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physics
university physics

Questions and Answers of University Physics

If an emf is produced in a dc motor, would it be possible to use the motor somehow as a generator or source, taking power out of it rather than putting power into it? How might this be done?
An ordinary loudspeaker such as that shown in Fig. 27.28 should not be placed next to a computer monitor or TV screen. Why not? Fig. 27.28 (b) B field of permanent magnet Rigid - speaker cone
Is it possible to have a circuit in which the potential difference across the terminals of a battery in the circuit is zero? If so, give an example. If not, explain why not.
The greater the diameter of the wire used in household wiring, the greater the maximum current that can safely be carried by the wire. Why is this? Does the maximum permissible current depend on the
The direction of current in a battery can be reversed by connecting it to a second battery of greater emf with the positive terminals of the two batteries together. When the direction of current is
Why do the lights on a car become dimmer when the starter is operated?
Current causes the temperature of a real resistor to increase. Why? What effect does this heating have on the resistance Explain
A cylindrical rod has resistivity If we triple its length and diameter, what is its resistivity, in terms of p?
Three pairs of parallel metal plates (A, B and C) are connected as ?shown in Fig. Q23.15, and a battery maintains a potential of 1.5 V across ab. What can you say about the potential difference
At the Fermi National Accelerator Laboratory (Fermilab) in Illinois, protons are accelerated around a ring 2 km in radius to speeds that approach that of light. The energy for this is stored in
You can use plastic food wrap to cover a container by stretching the material across the top and pressing the overhanging material against the sides. What makes it stick? Does the food wrap stick to
The free electrons in a metal are gravitationally attracted toward the earth. Why, then, don’t they all settle to the bottom of the conductor, like sediment settling to the bottom of a river?
Discuss the entropy changes involved in the preparation and consumption of a hot fudge sundae.
A member of the U.S. Congress proposed a scheme to produce energy as follows. Water molecules (H2O) are to be broken apart to produce hydrogen and oxygen. The hydrogen is then burned (that is,
What irreversible processes occur in a gasoline engine? Why are they irreversible?
There are a few materials that contract when their temperature is increased, such as water between 0°C and 4°C. Would you expect CP for such materials to be greater or less than CV Explain?
How does evaporation of perspiration from your skin cool your body?
Why is a hot, humid day in the tropics generally more uncomfortable for human beings than a hot, dry day in the desert?
To raise the temperature of an object, must you add heat to it? If you add heat to an object, must you raise its temperature? Explain.
A wire under tension and vibrating in its first overtone produces sound of wavelength λ. What is the new wavelength of the sound (in terms of λ) if the tension is doubled?
The tone quality of an acoustic guitar is different when the strings are plucked near the bridge (the lower end of the strings) than when they are plucked near the sound hole (close to the center of
Both wave intensity and gravitation obey inverse-square laws. Do they do so for the same reason? Discuss the reason for each of these inverse-square laws as well as you can.
Children make toy telephones by sticking each end of a long string through a hole in the bottom of a paper cup and knot-ting it so it will not pull out. When the spring is pulled taut, sound can be
Why do you see lightning before you hear the thunder? A familiar rule of thumb is to start counting slowly, once per second, when you see the lightning; when you hear the thunder, divide the number
An echo is sound reflected from a distant object, such as a wall or a cliff. Explain how you can determine how far away the object is by timing the echo?
The analysis of SHM in this chapter ignored the mass of the spring. How does the spring’s mass change the characteristics of the motion?
As defined in Chapter 7, gravitational potential energy is U = mgy and is positive for a body of mass m above the earth’s surface (which is at y = 0). But in this chapter, gravitational potential
You are told, “Bernoulli’s equation tells us that where there is higher fluid speed, there is lower fluid pressure, and vice versa.” Is this statement always true, even for an idealized fluid?
Air pressure decreases with increasing altitude. So why is air near the surface not continuously drawn upward toward the lower-pressure regions above?
During vigorous downhill hiking, the force on the knee cartilage (the medial and lateral meniscus) can be up to eight times body weight. Depending on the angle of descent, this force can cause a
Why is concrete with steel reinforcing rods embedded in it stronger than plain concrete?
A certain uniform turntable of diameter D0 has an angular momentum L0. If you want to redesign it so it retains the same mass but has twice as much angular momentum at the same angular velocity as
Experienced cooks can tell whether an egg is raw or hard boiled by rolling it down a slope (taking care to catch it at the bottom). How is this possible? What are they looking for?
Part of the kinetic energy of a moving automobile is in the rotational motion of its wheels. When the brakes are applied hard on an icy street, the wheels “lock” and the car starts to slide. What
A four-wheel-drive car is accelerating forward from rest. Show the direction the car’s wheels turn and how this causes a friction force due to the pavement that accelerates the car forward?
When cylinder-head bolts in an automobile engine are tightened, the critical quantity is the torque applied to the bolts. Why is the torque more important than the actual force applied to the wrench
Although angular velocity and angular acceleration can be treated as vectors, the angular displacement θ, despite having a magnitude and a direction, cannot. This is because does not follow the
Two marbles are pressed together with a light ideal spring between them, but they are not attached to the spring in any way. They are then released on a frictionless horizontal table and soon move
In a zero-gravity environment, can a rocket-propelled spaceship ever attain a speed greater than the relative speed with which the burnt fuel is exhausted?
You often hear it said that most of our energy ultimately comes from the sun. Trace each of the following energies back to the sun:(a) The kinetic energy of a jet plane;(b) The potential energy
A compressed spring is clamped in its compressed position and then is dissolved in acid. What becomes of its potential energy?
The potential-energy function for a force F is U = αx3, where is a positive constant. What is the direction of F?
(a) When a large car collides with a small car, which one undergoes the greater change in momentum: the large one or the small one? Or is it the same for both?(b) In light of your answer to part (a),
Walking on horizontal slippery ice can be much more tiring than walking on ordinary pavement. Why?
The moon is accelerating toward the earth. Why isn’t it getting closer to us?
An automotive magazine calls decreasing-radius curves “the bane of the Sunday driver.” Explain?
The principle of the conservation of energy tells us that energy is never lost, but only changes from one form to another. Yet in many ordinary situations, energy may appear to be lost. In each case,
A rock of mass m and a rock of mass 2m are both released from rest at the same height and feel no air resistance as they fall. Which statements about these rocks are true? (There may be more than one
On a friction-free ice pond, a hockey puck is pressed against (but not attached to) a fixed ideal spring, compressing the spring by a distance x0. The maximum energy stored in U0, the spring is the
If there is a net nonzero force on a moving object, is it possible for the total work done on the object to be zero? Explain, with an example that illustrates your answer.
When does a baseball in flight have an acceleration with a positive upward component? Explain in terms of the forces on the ball and also in terms of the velocity components compared to the terminal
When you tighten a nut on a bolt, how are you increasing the frictional force? How does a lock washer work?
You can classify scales for weighing objects as those that use springs and those that use standard masses to balance unknown masses. Which group would be more accurate when used in an accelerating
To push a box up a ramp, is the force required smaller if you push horizontally or if you push parallel to the ramp? Why?
When a car is hit from behind, the passengers can receive a whiplash. Use Newton’s laws of motion to explain what causes this to occur?
On the moon, g = 1.62 m/s2. If a 2-kg brick drops on your foot from a height of 2 m, will this hurt more, or less, or the same if it happens on the moon instead of on the earth? Explain. If a 2-kg
“It’s not the fall that hurts you; it’s the sudden stop at the bottom.” Translate this saying into the language of Newton’s laws of motion?
When a bullet is fired from a rifle, what is the origin of the force that accelerates the bullet?
The head of a hammer begins to come loose from its wooden handle. How should you strike the handle on a concrete sidewalk to reset the head? Why does this work?
Some of the ancient Greeks thought that the “natural state” of an object was to be at rest, so objects would seek their natural state by coming to rest if left alone. Explain why this incorrect
In uniform circular motion, the acceleration is perpendicular to the velocity at every instant. Is this still true when the motion is not uniform—that is, when the speed is not constant?
In uniform circular motion, what are the average velocity and average acceleration for one revolution? Explain.
When a rifle is fired at a distant target, the barrel is not lined up exactly on the target. Why not? Does the angle of correction depend on the distance to the target?
A package falls out of an airplane that is flying in a straight line at a constant altitude and speed. If you could ignore air resistance, what would be the path of the package as observed by the
A ball is dropped from rest from the top of a building of height h. At the same instant, a second ball is projected vertically upward from ground level, such that it has zero speed when it reaches
If A = 0 for a vector in the xy-plane, does it follow that Ax = -Ay? What can you say about Ax and Ay?
If C is the vector sum of A and B, C = A + B, what must be true about the directions and magnitudes of A and B if C = A + B? What must be true about the directions and magnitudes of A and B if C = 0?
A highway contractor stated that in building a bridge deck he poured 250 yards of concrete. What do you think he meant?
A guidebook describes the rate of climb of a mountain trail as 120 meters per kilometer. How can you express this as a number with no units?
Compare the wave functions for the first three energy levels for a particle in a box of width L (see Fig. 40.12a) to the corresponding wave functions for a finite potential well of the same width
(a) A particle in a box has wave function Ïˆ(x, t) = Ïˆ2(x)e-iE2t/„, where Ïˆnand Enare given by Eqs. (40.35) and (40.31), respectively. If the energy of
For a body orbiting the sun, such as a planet, comet, or asteroid, is there any restriction on the z-component of its orbital angular momentum such as there is with the z-component of the
Table 41.3 shows that for the ground state of the potassium atom, the outermost electron is in a 4s state. What does this tell you about the relative energies of the 3d and 4s levels for this atom?
In Example 43.9 (Section 43.4), the activity of atmospheric carbon before 1900 was given. Discuss why this activity may have changed since 1900.
How many 131I atoms are administered in a typical thyroid cancer treatment?(a) 4.2 × 1010;(b) 1.0 × 1012;(c) 2.5 × 1014;(d) 3.7 × 1015.Iodine in the body is preferentially taken up by the thyroid
A proton beam with an 800-GeV beam energy gives an available energy of 38.7 GeV for collisions with a stationary proton target.(a) You are asked to design an upgrade of the accelerator that will
Calculate the energy (in MeV) released in the triplealpha process 3 4He → 12C.
If the annihilation photons come from a part of the body that is separated from the detector by 20 cm of tissue, what percentage of the photons that originally travelled toward the detector remains
Current experiments show that the mass of the Higgs boson is about 125 GeV/c2. What is the ratio of the mass of the Higgs boson to the mass of a proton?
(a) What is the speed of a proton that has total energy 1000 GeV?(b) What is the angular frequency Ï‰ of a proton with the speed calculated in part (a) in a magnetic field of 4.00 T? Use
When they were first discovered during the 1930s and 1940s, there was confusion as to the identities of pions and muons. What are the similarities and most significant differences?
Estimate the energy width (energy uncertainty) of the ψ if its mean lifetime is 7.6 × 10-21 s. What fraction is this of its rest energy?
The wave functions for a particle in a box (see Fig. 40.12a) are zero at certain points. Does this mean that the particle can€™t move past one of these points? Explain.Fig.40.12a (а) х)
One advantage of the quantum dot is that, compared to many other fluorescent materials, excited states have relatively long lifetimes (10 ns). What does this mean for the spread in the energy of the
Do gravitational forces play a significant role in atomic structure? Explain.
Take the size of a Rydberg atom to be the diameter of the orbit of the excited electron. If the researchers want to perform this experiment with the rubidium atoms in a gas, with atoms separated by a
The bonding of gallium arsenide (GaAs) is said to be 31% ionic and 69% covalent. Explain.
If a sodium chloride (NaCl) molecule could undergo an n → n - 1 vibrational transition with no change in rotational quantum number, a photon with wavelength 20.0 mm would be emitted. The mass of a
At a temperature of 290 K, a certain p-n junction has a saturation current IS = 0.500 mA.(a) Find the current at this temperature when the voltage is(i) 1.00 mV,(ii) -1.00 mV,(iii) 100 mV, and(iv)
When a diatomic molecule undergoes a transition from the l = 2 to the l = 1 rotational state, a photon with wavelength 54.3 µm is emitted. What is the moment of inertia of the molecule for an axis
If a person’s entire body is exposed to 5.0 J/kg of x rays, death usually follows within a few days.(a) Express this lethal radiation dose in Gy, rad, Sv, and rem.(b) How much total energy does a
Is it possible that some parts of the universe contain antimatter whose atoms have nuclei made of antiprotons and antineutrons, surrounded by positrons? How could we detect this condition without
A neutral pion at rest decays into two photons. Find the energy, frequency, and wavelength of each photon. In which part of the electromagnetic spectrum does each photon lie?
Given the Heisenberg uncertainty principle, is it possible to create particle–antiparticle pairs that exist for extremely short periods of time before annihilating? Does this mean that empty space
The gravitational force between two electrons is weaker than the electric force by the order of 10-40. Yet the gravitational interactions of matter were observed and analyzed long before electrical
When a π0 decays to two photons, what happens to the quarks of which it was made?
Why can’t an electron decay to two photons? To two neutrinos?
According to the standard model of the fundamental particles, what are the similarities between baryons and leptons? What are the most important differences?
According to the standard model of the fundamental particles, what are the similarities between quarks and leptons? What are the most important differences?
The quark content of the neutron is udd.(a) What is the quark content of the antineutron? Explain your reasoning.(b) Is the neutron its own antiparticle? Why or why not?(c) The quark content of the

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