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chp 24 h/w
Terms in this set (30)
By whom, and in what setting, was the relationship between electricity and magnetism discovered?
Hans Christian Oersted in a classroom demonstration
The force between electrically charged particles depends on the magnitude of each charge, their separation distance, and what else?
What is the source of the magnetic force?
Electric charges in motion are the sources of magnetic forces.
How is the rule for the interaction between magnetic poles similar to the rule for the interaction between electrically charged particles?
Like poles repel, unlike poles attract, and the force is proportional to the inverse square of the distance between two poles.
In what way are magnetic poles very different from electric charges?
All magnets have both south and north poles. Electric charges can exist as singular entities.
How does magnetic field strength relate to the closeness of magnetic field lines about a bar magnet?
The field strength is stronger where the field lines are closer.
What produces a magnetic field?
Electric charges in motion
What two kinds of motion do electrons in an atom appear to have?
Revolution and spin
What is a magnetic domain?
Clusters of atoms with their magnetic fields aligned
At the micro level, what is the difference between an unmagnetized iron nail and a magnetized iron nail?
In an unmagnetized nail, the magnetic domains have a random orientation so that the net magnetism adds to zero. In a magnetized nail, many of the magnetic domains are aligned.
Why is iron magnetic and wood not?
The magnetic fields of individual iron atoms are strong enough to align the magnetic fields of neighbor atoms. The atoms in wood have much weaker magnetic fields.
Why will dropping an iron magnet on a concrete sidewalk make it a weaker magnet?
Vibrations provide energy to randomize the magnetic directions of the domains.
In Chapter 22, we learned that the direction of the electric field about a point charge is radial to the charge. What is the direction of the magnetic field surrounding a current-carrying wire?
The magnetic field is directed along concentric circles surrounding the wire.
What happens to the direction of the magnetic field about an electric current when the direction of the current is reversed
The magnetic field reverses direction at every point. A clockwise pattern of concentric circles becomes a counterclockwise pattern of concentric circles and vice versa.
Why is the magnetic field strength greater inside a current-carrying loop of wire than about a straight section of wire
The magnetic field of each segment of wire in the loop, due to electrons moving in the wire, adds together inside the loop, thereby making the field become bunched-up.
Why does a piece of iron in a current-carrying loop increase the magnetic field strength?
The electromagnetic field of the current-carrying loop is amplified because it aligns the domains in the iron.
Why are the magnetic fields of superconducting magnets often stronger than those of conventional magnets?
Conventional magnets based on iron have a maximum magnetization that occurs when all of the domains are aligned. This saturation magnetization is weaker than the magnetic field of superconducting coils.
How is the magnetic force on a particle moving in a magnetic field different from gravitational and electric forces
Gravitational and electric forces act along the line connecting two interacting objects, whereas magnetic forces are perpendicular to the motion of the particle and the magnetic field.
In what direction relative to a magnetic field does a charged particle move in order to experience maximum deflecting force? To experience minimum deflecting force?
Perpendicular for maximum force, parallel for minimum force
What effect does Earth's magnetic field have on the intensity of cosmic rays striking Earth's surface?
It reduces the intensity.
What relative direction between a magnetic field and a current-carrying wire results in the greatest force?
The wire should be perpendicular to the field.
How does a galvanometer detect electric current?
An electric current flows through a wire in a magnetic field. The deflection force on the wire acts against a spring. The compression of the spring is proportional to current.
What is a galvanometer called when it has been calibrated to read current? When it has been calibrated to read voltage?
How often is current reversed in the loops of a simple dc electric motor?
It reverses twice each cycle.
Is it correct to say that an electric motor extends the physics that underlies a galvanometer? Why?
Yes. The deflection forces are the same, but the direction of current in the motor is reversed cyclically
Why are there probably no permanently aligned magnetic domains in Earth's core?
The core is too hot to allow atoms to maintain a constant magnetic orientation.
What are magnetic pole reversals?
The poles of the Earth's magnetic field undergo reversals.
What is the cause of the aurora borealis (the northern lights)?
The Earth's magnetic field guides trapped charged particles to follow field lines toward the poles, where they collide with the atmosphere, causing a glow.
Which of the following are creatures that are known to harbor tiny magnets within their bodies?
Bacteria, pigeons, bees, wasps, monarch butterflies, and sea turtle
When do cosmic rays penetrate your body?
All the time