Modern Physics
Questions & Answers
3. Two small plastic spheres each have a mass of 2 grams and a charge of -50 nC. They are placed 2 cm apart (center to center). A) What is the magnitude of the electric force on each sphere? B) If one sphere is held in place what is the resulting acceleration magnitude of the other?
7. Find the speed of light in the following. (a) fluorite (b) fused quartz (c) benzene
8. The rainbow of visible colors in the electromagnetic spectrum varies continuously from the longest wavelengths (the reddest colors) to the shortest wavelengths (the deepest violet colors) our eyes can detect. Wavelengths near 655 nm are perceived as red. Those near 515 mm are green and those near 475 nm are blue, Calculate the frequency of li by of light (in Mz) with a wavelength of 555 nm, 515 nm, and 475 nm.
1) [Brownian Motion and Transport Motion] In a living cell, a ball-shaped organelle of radius r = 500 nm and mass of 16.6x10-22 kg undergoes Brownian motion before it encounters a motor protein. Once the organelle is bound to the motor protein, the organelle is transported with a speed v=1.00 μm/s by the motor protein along a linear track. The solution environment of the cell has temperature T=37°C and viscosity ¹-10-³ Ns/m². Suppose you do a one-dimensional measurement of the organelle's position to distinguish the two types of motion. a) Calculate the relaxation time for the organelle. b) Suppose you have an optical microscope that uses blue light. Are you sure that the instrument is able to image the organelle? Give a reason for your answer. c) In case of Brownian motion, what is the root-mean-square speed of the organelle you would expect from your measurement? d) In case of Brownian motion, what is the root-mean-square displacement of the organelle you would expect from your measurement for a period of t = 5.00 s? e) For the transport by a motor protein, what is the root-mean-square displacement of the organelle you would expect from your measurement for the same period of t = 5.00 s?
In a toy model for protein folding a four-residue peptide with two charged residues at both ends has four possible conformations as shown.
3) [Kinematics of Ideal Gases] A 7.00 liter vessel contains 3.50 moles of ideal gas at a pressure of 1.60x10° Pa. Find, (a) the temperature of the gas and (b) the average kinetic energy of a gas molecule in the vessel. (c) What additional information would you need if you were asked to find the average speed of a gas molecule?
5) [Work Done] A weightlifter has a basal metabolic rate of 80.0 W. As he is working out, his metabolic rate increases by about 650 W. a) How many hours does it take him to work off a 450-Calorie bagel if he stays in bed all day? b) How long does it take him if he's working out? c) Calculate the amount of mechanical work necessary to lift a 120 kg barbell 2.00m. d) He drops the barbell to the floor and lifts it repeatedly. How many times per minute must he repeat this process to do an amount of mechanical work equivalent to his metabolic rate increase of 650 W during the exercise? e) Could he actually do repetitions at the rate found in part (d) at the given metabolic level? Explain.
2. The pulser, channels, and summer are all parts of the 3. Filtering, demodulation, and compression are all part of the 4. The scan converter, image memory, and post-processing are all parts of the 5. While most monitors nowadays are flat-screen, the older ones were called C.R.T., which stands for 6. The pulser, among other things, sets the pulse repetition frequency (P.R.F.). What do you, as an operator, do to make the pulser change P.R.F.? Is this a direct or reciprocal relationship? How is P.R.P. affected? 7. What formula can we use to determine the P.R.F. if we know the maximum depth that we're scanning? What unit is used for P.R.F.? What other formula is this very similar to? 8. What is the main difference between transmit power and gain? 9. Pulse delays are necessary for what two transducer functions? codes. When 10. Coded excitation works by creating longer than normal pulses made up of sequences of cycles and partial cycles. These sequences are called coded pulses, or they come back as echoes, the machine passes them through them into short pulses with higher results in a reduction of than a simple pulse would have given. This or improved "signal-to-noise" ratio. and simplifies 11. Which part of the beam former keeps the pulses (to be sent away from the transducer) from being "heard" by the transducer and sent back to the machine? 12. Data that is in numerical or code form for a computer is called waveforms (electrical or sound) is called data. while live streams of 13. Which part of the beam former is responsible for putting together all the echo data from each pulse and preparing the scan line? 14. The process of eliminating unwanted background noise by only accepting echoes whose frequencies fall within the designated bandwidth is called filter, or This is done in which part of the instrument? 15. If our fundamental operating frequency is 5 MHz, but we tell the machine to accept only echoes in the 9-11 MHz bandwidth, what type of filter are we using? 16. What is another common name for demodulation? What are the 2 steps involved in demodulation? 17. If the range of amplitudes received is 40 dB, what does this mean in terms of how much larger the biggest amplitude is compared to the smallest? What would this mean in terms of how much larger the biggest intensity is compared to the smallest? What would the decibel range of intensities be in this case? 18. What does the machine do to reduce these enormous ranges into something smaller that can handle? In which part of the instrument is this done?
1. Put the following components of an ultrasound machine in order of their function:
