Q&A Hero

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

Q: Transformers use ac to satisfy the required A) transfer of energy from coil to coil. B) voltage for transformation. C) change in magnetic field for operation. D) change in input current. E) magnetic field intensities.

Q: The output power of an ideal transformer is A) greater than the input power. B) equal to the input power. C) smaller than the input power. D) may be any of the above

Q: A transformer transforms voltage while A) producing energy. B) producing power. C) transferring energy from one coil to another. D) transferring current from one coil to another.

Q: A transformer actually transforms A) voltage. B) magnetic field lines. C) generators into motors. D) non-safe forms of energy to safe forms of energy. E) all of the above

Q: The major advantage of MHD generators over conventional generators is that MHD generators A) do not use electromagnetic induction. B) do not require magnets. C) require no power input. D) all of the above E) none of the above

Q: A principle difference between an MHD generator and a conventional generator is that the MHD generator A) has no moving parts. B) operates more efficiently at high temperatures. C) both of these D) neither of these

Q: The rate at which energy is transferred is A) power. B) electromagnetic induction. C) transformation. D) none of the above

Q: A generator armature is more difficult to rotate when supplying electric current due to A) an induced magnetic field in the windings that resists change. B) increased resistance. C) energy leaking as heat. D) none of the above

Q: If the voltage produced by a generator alternates, it does so because A) unlike a battery, it produces alternating current. B) the changing magnetic field that produces it alternates. C) of alterations in the mechanical energy input. D) all of the above E) none of the above

Q: An electric motor is very similar to A) an electric generator. B) an automobile battery. C) a radio receiver. D) none of the above

Q: A turbogenerator produces A) energy. B) power. C) neither, but transforms energy from one form to another. D) none of the above

Q: The current produced by a common generator is A) dc. B) ac. C) neither of these

Q: A device that transforms mechanical energy into electrical energy is a A) generator. B) motor. C) transformer. D) magnet. E) none of the above

Q: A device that transforms electrical energy to mechanical energy is a A) generator. B) motor. C) transformer. D) magnet. E) none of the above

Q: If you drop a bar magnet in a vertical copper pipe it will fall slowly because A) of air resistance. B) it induces a magnetic field in the pipe that resists motion of the magnet. C) the copper is a good conductor of both electricity and magnetism. D) of electron repulsion.

Q: Fred swings a sheet of copper in pendulum fashion between the poles of a strong magnet. The sheet slows in entering the magnetic field because it A) induces swirling currents in the copper and accompanying magnetic fields that resist motion. B) experiences both air and magnetic friction. C) is repelled by free electrons in the copper. D) none of the above

Q: Disregarding the effects of friction, a cyclist will coast farther when a lamp powered by a wheel generator is A) of low wattage. B) of high wattage. C) turned off. D) none of the above

Q: The metal detectors that people walk through at airports operate via A) Ohm's law. B) Faraday's law. C) Coulomb's law. D) Newton's laws. E) civil laws.

Q: The amount of current produced by electromagnetic induction depends on the A) amount of induced voltage. B) resistance of the circuit to which it is connected. C) both of these D) neither of these

Q: The frequency of induced voltage in a wire coil depends on A) the frequency of current producing it. B) how frequently a magnet dips in and out of the coil. C) the number of loops in the coil.

Q: When a magnet is moved to and fro in a wire coil, voltage is induced. If the coil has twice as many loops, the voltage induced is A) half. B) the same. C) twice. D) four times as much. E) none of the above

Q: Faraday's law underlies the operation of A) an electric guitar. B) a shake flashlight. C) the changing of traffic lights. D) all of the above E) none of the above

Q: Magnetic field strength inside a current-carrying coil will be greater if the coil encloses a A) vacuum. B) wooden rod. C) glass rod. D) rod of iron. E) none of the above

Q: Voltage can be induced in a wire by A) moving the wire near a magnet. B) moving a magnet near the wire. C) changing the current in a nearby wire. D) all of the above E) none of the above

Q: Electromagnetic induction occurs in a coil when there is a change in A) electric field intensity in the coil. B) magnetic field intensity in the coil. C) electromagnetic polarity. D) none of the above

Q: When a bar magnet is thrust into a coil of copper wire, the coil tends to A) attract the magnet as it enters. B) repel the magnet as it enters. C) both of these D) neither of these

Q: When voltage is induced in a coil of wire, current is A) also induced. B) not induced. C) cancelled.

Q: Biomagnetism has been detected in A) bacteria. B) pigeons. C) wasps. D) humans. E) all of the above

Q: Pigeons navigate primarily by A) a good memory. B) a keen sense of smell. C) magnetic sensors in their heads. D) ultra-high-pitched sounds. E) none of the above

Q: Earth's magnetic field is A) something we've learned to live with. B) useful to pigeons but not to humans. C) protective to life on Earth.

Q: Cosmic rays penetrate your body when A) safely in your home. B) outdoors. C) in mountainous regions. D) all of the above E) none of the above

Q: An aurora borealis high above the atmosphere is due to A) disturbances in Earth's magnetic field. B) fountains of high-speed charged particles. C) trapping of charged particles by Earth's magnetic field. D) all of the above

Q: The intensity of cosmic rays bombarding the Earth's surface is most at the A) poles. B) mid-latitudes. C) equator.

Q: If a compass is moved from the Northern Hemisphere to the Southern Hemisphere, its magnetic needle will change direction A) randomly and rapidly B) by 90 degrees. C) by 180 degrees. D) hardly at all.

Q: Solar winds headed in Earth's direction are deviated mainly by A) the upper atmosphere. B) the troposphere. C) Earth's magnetic field. D) Earth's radiation belts.

Q: Over geologic history the Earth's magnetic field A) has been relatively stable. B) has increased in strength exponentially. C) has reversed direction many times. D) is unknown.

Q: Which force field can accelerate an electron? A) electric field B) magnetic field C) both of these D) neither of these

Q: Which force field can increase a moving electron's speed? A) electric field B) magnetic field C) both of these D) neither of these

Q: A beam of singly-charged ions entering a magnetic field are swept into circular paths. The wider paths are those of A) the lighter ions. B) the heavier ions. C) neither particularly.

Q: Although a magnet can change the direction of travel of an electron beam, it cannot change its A) speed B) kinetic energy. C) both of these D) neither of these

Q: A galvanometer can be calibrated to measure A) electric current. B) electric voltage. C) both of these D) none of these

Q: A galvanometer indicates A) electric charge. B) a flow of electrons. C) electric voltage. D) magnetic field strength.

Q: If a magnet produces a force on a current-carrying wire, the wire A) produces a force on the magnet. B) may or may not produce a force on the magnet. C) none of these

Q: No net force acts on a loop of wire in a magnetic field when A) no current is in the loop. B) no magnetic field lines pass through the loop. C) both of these D) neither of these

Q: An electron beam directed through a magnetic field A) may be deflected. B) may experience a force. C) both of these D) neither of these

Q: A current-carrying wire in a magnetic field A) may be deflected. B) may experience a force. C) both of these D) neither of these

Q: The force a magnetic field exerts on a current-carrying wire is maximum when the wire is oriented A) parallel to the magnetic field. B) perpendicular to the magnetic field. C) either of these D) neither of these

Q: The force exerted on an electron moving in a magnetic field is maximum when the electron moves A) parallel to the magnetic field. B) perpendicular to the magnetic field. C) either of these D) neither of these

Q: When an electron passes through the magnetic field of a horseshoe magnet, the electron's A) speed is increased. B) direction is changed. C) both of these D) neither of these

Q: The force on an electron moving in a magnetic field will be least when its direction is A) the same as the magnetic field direction. B) perpendicular to the magnetic field direction. C) either of these D) neither of these

Q: The direction of the force exerted on a moving charge in a magnetic field is A) in the direction of the motion. B) opposite its motion. C) at right angles to the direction of the motion.

Q: Into which stable force field can a proton be placed at rest without being acted upon by a force? A) magnetic field B) electric field C) both of these D) neither of these

Q: Compared to the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is A) relatively small. B) equally huge. C) inversely proportional to their masses.

Q: Magnet A has twice the magnetic field strength of Magnet B and at a certain distance pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is A) at or about 50 N. B) exactly 100 N. C) need more information

Q: The lift experienced by Maglev trains is due to magnetic A) attraction. B) repulsion. C) dipoles.

Q: A superconducting magnet uses A) iron cores. B) superconducting coils. C) both of these D) neither of these

Q: Place an iron rod inside a current-carrying coil of wire and you A) increase the strength of the electromagnet. B) have a superconducting magnet. C) a magplane in the making.

Q: A current-carrying coil of wire is A) a superconductor. B) a superconducting magnet. C) an electromagnet. D) a magplane in the making.

Q: A current-carrying loop of wire experiences no tendency to rotate in a magnetic field when A) field lines pass directly through the loop. B) no field lines pass through the loop. C) none of these

Q: A beam of electrons can pass through a magnetic field without being deflected if the direction of the beam is A) parallel to the field lines. B) perpendicular to the field lines. C) none of these

Q: A beam of electrons passing through a magnetic field experiences maximum deflection if the direction of the beam is A) parallel to the field lines. B) perpendicular to the field lines. C) none of these

Q: As the number of loops in a current-carrying wire is increased, the A) more spread out is the magnetic field. B) stronger the enclosed magnetic field. C) weaker the current. D) greater the back emf.

Q: When a current-carrying wire is bent into a loop, its magnetic field inside the loop A) weakens. B) becomes concentrated. C) cancels. D) none of the above

Q: When current reverses direction in a wire, the surrounding magnetic field A) also reverses direction. B) becomes momentarily stronger. C) contracts. D) expands.

Q: Magnetic field lines about a current-carrying wire A) extend radially from the wire. B) circle the wire in closed loops. C) both of these D) neither of these

Q: The shape of a magnetic field surrounding a current-carrying conductor is A) consistent with the inverse-square law. B) radial. C) circular. D) all of these E) neither of these

Q: Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a A) north pole. B) south pole. C) either of these D) neither of these