Questions and Answers of Essential University Physics

You’re an optometrist helping a nearsighted patient who claims he can’t see clearly beyond 80 cm. Prescribe a lens that will put the images of distant objects at 80 cm, giving your patient clear
What focal length should you specify if you want a magnifying glass with angular magnification 3.2?
You have to hold a book 55 cm from your eyes for the print to be in focus. What power lens would correct your farsightedness?
You?re underwater, looking through a spherical air bubble (Fig. 31.35). What?s its actual diameter if it appears, along your line of sight, to be 1.5cm in diameter? 1.5 cm FIGURE 31.35 Exercise 32
A tiny insect is trapped 1.0 mm from the center of a spherical dewdrop 4.0mm in diameter. As you look straight into the drop, what’s the insect’s apparent distance from the drop’s surface?
The bottom of a swimming pool looks to be 1.5m below the surface. Find the pool’s actual depth.
You’re standing in a wading pool and your feet appear to be 30cm below the surface. How deep is the pool?
You’re writing specifications for a new line of magnifying glasses that have double-convex lenses with equal 32-cm curvature radii, made from glass with n = 1.52. What do you list for the focal
A magnifying glass enlarges print by 50% when it’s 9.0 cm from a page. What’s its focal length?
A real image is four times as far from a lens as is the object. What’s the object distance, measured in focal lengths?
By holding a magnifying glass 25 cm from your desk lamp, you can focus an image of the lamp’s bulb on a wall 1.6 m from the lamp. What’s the focal length of your magnifying glass?
A lens with 50-cm focal length produces a real image the same size as the object. How far from the lens are image and object?
By what factor is the image magnified for an object 1.5 focal lengths from a converging lens? Is the image upright or inverted?
A lightbulb is 56 cm from a convex lens. Its image appears on a screen 31 cm from the lens, on the other side. (a) the lens’s focal length(b) how much the image is enlarged or reduced.
(a) Where on the axis of a concave mirror would you place an object to get a half-size image?(b) Where will the image be located?(c) Will the image be real or virtual?
A virtual image is located 40 cm behind a concave mirror with focal length 18 cm.(a) Where is the object?(b) By how much is the image magnified?
An object is five focal lengths from a concave mirror.(a) How do the object and image heights compare?(b) Is the image upright or inverted?
A candle is on the axis of a 15-cm-focal-length concave mirror, 36 cm from the mirror.(a) Where is its image?(b) How do the image and object sizes compare?(c) Is the image real or virtual?
A shoe store uses small floor-level mirrors to let customers view prospective purchases. At what angle should such a mirror be inclined so that a person standing 50cm from the mirror with eyes 140cm
Mirages occur when air?s refractive index varies with position as a result of uneven heating. Under such conditions, light undergoes refraction continually and thus follows a curved path. Other
Mirages occur when air?s refractive index varies with position as a result of uneven heating. Under such conditions, light undergoes refraction continually and thus follows a curved path. Other
Mirages occur when air?s refractive index varies with position as a result of uneven heating. Under such conditions, light undergoes refraction continually and thus follows a curved path. Other
Mirages occur when air?s refractive index varies with position as a result of uneven heating. Under such conditions, light undergoes refraction continually and thus follows a curved path. Other
Proposals have been made to ?sail? spacecraft to the outer solar system using the pressure of sunlight, or even to propel interstellar spacecraft with high-powered, Earth-based lasers. Sailing
Proposals have been made to ?sail? spacecraft to the outer solar system using the pressure of sunlight, or even to propel interstellar spacecraft with high-powered, Earth-based lasers. Sailing
Proposals have been made to ?sail? spacecraft to the outer solar system using the pressure of sunlight, or even to propel interstellar spacecraft with high-powered, Earth-based lasers. Sailing
Proposals have been made to ?sail? spacecraft to the outer solar system using the pressure of sunlight, or even to propel interstellar spacecraft with high-powered, Earth-based lasers. Sailing
The National Ignition Facility at Lawrence Livermore National Laboratory initiates nuclear fusion by converging 192 laser beams on a deuterium tritium target. Each beam has a square cross section 38
Your friend who works for the college radio station must make electric-field measurements for a report to be filed with the station’s application for license renewal. The measurement is made 4.6km
The Voyager 1 spacecraft is now beyond the outer reaches of our solar system, but earthbound scientists still receive data from the spacecraft’s 20-W radio transmitter. Voyager is expected to
Your roommate’s father is CEO of a coal company, so your roommate is understandably skeptical of alternative energy proposals. He claims that there’s no future for solar energy, because the power
A friend buys a used pickup truck that comes with a CB radio. However, the antenna is broken off, and your friend asks you to help make one out of a steel rod that he will affix to the rear bumper.
Maxwell’s equations in a dielectric resemble those in vacuum (Equations 29.6–29.9) but with ε0 replaced by kε0, where k is the dielectric constant introduced in Chapter 23. Show that the speed
You’re an astronomer studying the origin of the solar system, and you’re evaluating a hypothesis that sufficiently small particles were blown out of the solar system by the force of sunlight. To
In a stack of polarizing sheets, each sheet has its transmission axis rotated 14° with respect to the preceding sheet. If the stack passes 37% of the incident unpolarized light, how many sheets does
A cylindrical resistor of length L, radius a, and resistance R carries current I. Calculate the electric and magnetic fields at the surface of the resistor, assuming the electric field is uniform
A radar system produces pulses consisting of exactly 100 full cycles of a sinusoidal 72.5-GHz electromagnetic wave. The average power while the transmitter is on is 66.0 MW, and the waves are
A white dwarf star is approximately the size of Earth but radiates about as much power as the Sun. Estimate the radiation pressure on a light-absorbing object at the white dwarf’s surface.
A photon rocket emits a beam of light instead of hot gas. How powerful a beam would be needed to equal the 40-MN thrust of NASA’s new Space Launch System (SLS)? Compare your answer with
A 65-kg astronaut is floating in empty space. If she shines a 1.0-W flashlight in a fixed direction, how long will it take her to accelerate to 10m/s?
A 180W/cm2 laser beam shines on a light-absorbing surface. What’s the radiation pressure on the surface?
A laser produces an average power of 7.0W in a 1.0-mm-diameter beam. Find(a) the average intensity (b) the peak electric field of the laser light.
A camera flash delivers 2.5 kW of light power for 1.0ms. Find(a) the total energy(b) the total momentum carried by the flash.
A typical fluorescent lamp is a little more than 1 m long and a few cm in diameter. How do you expect the light intensity to vary with distance(a) near the lamp but not near either end and(b) far
Find the peak electric and magnetic fields 1.5m from a 60-W lightbulb that radiates equally in all directions.
At 1.5 km from a radio transmitter, the peak electric field is 350 mV/m. Assuming the transmitter broadcasts equally in all directions, find(a) the transmitted power(b) the peak electric field 10 km
Lasers are classified according to the eye-damage danger they pose. Class 2 lasers, including many laser pointers, produce visible light with no greater than 1 mW total power. They’re relatively
A quasar 10 billion light-years from Earth appears the same brightness as a star 50,000 light-years away. How do the power outputs of quasar and star compare?
Use the fact that sunlight intensity at Earth’s orbit is 1364 W/m2 to calculate the Sun’s total power output.
High microwave intensities can cause biological damage through heating of tissue; a particular concern is cataract formation. The U.S. Food and Drug Administration limits microwave radiation near the
Show that it’s impossible for an electromagnetic wave in vacuum to have a time-varying component of its electric field in the direction of its magnetic field.
Vertically polarized light passes through two polarizers, the first at 60° to the vertical and the second at 90° to the vertical. What fraction of the light gets through?
Unpolarized light of intensity S0 passes first through a polarizer with its axis vertical and then through one with its axis at 35° to the vertical. Find the intensity after the second polarizer.
An electro-optic modulator is a device that switches a laser beam rapidly from off to on by switching the polarization direction through 90° when a voltage is applied. But a brownout results in only
A polarizer blocks 75% of a polarized light beam. What’s the angle between the beam’s polarization and the polarizer’s axis?
A radio receiver can detect signals with electric fields as weak as 320μV/m. Find the corresponding magnetic field.
Dielectric breakdown in air occurs when the electric field is approximately 3 MV/m. What would be the peak magnetic field in an electromagnetic wave with this peak electric field?
The medical profession divides the ultraviolet region of the electromagnetic spectrum into three bands: UVA (320 nm–420 nm), UVB (290 nm–320 nm), and UVC (100 nm–290 nm). UVA and UVB promote
An electric field points into the page and occupies a circular region of radius 1.0 m, as shown in Fig. 29.14. There are no electric charges in the region, but there is a magnetic field forming
You’re engineering a new cell phone, and you’d like to incorporate the antenna entirely within the phone, which is 9 cm long when closed. The antenna is to be a quarter-wavelength long a common
A parallel-plate capacitor has circular plates with radius 50.0 cm and spacing 1.0mm. A uniform electric field between the plates is changing at the rate of 1.0 MV/ms. Find the magnetic field between
Your university radio station has a 5.0-kW radio transmitter that broadcasts uniformly in all directions; listeners within 15 km have reliable reception. You want to increase the power to double that
A laser pointer delivers 0.10-mW average power in a beam 0.90mm in diameter. Find(a) the average intensity,(b) the peak electric field, (c) the peak magnetic field.
Your new radio says it can pick up signals with peak electric fields as weak as 450μV/m. Will it work if you take it to your remote cabin, where the intensity of your favorite radio station is 0.35
Estimate the peak electric field inside a 1.1-kW microwave oven under the simplifying approximation that the microwaves propagate as a plane wave through the oven’s 750cm2 cross-sectional area.
What would be the average intensity of a laser beam so strong that its electric field produced dielectric breakdown of air (which requires Ep = 3 MV/m)?
A typical laboratory electric field is 1500 V/m. Find the average intensity of an electromagnetic wave with this value for its peak field.
Vertically polarized light passes through a polarizer with its axis at 70° to the vertical. What fraction of the incident intensity emerges from the polarizer?
Polarized light is incident on a sheet of polarizing material, and only 20% of the light gets through. Find the angle between the electric field and the material’s transmission axis.
An electromagnetic wave is propagating in the z-direction. What’s its polarization direction if its magnetic field is in the y-direction?
An electromagnetic wave is propagating in the z-direction. What’s its polarization direction if its magnetic field is in the y-direction?
Microwave ovens for consumers’ use operate at 2.45 GHz. What’s the distance between wave crests in such a microwave?
A 60-Hz power line emits electromagnetic radiation. What’s the wavelength?
What are the wavelengths of(a) a 100-MHz FM radio wave,(b) a 5.0-GHz WiFi signal,(c) a 600-THz light wave,(d) a 1.0-EHz X ray?
If you speak via radio from Earth to an astronaut on the Moon, how long is it before you can receive a reply?
Your intercontinental telephone call is carried by electromagnetic waves routed via a satellite in geostationary orbit at 36,000 km altitude. Approximately how long does it take before your voice is
A light-minute is the distance light travels in 1 minute. Show that the Sun is about 8 light-minutes from Earth.
A radio wave’s electric field is given by the expression E(vector)) = E sin (kz – ωt) x (î + ĵ).(a) Find the peak electric field.(b) Give a unit vector in the direction of the magnetic field
The fields of an electromagnetic wave are E(vector) = Ep sin(kz + ωt)ĵ and B(vector) = Bp sin(kz + ωt)î. Give a unit vector in the wave’s propagation direction.
A parallel-plate capacitor has square plates 10 cm on a side and 0.50 cm apart. The voltage across the plates is increasing at 220V/ms. What’s the displacement current in the capacitor?
A uniform electric field is increasing at 1.5 (V/m)/μs. Find the displacement current through a 1 cm2 area perpendicular to the field.
A filter is a circuit designed to pass AC signals in some frequency range and to attenuate others. Common filters include low-pass filters, which allow low-frequency signals to pass but attenuate
A filter is a circuit designed to pass AC signals in some frequency range and to attenuate others. Common filters include low-pass filters, which allow low-frequency signals to pass but attenuate
A filter is a circuit designed to pass AC signals in some frequency range and to attenuate others. Common filters include low-pass filters, which allow low-frequency signals to pass but attenuate
A filter is a circuit designed to pass AC signals in some frequency range and to attenuate others. Common filters include low-pass filters, which allow low-frequency signals to pass but attenuate
Your professor tells you about the days before digital computers when engineers used electric circuits to model mechanical systems. Suppose a 5.0-kg mass is connected to a spring with k = 1.44 kN/m.
Substitute the expression for q1t2 in Equation 28.11 into the differential equation for an LC circuit with resistance, and find an expression for the angular frequency of the damped oscillations in
A triangle wave swings linearly between voltages -Vp and +Vp. Show that the rms voltage of a triangle wave is Vp √3.
For RLC circuits in which the resistance isn’t too high, the Q factor may be defined as the ratio of the resonant frequency to the difference between the two frequencies where the power dissipated
A sine-wave generator with 20-V peak output is applied across a series RLC circuit. At the resonant frequency of 2.0 kHz, the peak current is 50 mA; at 1.0 kHz, it’s 15 mA. Find R, L, and C.
A series RLC circuit with R = 47 Ω, L = 250mH, and C = 4.0 μF is connected across a sine-wave generator whose peak output voltage is independent of frequency. Find the frequency range over which
A “black box” has two input connections and two output connections. With a 12-V rms, 60-Hz sine wave across the inputs, the output is a 6.0-V, 60-Hz sine wave leading the input voltage by 45°.
Two capacitors are connected in parallel across a 24-V rms, 7.5-kHz sine-wave generator, and the generator supplies a total rms current of 56mA. With capacitors rewired in series, the rms current
Differentiate Equation 28.9 to find the current in the LC circuit, and use q = CV to find the voltage. From these, obtain the electric energy in the capacitor and the magnetic energy in the inductor,
A series RLC circuit with R = 1.3 Ω, L = 27 mH, and C = 0.33μF is connected across a sine-wave generator. If the capacitor’s peak voltage rating is 600 V, what’s the maximum safe value for the
An RLC circuit includes a 3.3μF capacitor and a 27-mH inductor. The capacitor is charged to 35V, and the circuit begins oscillating. Ten full cycles later the capacitor voltage peaks at 28V. Find
A power supply like that of Fig. 28.23 is supposed to deliver 22-V DC at a maximum current of 150 mA. The transformer?s peak output voltage can charge the capacitor to a full 22 V, and the primary is
A car-battery charger runs off the 120-V rms AC power line and supplies 10-A DC at 14V.(a) If the charger is 80% efficient in converting the line power to the DC power it supplies to the battery, how
You’re Chief Financial Officer for a power company, and you consult your engineering department in an effort to minimize powerline losses. Your power plant produces 60-Hz power at 365 kV rms and
A series RLC circuit has power factor 0.764 and impedance 182 Ω at 442 Hz. (a) What’s the resistance? (b) If the inductance is 25.0 mH, what’s the resonant frequency?

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