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university physics

Questions and Answers of University Physics

The laws of optics also apply to electromagnetic waves invisible to the eye. A satellite TV dish is used to detect radio waves coming from orbiting satellites. Why is a curved reflecting surface (a
For the situation shown in Fig. 34.3, is the image distance s' positive or negative? Is the image real or virtual? Explain your answers.Fig.34.3 When n, > n. P' is closer to the surface than P: for
A spherical mirror is cut in half horizontally. Will an image be formed by the bottom half of the mirror? If so, where will the image be formed?
To vary the angle as well as the intensity of polarized light, ordinary unpolarized light is passed through one polarizer with its transmission axis vertical, and then a second polarizer is placed
Next, unpolarized light is reflected off a smooth horizontal piece of glass, and the reflected light shines on the insect. Which statement is true about the two types of cells?(a) When the light is
First, light with a plane of polarization at 45° to the horizontal shines on the insect. Which statement is true about the two types of cells?(a) Both types detect this light.(b) Neither type
Light is incident in air at an angle ua (Fig. P33.54) on the upper surface of a transparent plate, the surfaces of the plate being plane and parallel to each other.(a) Prove that Î¸a =
Light is incident normally on the short face of a 30°-960°-990°- prism (Fig. P33.50). A drop of liquid is placed on the hypotenuse of the prism. If the index of refraction of the prism is
Can water waves be reflected and refracted? Give examples. Does Huygens’s principle apply to water waves? Explain.
Huygens’s principle also applies to sound waves. During the day, the temperature of the atmosphere decreases with increasing altitude above the ground. But at night, when the ground cools, there is
The explanation given in Section 33.6 for the color of the setting sun should apply equally well to the rising sun, since sunlight travels the same distance through the atmosphere to reach your eyes
The indexes of refraction for violet light (λ = 400 nm) and red light (λ = 700 nm) in diamond are 2.46 and 2.41, respectively. A ray of light traveling through air strikes the diamond surface at an
Atmospheric haze is due to water droplets or smoke particles (“smog”). Such haze reduces visibility by scattering light, so that the light from distant objects becomes randomized and images
Light scattered from blue sky is strongly polarized because of the nature of the scattering process described in Section 33.6. But light scattered from white clouds is usually not polarized. Why not?
You are sunbathing in the late afternoon when the sun is relatively low in the western sky. You are lying flat on your back, looking straight up through Polaroid sunglasses. To minimize the amount of
In Fig. 33.31, since the light that is scattered out of the incident beam is polarized, why is the transmitted beam not also partially polarized?fig.33.31 Incident white light, y unpolarized *-
For the old “rabbit-ear” style TV antennas, it’s possible to alter the quality of reception considerably simply by changing the orientation of the antenna. Why?
When unpolarized light is incident on two crossed polarizers, no light is transmitted. A student asserted that if a third polarizer is inserted between the other two, some transmission will occur.
If you sit on the beach and look at the ocean through Polaroid sunglasses, the glasses help to reduce the glare from sunlight reflecting off the water. But if you lie on your side on the beach, there
When a sheet of plastic food wrap is placed between two crossed polarizers, no light is transmitted. When the sheet is stretched in one direction, some light passes through the crossed polarizers.
It has been proposed that automobile windshields and headlights should have polarizing filters to reduce the glare of oncoming lights during night driving. Would this work? How should the polarizing
How can you determine the direction of the polarizing axis of a single polarizer?
Does it make sense to talk about the polarization of a longitudinal wave, such as a sound wave? Why or why not?
A salesperson at a bargain counter claims that a certain pair of sunglasses has Polaroid filters; you suspect that the glasses are just tinted plastic. How could you find out for sure?
When light is incident on an interface between two materials, the angle of the refracted ray depends on the wavelength, but the angle of the reflected ray does not. Why should this be?
A ray of light in air strikes a glass surface. Is there a range of angles for which total internal reflection occurs? Explain.
If you look up from underneath toward the surface of the water in your aquarium, you may see an upside-down reflection of your pet fish in the surface of the water. Explain how this can happen.
Sometimes when looking at a window, you see two reflected images slightly displaced from each other. What causes this?
When hot air rises from a radiator or heating duct, objects behind it appear to shimmer or waver. What causes this?
A student claimed that, because of atmospheric refraction (see Discussion Question Q33.2), the sun can be seen after it has set and that the day is therefore longer than it would be if the earth had
A beam of light goes from one material into another. On physical grounds, explain why the wavelength changes but the frequency and period do not.
Sunlight or starlight passing through the earth’s atmosphere is always bent toward the vertical. Why? Does this mean that a star is not really where it appears to be? Explain.
Light requires about 8 minutes to travel from the sun to the earth. Is it delayed appreciably by the earth’s atmosphere? Explain.
Doubling the frequency of a wave in the range of 25 Hz to 3 kHz represents what change in the maximum allowed electromagnetic-wave intensity?(a) A factor of 2;(b) A factor of 1/√2;(c) A factor of
In the United States, household electrical power is provided at a frequency of 60 Hz, so electromagnetic radiation at that frequency is of particular interest. On the basis of the ICNIRP guidelines,
As a physics lab instructor, you conduct an experiment on standing waves of microwaves, similar to the standing waves produced in a microwave oven. A transmitter emits microwaves of frequency f . The
Because the speed of light in vacuum (or air) has such a large value, it is very difficult to measure directly. To measure this speed, you conduct an experiment in which you measure the amplitude of
The energy flow to the earth from sunlight is about 1.4 kW/m2.(a) Find the maximum values of the electric and magnetic fields for a sinusoidal wave of this intensity.(b) The distance from the earth
Does an electromagnetic standing wave have energy? Does it have momentum? Are your answers to these questions the same as for a traveling wave? Why or why not?
A light source radiates a sinusoidal electromagnetic wave uniformly in all directions. This wave exerts an average pressure p on a perfectly reflecting surface a distance R away from it. What average
If a light beam carries momentum, should a person holding a flashlight feel a recoil analogous to the recoil of a rifle when it is fired? Why is this recoil not actually observed?
Most automobiles have vertical antennas for receiving radio broadcasts. Explain what this tells you about the direction of polarization of E̅(vector) in the radio waves used in broadcasting.
The magnetic-field amplitude of the electromagnetic wave from the laser described in Example 32.1 (Section 32.3) is about 100 times greater than the earth’s magnetic field. If you illuminate a
For a certain sinusoidal wave of intensity I, the amplitude of the magnetic field is B. What would be the amplitude (in terms of B) in a similar wave of twice the intensity?
The light beam from a searchlight may have an electricfield magnitude of 1000 V/m, corresponding to a potential difference of 1500 V between the head and feet of a 1.5-m-tall person on whom the light
Suppose that a positive point charge q is initially at rest on the x-axis, in the path of the electromagnetic plane wave described in Section 32.2. Will the charge move after the wave front reaches
Is polarization a property of all electromagnetic waves, or is it unique to visible light? Can sound waves be polarized? What fundamental distinction in wave properties is involved? Explain.
Medical x rays are taken with electromagnetic waves having a wavelength of around 0.10 nm in air. What are the frequency, period, and wave number of such waves?
Sometimes neon signs located near a powerful radio station are seen to glow faintly at night, even though they are not turned on. What is happening?
Give several examples of electromagnetic waves that are encountered in everyday life. How are they all alike? How do they differ?
When driving on the upper level of the Bay Bridge, westbound from Oakland to San Francisco, you can easily pick up a number of radio stations on your car radio. But when driving eastbound on the
By measuring the electric and magnetic fields at a point in space where there is an electromagnetic wave, can you determine the direction from which the wave came? Explain.
If the frequency at which the electrode is oscillated is increased to a very large value, the electrode’s impedance(a) Approaches infinity;(b) Approaches zero;(c) Approaches a constant but nonzero
The signal from the oscillating electrode is fed into an amplifier, which reports the measured voltage as an rms value, 1.5 nV. What is the potential difference between the two extremes?(a) 1.5
If the electrode oscillates between two points 20 mm apart at a frequency of (5000/π)Hz, what is the electrode’s impedance?(a) 0;(b) Infinite;(c) √2 × 104 Ω;(d) √2 × 106 Ω.An individual
What is the dc impedance of the electrode, assuming that it behaves as an ideal capacitor?(a) 0;(b) Infinite;(c) √2 × 104 Ω;(d) √2 × 106 Ω.An individual cell such as an egg cell (an ovum,
An ideal transformer has N1 windings in the primary and N2 windings in its secondary. If you double only the number of secondary windings, by what factor does(a) The voltage amplitude in the
Can a transformer be used with dc? Explain. What happens if a transformer designed for 120-V ac is connected to a 120-V dc line?
A circuit consists of a light bulb, a capacitor, and an inductor connected in series to an ac source. Is it possible for both the capacitor and the inductor to be removed and the brightness of the
A coil of wire wrapped on a hollow tube and a light bulb are connected in series to an ac source. What happens to the brightness of the bulb when an iron rod is inserted in the tube?
A light bulb and a parallel-plate capacitor with air between the plates are connected in series to an ac source. What happens to the brightness of the bulb when a dielectric is inserted between the
In Example 31.6 (Section 31.4), a hair dryer is treated as a pure resistor. But because there are coils in the heating element and in the motor that drives the blower fan, a hair dryer also has
When an L-R-C series circuit is connected across a 120-V ac line, the voltage rating of the capacitor may be exceeded even if it is rated at 200 or 400 V. How can this be?
In an L-R-C series circuit, what are the phase angle ϕ and power factor cos ϕ when the resistance is much smaller than the inductive or capacitive reactance and the circuit is operated far from
In an L-R-C series circuit, can the instantaneous voltage across the capacitor exceed the source voltage at that same instant? Can this be true for the instantaneous voltage across the inductor?
Is it possible for the power factor of an L-R-C series ac circuit to be zero? Justify your answer on physical grounds.
Equation (31.9) says that vab= L di/dt (see Fig. 31.8a). Using Faraday€™s law, explain why point a is at higher potential than point b when i is in the direction shown in Fig. 31.8a and is
Fluorescent lights often use an inductor, called a ballast, to limit the current through the tubes. Why is it better to use an inductor rather than a resistor for this purpose?
Equation (31.14) was derived by using the relationship i = dq/dt between the current and the charge on the capacitor. In Fig. 31.9a the positive counterclockwise current increases the charge on the
In an ac circuit, why is the average power for an inductor and a capacitor zero, but not for a resistor?
The current in an ac power line changes direction 120 times per second, and its average value is zero. Explain how it is possible for power to be transmitted in such a system.
Household electric power in most of western Europe is supplied at 240 V, rather than the 120 V that is standard in the United States and Canada. What are the advantages and disadvantages of each
If all of the magnetic energy stored in this MRI magnet is converted to thermal energy, how much liquid helium will boil off? (a) 27 kg; (b) 38 kg; (c) 60 kg; (d) 110 kg.
If part of the magnet develops resistance and liquid helium boils away, rendering more and more of the magnet nonsuperconducting, how will this quench affect the time for the current to drop to half
If a small part of this magnet loses its superconducting properties and the resistance of the magnet wire suddenly rises from 0 to a constant 0.005 Ω, how much time will it take for the current to
How many turns does this typical MRI magnet have?(a) 1100;(b) 3000;(c) 4000;(d) 22,000.Magnets carrying very large currents are used to produce the uniform, large-magnitude magnetic fields that are
Consider the circuit in Exercise 30.23.(a) Just after the circuit is completed, at what rate is the battery supplying electrical energy to the circuit?(b) When the current has reached its final
In an L-R-C series circuit, what criteria could be used to decide whether the system is overdamped or underdamped? For example, could we compare the maximum energy stored during one cycle to the
Suppose there is a steady current in an inductor. If you attempt to reduce the current to zero instantaneously by quickly opening a switch, an arc can appear at the switch contacts. Why? Is it
In the R-L circuit shown in Fig. 30.11, is the current in the resistor always the same as the current in the inductor? How do you know?Fig.30.11 Closing switch S, connects the R-L combination in
A toroidal solenoid has mean radius 12.0 cm and crosssectional area 0.600 cm2.(a) How many turns does the solenoid have if its inductance is 0.100 mH?(b) What is the resistance of the solenoid if the
In the R-L circuit shown in Fig. 30.11, when switch S1 is closed, the potential vac changes suddenly and discontinuously, but the current does not. Explain why the voltage can change suddenly
In Section 30.5 the relationship i = dq/dt is used in deriving Eq. (30.20). But a flow of current corresponds to a decrease in the charge on the capacitor. Explain, therefore, why this is the correct
In Section 30.5 Kirchhoff’s loop rule is applied to an L-C circuit where the capacitor is initially fully charged and the equation -L (di/dt) - (q/C) = 0 is derived. But as the capacitor starts to
In an R-C circuit, a resistor, an uncharged capacitor, a dc battery, and an open switch are in series. In an R-L circuit, a resistor, an inductor, a dc battery, and an open switch are in series.
For the same magnetic field strength B, is the energy density greater in vacuum or in a magnetic material? Explain. Does Eq. (30.11) imply that for a long solenoid in which the current is I the
You are to make a resistor by winding a wire around a cylindrical form. To make the inductance as small as possible, it is proposed that you wind half the wire in one direction and the other half in
Two closely wound circular coils have the same number of turns, but one has twice the radius of the other. How are the self-inductances of the two coils related? Explain your reasoning.
Two identical, closely wound, circular coils, each having self-inductance L, are placed next to each other, so that they are coaxial and almost touching. If they are connected in series, what is the
The tightly wound toroidal solenoid is one of the few configurations for which it is easy to calculate self-inductance. What features of the toroidal solenoid give it this simplicity?
In Fig. 30.1, if coil 2 is turned 90° so that its axis is vertical, does the mutual inductance increase or decrease? Explain.Fig.30.1 Coil 1 Nj turns Coil 2 N2 turns Фв2 it
In an electric trolley or bus system, the vehicle’s motor draws current from an overhead wire by means of a long arm with an attachment at the end that slides along the overhead wire. A brilliant
Which graph in Fig. P29.74 best represents the time t dependence of the current i induced in the brain tissue, assuming that this tissue can be modeled as a resistive circuit? (The units of i are
It may be desirable to increase the maximum induced current in the brain tissue. In Fig. P29.73, which time-dependent graph of the magnetic field B in the coil achieves that goal? Assume that
Consider the brain tissue at the level of the dashed line to be a series of concentric circles, each behaving independently of the others. Where will the induced emf be the greatest?(a) At the center
In part (a) of the figure, a current pulse increases to a peak and then decreases to zero in the direction shown in the stimulating coil. What will be the direction of the induced current (dashed
Blood contains positive and negative ions and thus is a conductor. A blood vessel, therefore, can be viewed as an electrical wire. We can even picture the flowing blood as a series of parallel
A 0.250-m-long bar moves on parallel rails that are connected through a 6.00-Î© resistor, as shown in Fig. E29.33, so the apparatus makes a complete circuit. You can ignore the resistance
Consider the circuit shown in Fig. E29.31, but with the bar moving to the right with speed v. As in Exercise 29.31, the bar has length 0.360 m, R = 45.0 Î©, and B = 0.650 T.(a) Is the
A rectangular loop of wire with dimensions 1.50 cm by 8.00 cm and resistance R = 0.600 Î© is being pulled to the right out of a region of uniform magnetic field. The magnetic field has

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