In an equal-arm balance from the early 20th century (Fig. 31.23), an aluminum sheet hangs from one of the arms and passes between the poles of a magnet, causing the oscillations of the balance to decay rapidly. In the absence of such magnetic braking, the oscillation might continue for a long time, and the experimenter would have to wait to take a reading. Why do the oscillations decay? (a) because the aluminum sheet is attracted to the magnet (b) because currents in the aluminum sheet set up a magnetic field that opposes the oscillations (c) because aluminum is paramagnetic
Figure 31.23 (Quick Quiz 31.5) In an old-fashioned equal-arm balance, an aluminum sheet hangs between the poles of a magnet.
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Chapter 31 Solutions
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- Describe the following physical occurrences as events, that is, in the form (x, y, z, t): (a) A postman rings a doorbell of a house precisely at noon. (b) At the same lime as the doorbell is lung, a slice of bread pops out of a toaster that is located 10 1T1 from the door in the east direction from the door. (c) Tell seconds later, an airplane arrives at the airport, which is 10 km from the door in the east direction and 2 km to the south.arrow_forwardT5arrow_forwardA radar used to detect the presence of aircraft receives a pulse that has reflected off an object 9 ✕ 10−5 s after it was transmitted. What is the distance (in m) from the radar station to the reflecting object?arrow_forward
- (a) The distance to a star is approximately 4.94 ✕ 1018 m. If this star were to burn out today, in how many years would we see it disappear? years(b) How long does it take sunlight to reach Earth? minutes(c) How long does it take for a microwave radar signal to travel from Earth to the Moon and back? (The distance from Earth to the Moon is 3.84 ✕ 105 km.) sarrow_forwardScientists are working on a new technique to kill cancer cells by zapping them with ultrahighenergy (in the range of 1012 W) pulses of light that last for an extremely short time (a few nanoseconds). These short pulses scramble the interior of a cell without causing it to explode, as long pulses would do. We can model a typical such cell as a disk 5.0 µm in diameter, with the pulse lasting for 4.0 ns with an average power of 2.0 x 1012 W. We shall assume that the energy is spread uniformly over the faces of 100 cells for each pulse. (a) How much energy is given to the cell during this pulse? (b) What is the intensity (in W/m2 ) delivered to the cell? (c) What are the maximum values of the electric and magnetic fields in the pulse?arrow_forwardA star emits most of the energy it produces in the form of light waves. A spherical spacecraft of radius r = 50 m arrives to investigate the star. It is at a distance of 50 · 10^6 km from the stars center. The spaceship absorbs all the light that hits its surface. The power absorbed by the spacecraft from the star is 10^7 W (assume that the spaceship absorbs all the radiation that hits it). (a) Estimate the force that the EM radiation exerts on the spaceship. (b) What is the intensity (energy per area) of the star’s radiation at the location of the spacecraft? (c) What is the power output of the star? (d) Say that there is second spherical spacecraft a distance d = 10^8 km away, with a radius r = 10 m. If this spacecraft completely absorbs the radiation of the star, what is the power absorbed by the spaceship? [hint: The important area of the spaceship is its circular cross section]arrow_forward
- The switch in the figure is closed on a at time t = 0. What is the ratio εL/ε (a) just after t = 0 and (b) at t = 1.76τL? (c)At what multiple of τL will εL/ε = 0.500?arrow_forward(a) Suppose a star is 7.61 ✕ 1018 m from Earth. Imagine a pulse of radio waves is emitted toward Earth from the surface of this star. How long (in years) would it take to reach Earth? years (b) The Sun is 1.50 ✕ 1011 m from Earth. How long (in minutes) does it take sunlight to reach Earth? minutes (c) The Moon is 3.84 ✕ 108 m from Earth. How long (in s) does it take for a radio transmission to travel from Earth to the Moon and back? sarrow_forwardScientists are working on a new technique to kill cancer cells by zapping them with ultrahigh-energy (in the range of 1.00×1012 W) pulses of light that last for an extremely short time (a few nanoseconds). These short pulses scramble the interior of a cell without causing it to explode, as long pulses would do. We can model a typical such cell as a disk 5.00 μm in diameter, with the pulse lasting for 4.00 ns with an average power of 2.00×1012 W. We shall assume that the energy is spread uniformly over the faces of 100 cells for each pulse. I 1.00×1021 W/m² Submit Previous Answers Part C Correct What is the maximum value of the electric field in the pulse? ΜΕ ΑΣΦ Emax Submit Request Answer Part D ? V/m What is the maximum value of the magnetic field in the pulse? ΜΕ ΑΣΦ Bmax = Submit Request Answer ? Tarrow_forward
- A distant galaxy emits light that has a wavelength of 655.7 nm. On earth, the wavelength of this light is measured to be 660.7 nm. (a)Decide whether this galaxy is approaching or receding from the earth. (b) Find the speed of the galaxy relative to the earth. (Give youranswer to 4 significant digits. Use 2.998 × 108 m/s as the speed of light.)arrow_forwardYour answer is partially correct. A distant galaxy emits light that has a wavelength of 634.5 nm. On earth, the wavelength of this light is measured to be 639.0 nm. (a) Decide whether this galaxy is approaching or receding from the earth. (b) Find the speed of the galaxy relative to the earth. (Give your answer to 4 significant digits. Use 2.998 x 108 m/s as the speed of light.) (a) The galaxy is (b) Number receding 2126000 from the earth. Units m/sarrow_forward(a) The distance to a star is approximately 4.97 × 10¹8 m. If this star were to burn out today, in how many years would we see it disappear? years (b) How long does it take sunlight to reach Earth? minutes (c) How long does it take for a microwave radar signal to travel from Earth to the Moon and back? (The distance from Earth to the Moon is 3.84 x 105 km.) Sarrow_forward
- Physics for Scientists and Engineers: Foundations...PhysicsISBN:9781133939146Author:Katz, Debora M.Publisher:Cengage LearningClassical Dynamics of Particles and SystemsPhysicsISBN:9780534408961Author:Stephen T. Thornton, Jerry B. MarionPublisher:Cengage LearningUniversity Physics Volume 3PhysicsISBN:9781938168185Author:William Moebs, Jeff SannyPublisher:OpenStax