe electromagnetic interference decades ago? RMS ELF EMB RFI Answer The best answer is “d.” Long before the acronym EMI entered the lexicon, the term used to...

Question of the Week - Answer 250106https://learnemc.com/qotw-250106

EMC Question of the Week: January 6, 2025 When designing for EMC compliance, it is important to realize that the EMC ground is generally a path for returning currents to their source a conducting body of relatively large extent non-existent above 100...

Question of the Week - Answer 220926https://learnemc.com/qotw-220926

EMC Question of the Week: September 26, 2022 Above the cut-off frequency, the insertion loss of an ideal low-pass pi-filter increases at a rate of 20 dB/decade 40 dB/decade 60 dB/decade 6 dB/octave Answer The best answer is “c.” A pi-filter is a...

Question of the Week - Answer 230220https://learnemc.com/qotw-230220

EMC Question of the Week: February 20, 2023 At high frequencies, which field quantity just above a metal surface has a magnitude approximately equal to the magnitude of the surface current density? magnetic field tangential electric field normal...

Question of the Week - Answer 240506https://learnemc.com/qotw-240506

EMC Question of the Week: May 6, 2024 Suppose the radiated emissions from a product are proportional to the common-mode current on its power cable. Suppose the common-mode current on the cable is proportional to the time-rate-of-change of the voltage...

Question of the Week - Answer 200706https://learnemc.com/qotw-200706

EMC Question of the Week: July 6, 2020 A single-ended 10-MHz digital clock propagating on a circuit board (75-Ω microstrip line) passes through a connector where it transitions to a 100-Ω twisted wire pair. If the peak-to-peak differential voltage on...

Question of the Week - Answer 210315https://learnemc.com/qotw-210315

EMC Question of the Week: March 15, 2021 For a pair of identical circuit board traces over a ground plane, the difference between differential-mode propagation and odd-mode propagation is differential-mode is undefined odd-mode is undefined a factor of...

Question of the Week - Answer 180108https://learnemc.com/qotw-180108

EMC Question of the Week: January 8, 2018 In order to be in the "far-field" of a radiating electromagnetic source, the distance from a point to the source must be greater than a wavelength the largest dimension of the source both "a" and "b" none of...

Question of the Week - Answer 180827https://learnemc.com/qotw-180827

EMC Question of the Week: August 27, 2018 What is the main criteria used to distinguish between electric-field coupling and radiated coupling? source frequency source impedance distance from source to victim in wavelengths minimum size of the source...

Question of the Week - Answer 250623https://learnemc.com/qotw-250623

EMC Question of the Week: June 23, 2025 A shielded cable with twisted wire-pairs carrying high-frequency signals connects to a circuit board mounted in a plastic enclosure with no metal chassis. The circuit board has a solid copper GND/RTN plane. In...

Question of the Week - Answer 210628https://learnemc.com/qotw-210628

EMC Question of the Week: June 28, 2021 At a given frequency between 30 MHz and 1 GHz, what is the lowest common-mode current on a cable attached to a table-top product that is capable of causing an FCC or CISPR Class B radiated emissions failure? 5 A...

Question of the Week - Answer 190520https://learnemc.com/qotw-190520

EMC Question of the Week: May 20, 2019 If the measured radiated emissions at a particular frequency is 44 dB(μV/m) and the limit is 38 dB(μV/m), then the product is over the limit by, 16% 200% 6 dB 6 dB(μV/m) Answer The correct answer is "c". 44...

Question of the Week - Answer 200817https://learnemc.com/qotw-200817

EMC Question of the Week: August 17, 2020 The reason some application notes recommend returning two or more signal currents to a single common point is to give those signals the same zero-volt reference to reduce common-impedance coupling to eliminate...

Question of the Week - Answer 230619https://learnemc.com/qotw-230619

EMC Question of the Week: June 19, 2023 The two-port network illustrated in the attached figure is a low-pass filter high-pass filter band-pass filter band-stop filter Answer The best answer is “c.” The schematic in the figure shows an active band-pass...

Question of the Week - Answer 260330https://learnemc.com/qotw-260330

EMC Question of the Week: March 30, 2026 The voltage waveform on the switch node of a buck converter exhibits ringing. The ringing on the low-to-high transition is different from the ringing on the high-to-low transition as indicated in the figure....

Question of the Week - Answer 220207https://learnemc.com/qotw-220207

EMC Question of the Week: February 7, 2022 A 2-MHz synchronous buck converter is used to convert 12 VDC to 3.3 VDC. The high-side and low-side switches are internal to the converter IC. The inductor is external. The current with the highest time rate...

Question of the Week - Answer 230821https://learnemc.com/qotw-230821

EMC Question of the Week: August 21, 2023 Which two-terminal transient protection device has a V-I curve similar to the one shown in the figure? Avalanche diode TVS diode Varistor Thyristor Answer The best answer is “d.” Two-terminal thyristors have a...

Question of the Week - Answer 170903https://learnemc.com/qotw-170903

EMC Question of the Week: September 3, 2017 The propagation velocity of an electromagnetic wave propagating in a transmission line with an air dielectric is, 3 x 108 meters/sec 377 Ω dependent on the amplitude of the field strength dependent of the...

Question of the Week - Answer 190325https://learnemc.com/qotw-190325

EMC Question of the Week: March 25, 2019 A 3.3-volt, 100 Mbps digital signal is routed across a printed circuit board on a microstrip trace. At the board's edge, it transitions to a twisted wire pair. The characteristic impedance of both the trace and...

Question of the Week - Answer 210726https://learnemc.com/qotw-210726

EMC Question of the Week: July 26, 2021 For a trapezoidal digital signal waveform, the "knee frequency" above which harmonics begin decreasing by 40 dB/decade is 1/(πtr), where tr is the transition time 1/πT, where T is the period (10πtr)/T, where tr...

Question of the Week - Answer 230807https://learnemc.com/qotw-230807

EMC Question of the Week: August 7, 2023 An isolated differential source drives an unbalanced wire pair. One wire in the pair has a 1-mm diameter and the other wire has a 2-mm diameter. If the source supplies 10 mA of current, what is the common-mode...

Question of the Week - Answer 241202https://learnemc.com/qotw-241202

EMC Question of the Week: December 2, 2024 A 2-Ω, 100-MHz clock source drives 4 CMOS inputs on a circuit board over a distance of about 5 cm. The trace impedance is about 75 Ω. Which terminating resistor(s) configuration shown in the figure is...

Question of the Week - Answer 250203https://learnemc.com/qotw-250203

EMC Question of the Week: February 3, 2025 A current filament in free space carries a sinusoidal current, Ic. The intrinsic impedance of free space is η0. The free-space wavelength is λ. If the length of the current filament is ℓ, which equation for...

Question of the Week - Answer 240318https://learnemc.com/qotw-240318

EMC Question of the Week: March 18, 2024 A 24-VDC component has a two-wire power cord and fails to meet its conducted emissions requirement at 360 kHz (the third harmonic of the buck converter on the power input). Two LISNs are employed in the test...

Question of the Week - Answer 250224https://learnemc.com/qotw-250224

EMC Question of the Week: February 24, 2025 Which radiated emissions specification is the most stringent at 100 MHz? FCC Part 15 Class B CISPR 32 Class B MIL-STD-461 RE102 CISPR 25 (automotive) Class 5 Answer The best answer is “c” although a good...

Question of the Week - Answer 200316https://learnemc.com/qotw-200316

EMC Question of the Week: March 16, 2020 The third harmonic of a continuous clock signal shows up as a narrow band peak in a conducted emissions measurement. How does the value measured with an average detector compare to the value measured with a peak...

Question of the Week - Answer 260112https://learnemc.com/qotw-260112

EMC Question of the Week: January 12, 2026 A noise source generates narrow impulses that appear at a constant repetition rate. For measurements in the frequency range from 30 to 1000 MHz with a 120-kHz resolution bandwidth, which of these repetition...

Question of the Week - Answer 210517https://learnemc.com/qotw-210517

EMC Question of the Week: May 17, 2021 The connection inductance of an 0603 SMT decoupling capacitor that is well-mounted to a printed circuit board 2 or 3 layers above the power/ground plane pair is typically a couple nanohenries hundred picohenries...

Question of the Week - Answer 221024https://learnemc.com/qotw-221024

EMC Question of the Week: October 24, 2022 The inductance of a tightly wound coil of wire with N turns is approximately proportional to N N2 wire radius coil radius Answer The best answer is “b.” The inductance of a coil of wire is approximately...

Question of the Week - Answer 201019https://learnemc.com/qotw-201019

EMC Question of the Week: October 19, 2020 When driving a CMOS load (capacitive termination), overshoot and ringing on an otherwise good digital waveform is a clear indication that the _______ has not been properly controlled. connection inductance...

Question of the Week - Answer 180423https://learnemc.com/qotw-180423

EMC Question of the Week: April 23, 2018 Decreasing (speeding up) the transition time in a power inverter's switching components, reduces the losses in the switch generally reduces the electric-field coupling from the switching circuit generally...

Question of the Week - Answer 250324https://learnemc.com/qotw-250324

EMC Question of the Week: March 24, 2025 Which of these two-port networks is fully characterized by its S-parameters? (a) (b) (a) and (b) (a) and (b) and (c) Answer The best answer is “a.” If the S-parameters were determined by driving each of these...

Question of the Week - Answer 210524https://learnemc.com/qotw-210524

EMC Question of the Week: May 24, 2021 In order to function effectively, an EMC ground structure should be connected to the earth electrically small relatively big all of the above Answer The best answer is “c.” To take advantage of the EMC ground...

Question of the Week - Answer 170814https://learnemc.com/qotw-170814

EMC Question of the Week: August 14, 2017 When laying out power electronics circuits, it is important to identify the switching current loop. The switching current loop always passes through the inductor always passes through the switch always passes...

Question of the Week - Answer 191125https://learnemc.com/qotw-191125

EMC Question of the Week: November 25, 2019 If a pre-amplifier is used to pull a signal up out of the noise floor of a spectrum analyzer, it is important that the pre-amplifier is shielded is cooler than the spectrum analyzer has a lower noise figure...

Question of the Week - Answer 210830https://learnemc.com/qotw-210830

EMC Question of the Week: August 30, 2021 A circuit board sends a signal down an unshielded twisted wire pair as illustrated in the figure. The differential-mode characteristic impedance of the wire pair is 100 Ω. The common-mode characteristic...

Question of the Week - Answer 220110https://learnemc.com/qotw-220110

EMC Question of the Week: January 10, 2022 At 10 MHz, the internal inductance of a #24 copper wire is more than 100 nH/m about 50 nH/m negligible undefined Answer The best answer is “c.” At MHz frequencies and higher, the internal inductance of a wire...

Question of the Week - Answer 200824https://learnemc.com/qotw-200824

EMC Question of the Week: August 24, 2020 In a multiwire transmission line, parallel signal conductors with the same impedance to ground carry currents I1 and I2, respectively, where I1 and I2 point in the same direction. The differential current on...

Question of the Week - Answer 260309https://learnemc.com/qotw-260309

EMC Question of the Week: March 9, 2026 A shielded cable connects to a circuit board mounted in a plastic enclosure. To minimize EM emissions and maximize EM immunity, the cable shield should generally connect to the circuit board ground planes...

Question of the Week - Answer 180101https://learnemc.com/qotw-180101

EMC Question of the Week: January 1, 2018 Twisting a pair of parallel wires, increases the characteristic impedance of the transmission line decreases the characteristic impedance of the transmission line increases the inductance per unit length of the...

Question of the Week - Answer 210712https://learnemc.com/qotw-210712

EMC Question of the Week: July 12, 2021 A ferrite toroid with signal wires wrapped in the direction indicated in the figure, serves as a common-mode choke a differential-mode choke an ideal transformer a DC block Answer The correct answer is “a.”...

Question of the Week - Answer 241223https://learnemc.com/qotw-241223

EMC Question of the Week: December 23, 2024 Which parameter of the connection between a decoupling capacitor and the power planes is most important to consider when attempting to optimize the high-frequency performance of the decoupling capacitor?...

Question of the Week - Answer 251027https://learnemc.com/qotw-251027

EMC Question of the Week: October 27, 2025 A differential signal propagates on a pair of microstrip traces then transitions to a twisted wire pair when it leaves the circuit board. Which of the following would cause a differential-mode to common-mode...

Question of the Week - Answer 240715https://learnemc.com/qotw-240715

EMC Question of the Week: July 15, 2024 A 2-meter coaxial cable is used to convey a single-ended 100-Mbps digital signal between two circuit boards in a system. The signal integrity is good, but there is a 10-ampere DC current flowing on the cable...

Question of the Week - Answer 240527https://learnemc.com/qotw-240527

EMC Question of the Week: May 27, 2024 A differential signal propagates on two loosely coupled, parallel microstrip traces. Each trace has a 50-Ω characteristic impedance to the ground plane and the differential-mode impedance is 100 Ω. If the traces...

Question of the Week - Answer 180924https://learnemc.com/qotw-180924

EMC Question of the Week: September 24, 2018 A good low-pass filter on a circuit board trace might consist of two shunt capacitors that have approximately the same value and some space between them have approximately the same value and share the same...

Question of the Week - Answer 231106https://learnemc.com/qotw-231106

EMC Question of the Week: November 6, 2023 A 12-volt DC motor driver is laid out on a circuit board in a plastic enclosure that has a power input connector and a motor cable connector. To minimize EM emissions, the two connectors should be located over...

Question of the Week - Answer 240311https://learnemc.com/qotw-240311

EMC Question of the Week: March 11, 2024 A device-under-test consists of a 10-cm by 10-cm circuit board in a plastic enclosure with an attached power cord. A DC-to-DC converter on the board operating at 1 MHz is responsible for a radiated emissions...

Question of the Week - Answer 230828https://learnemc.com/qotw-230828

EMC Question of the Week: August 28, 2023 The circuit board ground layout shown in the figure is recommended for boards without a nearby chassis. This is a classic example of partitioning (zoning) decoupling a Faraday cage poor design advice Answer The...