Q&A Hero

Q: What is the wavelength of a 1-hertz electromagnetic wave? A) less than 1 m B) 1 m C) more than 1 m

Q: If the color spectrum ranges from red to violet, then it ranges from A) low frequencies to high frequencies. B) long wavelengths to short wavelengths. C) both of these D) neither of these

Q: A main difference between a radio wave and a light wave is A) wavelength. B) frequency. C) both of these D) neither of these

Q: Compared to radio waves, the velocity of visible light waves in a vacuum is A) less. B) more. C) the same.

Q: Compared to ultraviolet waves, the frequency of infrared waves is A) lower. B) the same. C) higher.

Q: Compared to ultraviolet waves, the wavelength of infrared waves is A) shorter. B) the same. C) longer.

Q: Which of these electromagnetic waves have the longest wavelength? A) radio waves B) infrared waves C) X-rays D) ultraviolet waves E) light waves

Q: Which of these electromagnetic waves have the shortest wavelength? A) radio waves B) infrared waves C) X-rays D) ultraviolet waves E) light waves

Q: Which travels with the greatest speed in a vacuum? A) radio waves B) light waves C) X-rays D) gamma rays E) all have the same speed

Q: Which of the following is fundamentally different from the others? A) sound waves B) X-rays C) gamma rays D) light waves E) radio waves

Q: If the Sun were to disappear at this moment, we wouldn't know about it for A) 7 seconds, reflex time. B) 8 seconds. C) 8 minutes. D) 8 hours.

Q: If a light signal and a radio signal were emitted simultaneously from Alpha Centauri, the first to reach Earth would be the A) radio signal. B) light signal. C) both the same time

Q: The fact that light travels only at 300,000 km/s in free space is a consequence of A) electromagnetic wave propagation. B) electromagnetic field induction. C) Maxwell's laws. D) energy conservation. E) none of the above

Q: Radio waves travel A) always much faster than sound waves. B) in common cases at the same speed as sound waves. C) slower, on average, than sound waves. D) at a speed that depends on frequency.

Q: Your friend says that any radio wave travels appreciably faster than any sound wave. A) agree with your friend unconditionally B) agree with your friend for most common cases C) disagree with your friend D) find a new friend

Q: In free space, electromagnetic waves travel at a A) variety of speeds. B) single speed. C) speed depending on frequency.

Q: A changing electric field induces a changing A) magnetic field. B) electromagnetic field. C) both of these D) neither of these

Q: The source of all electromagnetic waves is A) changes in atomic energy levels. B) vibrating atoms and molecules. C) accelerating electric charges. D) crystalline fluctuations. E) none of the above

Q: Electromagnetic waves consist of A) compressions and rarefactions of electromagnetic pulses. B) oscillating electric and magnetic fields. C) particles of light energy. D) high-frequency sound waves.

Q: Most of the waves in the electromagnetic spectrum are A) red light. B) blue light. C) green light. D) invisible.

Q: Colors are barely seen or not at all in nighttime because moonlight A) has almost no colors in it. B) is too dim to activate the retina's cones. C) photons don't have enough energy to activate the retina's cones. D) is primarily yellow light. E) is only semi-transparent in Earth's atmosphere.

Q: The main difference between the retina of a human eye and that of a dog's eye is the A) predominance of cones in a dog's retina. B) absence of cones in a dog's retina. C) more intricate optic nerve in a human's eye. D) small number of cones in a human's eye. E) none of the above

Q: Our eyes are not very good at seeing A) motion at our peripheries. B) differences in brightness. C) color in dim light. D) all of the above E) none of the above

Q: The size of the pupil of your eye depends on A) the brightness of light in the room. B) your mood. C) both of these D) neither of these

Q: Information-carrying nerves are connected to the retina at the A) fovea. B) blind spot. C) cornea. D) iris. E) periphery.

Q: In the periphery of our vision, we are A) more sensitive to low frequencies than high ones. B) insensitive to color and movement. C) sensitive to movement, but cannot see color. D) sensitive to both movement and color. E) none of the above

Q: Red-hot and blue-hot stars appear white to the eye because A) the eye has difficulty seeing color at night. B) they are too dim to fire the cones. C) they are too dim to fire the rods. D) they are overwhelmed by the blackness of the nighttime sky. E) eye receptivity peaks in the yellow-green part of the spectrum.

Q: The cones in the retina of the eye are A) most densely packed at the center of vision. B) uniformly spread along the visual field. C) concentrated along the periphery of vision.

Q: The sensation of color is seen when light falls on the eye's A) rods. B) cones. C) both of these D) neither of these

Q: When an astronaut on the Moon experiences a solar eclipse, observers on Earth see A) a lunar eclipse. B) a solar eclipse. C) no eclipse at all.

Q: A new Moon appears in the sky just before the time of a A) solar eclipse. B) lunar eclipse. C) both of these D) neither of these

Q: The Moon would be at its fullest just before the time of a A) solar eclipse. B) lunar eclipse. C) both of these D) neither of these

Q: The crescent shapes of spots of light cast through openings in trees occurs with a A) partial eclipse of the Sun. B) total eclipse of the Sun. C) lunar eclipse, partial or total. D) partial lunar eclipse.

Q: The round spots of light on the ground beneath a tree on a sunny day are images of A) the openings between leaves above. B) nothing in particular. C) the Sun.

Q: An annular eclipse of the Sun occurs when the Moon doesn't quite cover the Sun in the zone of totality. This means that the Moon is A) closer than usual to Earth. B) farther than usual from Earth. C) none of these

Q: While Earth is experiencing a total solar eclipse, an observer on the side of the Moon facing Earth would see A) Earth disappear from the sky. B) Earth dim and turn reddish. C) nothing unusual. D) a dark area moving across the face of Earth.

Q: A partial solar eclipse occurs for people in the Sun's A) umbra. B) penumbra. C) none of these

Q: A total solar eclipse occurs for people in the Sun's A) umbra. B) penumbra. C) none of these

Q: A solar eclipse occurs when the A) Sun passes into Earth's shadow. B) Moon passes into Earth's shadow. C) the Moon's shadow is cast on Earth. D) none of the above

Q: A lunar eclipse occurs when the A) Sun passes into Earth's shadow. B) Moon passes into Earth's shadow. C) Earth passes into the Sun's shadow. D) Earth passes into the Moon's shadow.

Q: A total shadow is called A) an umbra, and a partial shadow a penumbra. B) a penumbra, and a partial shadow an umbra. C) neither of these

Q: A pair of sunglasses and a pair of clear reading glasses are left in the sunlight. The hotter glasses will be the A) sunglasses. B) reading glasses. C) both of these D) neither of these

Q: Earth's atmosphere is opaque to waves that are concentrated in the A) infrared part of the spectrum. B) visible part of the spectrum. C) entire electromagnetic spectrum.

Q: A friend says that changing electric and magnetic fields underlie the production of light. A) agree with your friend B) argue to the contrary with your friend. C) find a new friend.

Q: Induced electric and magnetic fields result in A) electromagnetic waves. B) stronger electric or magnetic fields. C) higher voltages produced by Faraday induction. D) all of the above E) none of the above

Q: The induced electric and magnetic fields of Maxwell are A) parallel to each other. B) perpendicular to each other. C) non-directional.

Q: In the field induction credited to Maxwell, wires A) can be insulated or non-insulated. B) are minimized. C) are not needed.

Q: The strength of an induced electric or magnetic field depends on A) strength of magnetic poles. B) alignment of magnetic domains. C) rate of change of the induced field. D) all of the above E) none of the above

Q: A force field is induced in any region of space in which A) an electric field changes with time. B) a magnetic field changes with time. C) both of these D) neither of these

Q: Rapid change of a magnetic field induces A) a magnetic field of greater magnitude. B) a magnetic field of the same magnitude. C) an electric field.

Q: Faraday's law was extended by Maxwell toward A) changes in electric fields. B) changes in magnetic fields. C) both of these D) neither of these

Q: When voltage is stepped up in a transformer, current is stepped down. But Ohm's law tells us that greater voltage means greater current, not less current. How then can current be lower when voltage is increased? A) Current in the secondary is lower when compared to the greater current drawn by the primary. B) Ohm's law applies to the circuit connected to the secondary, not to the transformer. C) both of these D) neither of these

Q: High-voltage wires in power lines are not high-current wires because the current in them is A) not the same as the current that powers the distant load. B) proportional to the voltage drop from beginning to end of each line, rather low. C) both of these D) neither of these

Q: The high voltage that is important in a power line is high voltage A) between the parallel wires of the line. B) from one end of each power line to the other. C) both of these D) neither of these

Q: The spacing between the parallel power lines is affected by A) current-carrying capacities of wires. B) electrical insulation. C) the wing span of birds in the vicinity. D) none of the above

Q: Power is transmitted at high voltages because the corresponding current in the wires is A) also high to deliver appreciable power to distant places. B) low so that overheating of the wires is minimized. C) either of these D) neither of these

Q: Between the consumer and the power plant, most importantly, are A) huge capacitors. B) generators. C) step-down transformers. D) all of the above E) none of the above

Q: The principal advantage of ac power over dc power is that A) more energy is dissipated during transmission. B) ac voltage oscillates while dc voltage does not. C) ac voltage can be transformed via conventional transformers. D) ac circuits multiply power more easily. E) ac circuits are safer.

Q: The transmission of power from one place to another is evident in A) household electricity. B) radio broadcast. C) mobile phones. D) all of the above

Q: Underlying the concept of self-induction is A) Ohm's law. B) Faraday's law. C) Maxwell's law. D) all of these about equally

Q: To reduce the danger of self-induction A) simply pull the circuit plug. B) turn off the switch to the circuit. C) either of these D) neither of these

Q: The voltage induced in self-inductions is A) always in a direction opposing the changing voltage that produced it. B) likely higher than the changing voltage that causes it. C) both of these D) neither of these

Q: Disconnect a small-voltage battery from a coil of many loops of wire and a large voltage may be produced by A) the sudden collapse in the magnetic field. B) latent energy in the battery. C) the resistance of the battery to a change in polarity. D) electrons already in the wire. E) the electric field between the battery terminals.

Q: If the primary of a transformer is connected to a dc power source, the transformer would have a voltage output A) at a higher efficiency than with an ac source. B) the same. C) that is also dc. D) only while being connected or disconnected. E) none of the above

Q: Four amperes of current exist in the primary coil of a transformer. The voltage across the primary coil is 120 V. What is the power output of the secondary coil? A) 30 W B) 120 W C) 480 W D) 960 W E) need more information

Q: The voltage across the input terminals of a transformer is 120 V. The primary has 25 loops and the secondary has 50 loops. The voltage the transformer delivers is A) 30 V. B) 60 V. C) 120 V. D) 240 V. E) none of the above

Q: The voltage across the input terminals of a transformer is 120 V. The primary has 50 loops and the secondary has 25 loops. The voltage the transformer delivers is A) 30 V. B) 60 V. C) 120 V. D) 240 V. E) none of the above

Q: Neon signs require about 12,000 volts to operate. If the circuit uses a 120-volt power source, the ratio of primary to secondary turns on the transformer should be A) 1 primary to 100 secondary. B) 100 primary to 1 secondary. C) neither of these

Q: A certain transformer doubles input voltage. If the primary coil draws 10 A of current, then the current in the secondary coil is A) 2 A. B) 5 A. C) 10 A. D) 25 A. E) none of the above

Q: A step-up transformer steps up voltage by ten times. Neglecting slight losses, if 100 W of power go into the primary coil, the power coming from the secondary coil is A) 1 W. B) 10 W. C) 100 W. D) 1000 W. E) none of the above

Q: A step-up transformer steps up voltage by ten times. If voltage input is 120 volts, voltage output is A) 60 V. B) 120 V. C) 1200 V. D) 12000 V. E) none of the above

Q: An iron core in a transformer A) guides magnetic field lines. B) shields unwanted external electric or magnetic fields. C) separates the primary and secondary regions. D) reduces energy losses.

Q: The primary of a transformer A) has an iron core. B) may or may not have an iron core. C) has more turns of wire than the secondary. D) none of the above

Q: The secondary of a transformer is the coil connected to A) the load. B) the Internet. C) the input power line. D) none of the above

Q: The primary of a transformer is the coil connected to A) the load. B) the Internet. C) the input power line. D) none of the above

Q: A transformer produces A) energy. B) power. C) neither, but transforms mechanical energy to electric energy. D) none of the above

Q: An efficient step-down transformer decreases A) power. B) energy. C) both of these D) neither of these

Q: An efficient step-up transformer boosts A) energy. B) power. C) voltage. D) all of the above E) none of the above

Q: The principle difference between a step-up and step-down transformer is A) step-up transformers can handle more current. B) different geometries. C) different ratios of turns of wire for each. D) none of the above

Q: Compared to the primary voltage, the secondary voltage can be A) higher. B) lower. C) the same. D) any of the above E) none of the above