Physical Sciences Flashcards
7 cards from real STP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Physical Sciences flashcards as text
What is the primary mechanism by which ultrasound causes tissue heating in therapeutic applications?
Answer: Absorption of acoustic energy converted to heat
Therapeutic ultrasound heats tissue primarily through absorption of acoustic energy, which is converted to thermal energy as the wave attenuates.
Which of the following correctly describes the relationship between photon energy and wavelength?
Answer: E = hc/λ
Photon energy E = hf = hc/λ, where h is Planck's constant, c is the speed of light, and λ is the wavelength.
What does a quality factor (radiation weighting factor) account for in dose calculations?
Answer: The biological effectiveness of different radiation types relative to X-rays
The radiation weighting factor (w_R) accounts for the relative biological effectiveness of different radiation types, converting absorbed dose (Gy) to equivalent dose (Sv).
In flow measurement using the Doppler effect in ultrasound, what does the Doppler shift frequency depend on?
Answer: The velocity of blood, ultrasound frequency, and angle between beam and flow
The Doppler shift Δf = 2fv·cosθ/c, so it depends on the transmitted frequency, blood velocity, speed of sound in tissue, and the angle between the beam and flow direction.
What does the term 'signal-to-noise ratio' (SNR) quantify in a measurement system?
Answer: The ratio of desired signal power to background noise power
SNR is the ratio of the power of the desired signal to the power of background noise, with a higher SNR indicating cleaner, more reliable measurements.
Which property of laser light distinguishes it from ordinary white light?
Answer: Spatial and temporal coherence with monochromaticity
Laser light is highly monochromatic (single wavelength), spatially coherent (all wavefronts in phase), and temporally coherent, unlike incoherent broadband white light.
In radiation dosimetry, what is the purpose of a TLD (thermoluminescent dosimeter)?
Answer: To store absorbed dose as trapped electrons released as light upon heating
TLDs contain crystals (e.g., LiF) in which ionising radiation traps electrons in metastable states; when heated, the electrons recombine and emit light proportional to the absorbed dose.