# Physics Chapter 24 (MC+FR) – Flashcards

Flashcard maker : Jessica Forbes
The source of all magnetism is
A) tiny domains of aligned atoms
B) tiny pieces of iron
C) ferromagnetic materials
D) moving electric charge
E) none of the above
D – moving electric charge
Like kinds of magnetic poles repel while unlike kinds of magnetic poles
A) may attract or repel
B) repel also
C) attract
C – attract
Whereas electric charges can be isolated, magnetic poles
A) gather in clusters
B) can also
C) cannot
D) none of the above
C – cannot
Surrounding every magnet is
A) a magnetic field
B) an electric field
C) both of these
D) neither of these
A – a magnetic field
If you break a bar magnet in half you’ll
A) have two and a half magnets
B) have two magnets
C) destroy its magnetic properties
D) none of the above
B – have two magnets
The direction of the force exerted on a moving charge in a magnetic field is
A) opposite its motion
B) at right angles to the direction of the motion
C) in the direction of the motion
B – at right angles to the direction of the motion
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) exactly 100 N
B) at or about 50 N
A – exactly 100 N
Place an iron rod inside a current-carrying coil of wire and you
A) increase the strength of the electromagnet
B) a magplane in the making
C) have a superconducting magnet
A – increase the strength of the electromagnet
A beam of electrons 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
A – parallel to the field lines
Over geologic history, the Earth’s magnetic field
A) has reversed direction many times
B) is unknown
C) has been relatively stable
D) has increased in strength exponentially
A – has reversed direction many times
When an electron passes through the magnetic field of a horseshoe magnet, the electron’s
A) direction is changed
B) speed is increased
C) both of these
D) neither of these
A – direction is changed
Earth’s magnetic field is
A) protective to life on Earth
B) useful to pigeons but not to humans
C) something we’ve learned to live with
A – protective to life on Earth
The force on an electron moving in a magnetic field will be at least when its direction is
A) perpendicular to the magnetic field direction
B) the same as the magnetic field direction
C) either of these
D) neither of these
B – the same as the magnetic field direction
When current reverses direction in a wire, the surrounding magnetic field
A) expands
B) also reverses direction
C) becomes momentarily stronger
D) contracts
B – also reverses direction
The shape of a magnetic field surrounding a current-carrying conductor is
A) circular
B) consistent with the inverse-square law
D) all of these
E) none of these
A – circular
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
A – north pole
In the atoms of most materials, the fields of individual electrons
A) completely align
B) cancel one another
C) partly align
B – cancel one another
Magnetic domains normally occur in
A) copper
B) iron
C) silver
D) all of the above
E) none of the above
B – iron
The end of a compass needle that points to the south pole of a magnet is the
A) south pole
B) north pole
C) both of these
B – north pole
An iron rod becomes magnetic when
A) the net spins of many of its electrons are aligned
B) opposite ions accumulate at each end
C) its atoms are aligned
D) its electrons stop moving and point in the same direction
E) none of the above
A – the net spins of many of its electrons are aligned
If you place a paperclip near the north pole of a magnet, attraction will occur. Why will attraction also occur when you place a paperclip near the south pole of a magnet?
The domains (electrons) in the paper clip are induced into alignment (pointed in an opposite direction) in a similar to the electrical charge polarization of a neutral object when a charged object is brought nearby. Either pole of a magnet will induce alignment of domains in the paper clip.
Your study buddy claims that an electron always experiences a force in an electric field (i.e. when near a charged object), but doesn’t always experience a force in a magnetic field. Do you agree? Why or why not?
Yes, An electric field always acts on charged particles. The magnetic force vanishes when the velocity of the electron is parallel to the magnetic field.
A straight current-carrying wire is horizontal and oriented north to south. When a compass needle is place below or above it, in which direction does the compass needle point?
When placed above the needle points east and when placed below it points west. As you move the compass is goes in the direction of the magnetic field.
A beam of electrons passes through a magnetic field without being deflected. What can you conclude about the orientation of the beam relative to its magnetic field?
The beam is parallel to its magnetic field.
Can an electron at rest in a stationary magnetic field be set into motion by the magnetic field?
No, the electron has to be moving.
Two charged particles are projected into a magnetic field that is perpendicular to their velocities. If the particles are deflected in different directions, what does this tell you about them?
The charges of the particles are different.
One way to shield a habitat in outer space from cosmic rays is with an absorbing blanket of some kind (i.e. a layer of water), which would function much like the atmosphere which protects Earth. Speculate on a second way for shielding the habitat that would also be similar to Earth’s natural shielding.
A perpendicular field would also deflect it.
A magnet can exert a force on a moving charged particle but it cannot change the particle’s kinetic energy. Why not?
The magnetic force on a charged particle is perpendicular to the particles direction, so no work is done on the particle, therefore no change in kinetic energy.
Residents of northern Canada are bombarded by more intense cosmic radiation than residents of Mexico. Why is this so?
In Mexico, the Earth’s magnetic field lines are parallel to the surface and cosmic rays are bent away from the Earth. In Canada, the Earth’s magnetic field lines are nearly perpendicular to the surface (the North Magnetic Pole is in northern Canada), and charged particles such as cosmic rays follow the field lines toward the ground.
Why aren’t permanent magnets really permanent?
The magnet is “permanent” as long as nothing knocks its electrons out of alignment ie) other magnets, heat, vibration. But since it can be de-magnetized and re-magnetized, it is not really permanent.
A strong magnet attracts paperclips to itself with a certain force. Does the paper clip exert a force on the strong magnet? If not, why not? If so, does it exert as much force on the magnet as the magnet exerts on it? Defend your answers.
The paper clip exerts just as much force on the magnet because of Newton’s third law. The force the paper clip exerts is not as obvious because it doesn’t cause the magnet to move in any way (magnet’s mass is too large)
When iron-hulled naval ships are built, the location of the shipyard and the orientation of the ship in the shipyard are recorded on a brass plaque permanently attached to the ship. Why?
Ships have their own magnetic fields that vary due to the location of the shipyard and the orientation of the ship.
A beam of high-energy protons emerges from a particle accelerator. Do you suppose there is a magnetic field associated with these particles? Why or why not?
Yes, because moving charges create magnetic fields, and this situation includes moving positive charges.
What changes in cosmic ray intensity at the Earth’s surface would you expect during periods in which Earth’s magnetic field passed through a zero phase while undergoing magnetic pole reversal?
Increased intensity of cosmic rays.
A friend tells you that a refrigerator door, beneath its outer layer of white-painted plastic, is really made of aluminum. How could you check to see if this is true without scraping or otherwise damaging the door?
Place a magnet on the door. If it sticks, then it is an aluminum door.
Why will a magnet attract an iron nail or a paperclip, but not a wooden pencil?
A wooden pencil can’t align its atoms/domains
Your friend says that when a compass is taken across the equator, it turns around and points in the opposite direction. Your other friend says that this is not true, that people in the Southern Hemisphere use the south magnetic pole of the compass to point toward the nearest pole. What do you say?
Why is it inadvisable to make a horseshoe magnet from a flexible material?
A flexible material will stick to itself and make a circle
To make a compass, point an ordinary iron nail along the direction of the Earth’s magnetic field and repeatedly strike it for a few seconds with a hammer or a rock. Then suspend it at its center from a piece of string. Why does the act of striking the iron magnetize the nail?
It aligns the nail’s domains.
In what sense are all magnets electromagnets?
All magnetism is the result of moving charged particles.
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