Q&A Hero

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) none of the above

Q: The magnetic field lines about a straight current-carrying wire are A) circular. B) radial. C) elliptical. D) spiral.

Q: The magnetic field lines generated by a bar magnet A) are external only. B) are both external and internal to the magnet. C) follow an inverse-square law. D) none of the above

Q: When a bar magnet is broken in half, the strength of the four new poles relative to pole strength before breaking is A) less than half. B) half. C) the same. D) somewhat more.

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

Q: A bar magnet that holds a chain of nails illustrates A) magnetic field displacement. B) magnetic induction. C) electromagnetic induction.

Q: An iron nail is attracted A) more strongly to the north pole of a magnet. B) more strongly to the south pole of a magnet. C) equally to either pole of a magnet. D) none of the above

Q: A magnet will become weaker if it is A) dropped on a hard surface. B) held in a hot flame. C) either D) neither

Q: Magnetic domains normally occur in A) iron. B) copper. C) silver. D) all of the above E) none of the above

Q: Wood does not have magnetic properties because it contains no A) iron or other metals. B) magnetic domains. C) moving electrons. D) none of the above

Q: A compass needle in a magnetic field experiences A) a torque. B) a net force. C) both of these D) none of the above

Q: An iron rod becomes magnetic when A) opposite ions accumulate at each end. B) its atoms are aligned. C) the net spins of many internal electrons are aligned. D) its electrons stop moving and point in the same direction.

Q: Magnetism is due to the motion of electrons as they A) move around the nucleus. B) spin on their axes. C) both of these D) neither of these

Q: Surrounding every moving electron is A) a magnetic field. B) an electric field. C) both of these D) neither of these

Q: Surrounding every stationary electron is A) a magnetic field. B) an electric field. C) both of these D) neither of these

Q: Every spinning electron is A) electrically charged. B) a tiny magnet. C) both of these D) none of the above

Q: A strong magnetic field easily penetrates A) human flesh. B) plastic coatings. C) both of these D) none of the above

Q: The ultimate source of all magnetism is A) tiny bits of iron. B) tiny domains of aligned atoms. C) ferromagnetic materials. D) moving electric charge.

Q: Compared with 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) not enough information

Q: Magnet A has twice the magnetic field strength of magnet B and pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is A) about 50 N. B) exactly 100 N. C) more than 100 N. D) not enough information

Q: If you break a bar magnet in half you'll A) destroy its magnetic properties. B) have two magnets. C) have four magnets. D) none of the above

Q: Refrigerator magnets are typically A) short range. B) long range. C) none of these

Q: Every magnet contains at least A) one pole. B) two poles. C) four poles.

Q: Like kinds of magnetic poles repel while unlike kinds of magnetic poles A) attract. B) repel also. C) may attract or repel.

Q: Unlike electric charges, magnetic poles cannot be A) located. B) isolated. C) destroyed.

Q: The rule for the interaction of magnetic poles is similar to the rule for electric A) circuits. B) polarization. C) charges.

Q: What is the connection, if any, between electromagnetic induction and sunshine?

Q: What correction do you suggest to a friend who states that a step-up transformer boosts energy, while a step-down transformer reduces energy in a circuit?

Q: How are electric motors and electric generators similar? Different?

Q: State and explain Faraday's law of induction.

Q: What happens to a current-carrying wire in a magnetic field? How does orientation of the wire make a difference?

Q: Distinguish between a common bar magnet and an electromagnet.

Q: What is the cause of a magnetic field about a permanent magnet and about a current-carrying wire?

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

Q: What any type of field generation cannot create is A) light. B) electromagnetic waves. C) energy.

Q: The frequency of a generated electromagnetic wave matches the A) field strength of the fields. B) energy of the fields. C) frequency of vibrating charges that produced it. D) frequency of domains in the magnetic part of the wave.

Q: Electric and magnetic fields combine to produce A) sound. B) light. C) both of these D) none of the above

Q: Induced electric and magnetic fields produce A) stronger electric or magnetic field. B) higher voltages produced by Faraday induction. C) both of these D) 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: Maxwell's counterpart to Faraday's law simply states that A) each change in one field induces the other. B) electric and magnetic fields are one and the same. C) induced fields are parallel to each other. D) all of the above

Q: The rapid change of an electric field induces A) a stronger electric field. B) a magnetic field. C) both of these D) none of the above

Q: The rapid change of a magnetic field induces A) an electric field. B) a stronger magnetic field. C) both of these D) none of the above

Q: A transformer has an input of 6 V and an output of 42 V. If the input is changed to 12 V, the output would be A) 12 V. B) 48 V. C) 84 V. D) more than 84 V. E) none of the above

Q: An electronic game requires 6 V for operation. With a transformer it can be powered by a 120-V outlet. If the primary has 500 turns, the secondary has A) 4 turns. B) 25 turns. C) 50 turns. D) more than 50 turns. E) none of the above

Q: A transformer for a laptop computer converts a 120-V input to a 24-V output. Compared with the number of turns on the primary coil, the secondary has A) 1/5 as many turns. B) 5 times as many turns. C) the same number of turns. D) none of the above

Q: A current of 4 A exist in the primary coil of a transformer powered with 110 V. What is the power output of the secondary coil? A) 27.5 W B) 110 W C) 440 W D) 880 W E) not enough information

Q: If the primary of a transformer were 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 as its input. C) that is also dc. D) only briefly while being connected or disconnected. E) none of the above

Q: An ideal transformer has 50 turns in the primary and 500 turns in the secondary. An input of 12 V will produce an output of A) 12 V. B) 120 V. C) 1200 V. D) none of the above

Q: An ideal transformer has 50 turns in its primary and 250 turns in its secondary. When 12-V ac is connected to the primary, the voltage available to the secondary is A) 5 V. B) 10 V. C) 30 V. D) 60 V.

Q: A certain transformer doubles input voltage. If the primary coil has 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: The voltage across the input terminals of a transformer is 110 V. The primary coil has 50 loops and the secondary coil has 100 loops. The output is A) 25 V. B) 55 V. C) 110 V. D) 220 V. E) none of the above

Q: The voltage across the input terminals of a transformer is 110 V. The primary coil has 50 loops and the secondary has 25 loops. The output is A) 25 V. B) 55 V. C) 110 V. D) 220 V. E) none of the above

Q: Compared with the current in the primary coil of a transformer, the current in the secondary coil A) is greater. B) is less. C) can be greater or less. D) none of the above

Q: The principal 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 for each set of loops or coils. D) none of the above

Q: A negatively charged rod is brought near a metal can that rests on a wooden table. You touch the opposite side of the can momentarily with your finger. The can then becomes A) positively charged. B) negatively charged. C) uncharged.

Q: Charge carriers in a metal are electrons rather than protons because electrons are A) negative. B) smaller. C) loosely bound. D) all of the above E) none of the above

Q: To say that electric charge is conserved means that no case has ever been found where A) the net charge on an object has changed. B) the net amount of charge on an object has increased. C) net charge has been created or destroyed. D) none of the above

Q: To say that electric charge is conserved is to say that electric charge A) occurs in an infinite variety of quantities. B) is a whole-number multiple of the charge of one electron. C) will interact with neighboring electric charges. D) can neither be created nor destroyed.

Q: If you strip electrons from an atom, the atom becomes a A) positive ion. B) negative ion. C) different element.

Q: When you scuff electrons from a carpet onto your shoes, you become A) negatively charged. B) positively charged. C) polarized. D) ionized. E) neutralized.

Q: As you comb your hair, electrons are rubbed onto the comb, which becomes A) negatively charged. B) positively charged. C) ionized.

Q: A rubber rod rubbed with fur becomes A) positively charged. B) negatively charged. C) both D) neither

Q: A positive ion has a deficiency of A) electrons. B) neutrons. C) negative ions.

Q: Which of these does not have an electrical charge? A) proton B) electron C) neutron D) all of the above E) none of the above

Q: In an electrically neutral atom the number of protons in the nucleus is equal to the number of A) electrons that surround the nucleus. B) neutrons in the nucleus. C) both of these D) none of the above

Q: An electron and a proton A) attract each other. B) repel each other. C) attract or repel depending on distance.

Q: Two positively-charged plastic straws near each other tend to A) attract each other. B) repel each other. C) neutralize each other.

Q: The fundamental force underlying all chemical reactions is A) gravitational. B) nuclear. C) centripetal. D) electrical. E) none of the above

Q: Which force binds atoms together to form molecules? A) gravitational B) nuclear C) electric D) centripetal E) none of the above

Q: When you remove electrons from a metal cup, the cup becomes A) negatively charged. B) positively charged. C) ionized.

Q: The vast numbers of electrons in a coin don't fly off the surface because A) mutual repulsion is incomplete. B) they are attracted by an equal number of protons. C) they are strongly bonded to their atoms. D) all of the above E) none of the above

Q: The pair of protons in the nucleus of a helium atom A) attracts a pair of orbiting electrons. B) repels orbiting electrons. C) both of these D) neither of these

Q: Which of these has the greatest mass? A) proton B) electron C) both of these D) neither of these

Q: Compared to the mass of a proton, the mass of an electron is A) very much less. B) identical. C) greater.

Q: The electric charge of all electrons A) vary from atom to atom. B) vary from ion to ion. C) are identical.

Q: The nucleus of an atom is charged A) positively. B) negatively. C) both of these D) none of the above

Q: Which of these scientists pioneered the study of electricity? A) Isaac Newton B) Galileo C) Benjamin Franklin D) all of the above

Q: A 60-W bulb and a 100-W bulb are connected in series in a circuit. Which draws more current? Which draws more current when connected in parallel?