Q&A Hero

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: Materials generally become warmer when light is A) absorbed by them. B) reflected by them. C) transmitted by them. D) all of the above E) none of the above

Q: Metals are shiny because A) they reflect 100% of incident light. B) they are poor absorbers of light. C) their electrons vibrate to the oscillations of any incident light. D) none of the above

Q: Infrared waves are often called heat waves because they A) emanate from relatively hot sources. B) consist of frequencies lower than those of visible light. C) induce resonance in molecules and increase internal energy in a substance. D) are the predominant waves emitted by the sun.

Q: Glass is transparent to wave frequencies that A) match its natural frequencies. B) are below its natural frequencies. C) both of these D) neither of these

Q: Consider light energy that is momentarily absorbed in glass and then re-emitted. Compared to the absorbed light, the frequency of the re-emitted light is A) considerably less. B) slightly less. C) the same. D) slightly more. E) considerably more.

Q: When ultraviolet light is incident upon glass, atoms in the glass A) are forced into vibration. B) resonate. C) pass the light energy along practically undiminished. D) freely absorb and re-emit most of the ultraviolet light.

Q: Glass is transparent to A) infrared light. B) visible light. C) ultraviolet light. D) all of the above

Q: Compared to the photon that enters a pane of window glass, the photon that emerges is A) the same photon. B) an identical but different photon. C) an altogether different photon. D) none of the above

Q: Compared to its average speed in air, the average speed of a beam of light in glass is A) more. B) less. C) the same.

Q: The speed of light in the void between molecules in glass is A) more than its speed in a vacuum. B) the same as its speed in a vacuum. C) less than its speed in a vacuum.

Q: When visible light is incident upon clear glass, atoms in the glass A) are forced into vibration. B) resonate. C) convert the light energy into internal energy.

Q: The natural frequency of the atoms in glass is in the A) infrared part of the spectrum. B) visible part of the spectrum. C) ultraviolet part of the spectrum.

Q: If an electron vibrates up and down 1000 times each second, it generates an electromagnetic wave having a A) period of 1000 s. B) speed of 1000 m/s. C) wavelength of 1000 m. D) frequency of 1000 Hz. E) wavelength of 1000 km.

Q: If an electric charge is shaken up and down frequently enough A) sound can be emitted. B) light can be emitted. C) both of these D) neither of these

Q: Which of the following cannot travel in a vacuum? A) a light wave B) a sound wave C) a radio wave D) all can E) none can

Q: The fact that you can see stars in the nighttime sky is evidence that A) our atmosphere is transparent to visible light. B) light can travel in a vacuum. C) both of these D) neither of these

Q: Kids in elementary school get this right: Which color of light gets through red glass? A) red B) cyan C) none of these

Q: Which best shields you from sunburn when at the beach? A) a cloudy day B) a sheet of glass between you and the Sun C) frequent turning of your body D) all of the above E) none of the above

Q: Sunburns are produced by A) infrared light. B) visible light. C) ultraviolet light. D) all of the above E) none of the above

Q: A main difference between a radio wave and a sound wave is A) frequency. B) wavelength. C) energy. D) amplitude. E) medium or no medium.

Q: What is the frequency of an electromagnetic wave that has a wavelength of 300,000 km? A) less than 1 Hz B) 1 Hz C) more than 1 Hz

Q: What is the wavelength of an electromagnetic wave that has a frequency of 3 kilohertz? A) less than 1 km B) 1 km C) more than 1 km

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: Thrust a magnet into the opening of a rubber band and it A) rotates. B) then has a current in it. C) both of these D) neither of these

Q: If you thrust a magnet into a closed loop of wire, the loop will A) rotate. B) have a current in it. C) both of these D) neither of these

Q: When a change occurs in the magnetic field in a closed loop of wire A) a voltage is induced in the wire. B) a current is created in the loop of wire. C) electromagnetic induction occurs. D) all of the above E) none of the above

Q: Electromagnetic induction is employed in A) electric power lines. B) triggering traffic lights. C) hybrid automobiles. D) mobile phones. E) all the above

Q: The discovery of electromagnetic induction is credited to A) Joseph Henry in America. B) Michael Faraday in England. C) both of these D) neither of these

Q: Electromagnetism unites A) electricity and magnetism. B) electric and gravitational fields. C) physics and biophysics. D) all of the above E) none of the above

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