Physics Chapters 36 and 37

Describe the 2 types of electron motion that produce the magnetic field in a bar magnet.

1) Electrons in constant motion about atomic nuclei and 2) electrons spinning about their own axes like tops

Faraday's law states that the induced voltage in a coil is proportional to the product of what 3 things?

1) The number of loops in the coil 2) The cross-sectional area of each loop 3) The rate at which the magnetic field changes within these loops

List 2 ways that magnets are like electrical charges.

1) They can both attract and repel without touching and 2) the strength of their interaction depends on the distance of separation.

What's the typical voltage to which a common neighborhood transformer steps down for houses and small businesses

120 volts

What's the typical voltage at which power is carried from power plants to cities

120,000 volts

Explain the law describe by Maxwell, a companion to Faraday's law

A magnetic field is created in any region of space in which an electric field is changing with time

Explain how the effect of magnetic forces on charged particles helps protect Earth from cosmic radiation.

Charged particles from outer space are deflected by Earth's magnetic field, reducing the intensity of the radiation

Describe what happens to the magnetic domains in an iron nail that's brought near a strong magnet.

Domains that are already oriented in the direction of the magnetic field grow, and domains that aren't aligned with the magnet's field rotate into alignment.

How can you make a permanent magnet weaker?

Drop or heat the magnet.

Explain why certain substances such as iron are magnetic but most substances aren't

Every spinning electron is a tiny magnet. In most atoms, the various fields cancel one another because the electrons spin in different directions. In iron and several other substances, the electron spins don't entirely cancel.

How do rock strata provide evidence that Earth's magnetic field isn't stable?

Iron atoms in a molten state tend to align with Earth's magnetic field. When the iron solidifies, the direction of the Earth's field is indicated by the orientation of the domains in the rock.

Describe what happens if you break a bar magnet in half and then brake each of the halves in half

Magnetic poles always exist in pairs, so each half still behaves as a complete magnet. If you break the halves in half, you'll end up with four complete magnets.

What's the name of the scientist who discovered the speed of electromagnetic waves

Maxwell

Describe some possible explanations for why Earth itself is a magnet

Most geologists think that moving charges looping around within Earth create its magnetic field. Another possible explanation is that convection currents in molten parts of Earth's interior, combined with the rotational effects of Earth, produce Earth's magnetic field.

If an ordinary iron nail is removed from a strong magnet, the nail will lose its magnetism. Why?

Ordinary thermal motion causes all or most of all the domains in the nail to return to a random arrangement.

How do you know if a diagram shows a current-carrying wire?

The diagram shows a current-carrying wire if the compasses are lined up with the magnetic field produced by the current and it isn't a current-carrying wire since there's no current in the wire so the compasses are aligned with the Earth's magnetic field.

What effect would an ion core placed inside the primary and secondary coils have on magnetic fields and the galvanometer reading

The magnetic fields around both cores would be stronger, and the galvanometer reading would show greater surges of current when the switch is opened or closed

Describe what happens if you place a magnetic compass near a bar magnet.

The needle of the compass lines up with the magnetic field around the bar magnet.

Explain the purpose of stationary contacts in a DC motor

The stationary contacts allow the current in the rotating loop to reverse during each half revolution. In this way, the current in the loop alternates so the forces in the upper and lower regions don't change directions as the loop rotates, resulting in continuous rotation.

Describe uses for superconducting electromagnets

They are used to guide high-energy particles around particle accelerators and MRI devices in hospitals.

Describe how the speed at which the person pushes the magnet affects the voltage that's induced in the coils

Very slow motion produces hardly any voltage at all. Guck motion induces a greater voltage

An example of a device functioning as both a motor and a generator is found in hybrid automobile. Explain this effect in acting as a generator

When braking or rolling downhill causes the wheels to exert a torque on the device, it acts as a generator and recharges the generator

An example of a device functioning as both a motor and a generator is found in hybrid automobile. Explain this effect in acting as a motor

When extra power for accelerating or hill climbing is needed, the device draws current from a battery which acts as a motor to assist the gasoline engine

Explain why producing voltage by pushing a magnet through a wire loop doesn't violate the law of conservation of energy

Work is done in pushing the magnet into the loop. The induced current in the loop creates a magnetic field that repels the approaching magnet

Electromagnet

a coil of current-carrying wire with many loops

Transformer

a device for increasing or decreasing voltage through electromagnetic induction. It works by inducing a changing magnetic field in one coil, which induces an alternating current in a nearby second coil.

What does an electric charge present where an electric field is created?

a force

Magnetic field

a force field that fills the space around a magnet.

Generator

a machine that produces electric current by rotating a coil within a stationary magnetic field

Describe how a sending antenna is used to produce radio waves.

a rotating device in the antenna alternately charges the upper and lower parts of the antenna positively and negatively. The charges accelerating up and down the antenna transmit electromagnetic waves

Galvanometer

a sensitive current-indicating instrument

Which statements are correct? a. Where the magnetic field lines are close together, the field strength is great. b. Where the magnetic field lines are far apart, the field strength is weak. c. Where the magnetic field lines are parallel, the field strength is zero. d. The field strength around a magnetic pole doesn't vary with distance.

a, b

which are things that happens at the moment the switch is closed in the primary circuit? a. A current flows in the secondary circuit b. A voltage is applied across the secondary circuit c. A magnetic field exists around a primary coil d. A magnetic field exists around the secondary coil

a, b, c, d

Which statements correctly describe electromagnetic waves? a. No medium is required to produce waves. b. The waves move outward in all directions from the vibrating charge that created them c. The electric field is parallel to the magnetic field in the waves d. Both electric and magnetic fields are perpendicular to the direction of the motion of the wave

a, b, d

Which are true about a current-carrying wire in a magnetic field? a. The force on the wire is maximum when the current is perpendicular to the magnetic field lines. b. The force on the wire is parallel to the current. c. If the direction of current in the wire is reversed, the deflecting force on the wire cancels to zero. d. If the direction of current in the wire is reversed, the deflecting force on the wire acts in the opposite direction

a, d

Almost all electric energy sold today is in the form of _____________

alternating current

If a galvanometer is calibrated to measure current, it is called a(n) _________. If a galvanometer is calibrated to measure electric potential, it's called a(n) ___________.

ammeter, voltmeter

What's the direction of the magnetic field that's created by a changing electric field

at right angles to the changing electric field

How fast does an electromagnetic wave move?

at the speed of light

Repel or attract? the north pole of a bar magnet near the south pole of another bar magnet

attract

What are the correct names of the 2 scientists who, in 1831, independently discovered that electric current can be produced in a wire by simply moving a magnet into or out of a wire coil? a. Einstein and Faraday b. Faraday and Henry c. Henry and Newton d. Maxwell and Newton

b.

Why would transmitting electric energy at low voltages result in large energy losses?

because of heating of the wires

Which ones are correct based on diagram B? a. The compass needles are aligned with the Earth's magnetic field. b. There's no current passing through the wire. c. At the location of each compass, the magnetic field produced by the wire is stronger than Earth's magnetic field. d. Charges moving through the wire produce a magnetic field pattern in the form of concentric circles about the wire.

c, d

Which things continue to happen as long as the switch is closed in the primary circuit. a. A current flows in the secondary circuit b. A voltage is applied across the secondary circuit c. A magnetic field exists around the primary coil d. A magnetic field exists around the secondary coil

c, d

According to Faraday's law, an electric field is created in any region in space where a magnetic field is ____________, and the magnitude of the electric field is proportional to ___________________

changing with time, the rate at which the magnetic field is changing

Magnetic Domains

clusters of atoms that have aligned magnetic fields

Power is transmitted great distances at high voltage and low ________

current

A motor converts ______ energy into ________ energy

electrical, mechanical

Power in a transformer is the rate at which _________ is transferred from one coil to the other

energy

true or false? A conducting wire experiences no deflecting force by a magnetic field as long as the wire carries current

false

true or false? Electricity is a source of energy

false

true or false? If a current-carrying wire is bent into a loop, the magnetic field strength inside the loop cancels to zero.

false

true or false? The speed of light depends on the frequency, wavelength, and intensity of the radiation

false

A step up transformer has a _____ number of turns on the secondary than on the primary. A step down transformer has a ____ number of turns on the secondary than on the primary

greater, lower

Electromagnetic Induction

inducing voltage by changing the magnetic field around a conductor

the primary coil is known as the

input coil

What's the other name for the generator effect

law of induction

How much force is exerted by the field on the particle (max, less than max, or zero)? Particle moves in a direction that's neither perpendicular nor parallel to the magnetic field lines

less than maximum

The discrepancy between the orientation of a compass and true north is called the ___________

magnetic declination

Regions that produce magnetic forces are called _______ _______

magnetic poles

How much force is exerted by the field on the particle (max, less than max, or zero)? Particle moves in a direction perpendicular to the magnetic field lines

maximum

A generator converts _________ energy into _________ energy

mechanical. electrical

The direction of the magnetic field outside a magnet is from the ______ pole to the ______ pole

north, south

the second coil is known as the

output coil

In both the motor effect and the generator effect, the moving charges experience a force that's ___________ to both their motion and the magnetic field they traverse

perpendicular

Repel or attract? the north pole of a bar magnet near the north pole of another bar magnet

repel

Repel or attract? the south pole of a bar magnet near the south pole of another bar magnet

repel

What happens when a radio wave hits a receiving antenna?

the electric charges inside the antenna vibrate in rhythm with the variations of the field

What would happen to an electromagnetic wave if the wave traveled greater than the speed of light

the fields would increase to ever greater magnitudes, violating the law of conservation of energy

The direction of force that a magnetic field exerts on a moving charged particle is always perpendicular to ___________________ and _______________________.

the magnetic field lines, the velocity of the charged particle

According to Maxwell, the magnitude of a created magnetic field is proportional to _______________________

the rate at which the electric field changes

The amount of current produced by electromagnetic induction depends not only on the induced voltage but also on what 2 things?

the resistance of the coil and the resistance of the circuit to which its connected

Of the 2 types of electron motion, which one is more important in term of the material's overall magnetic field?

the spinning of electrons about their own axes.

What would happen to an electromagnetic wave if the wave traveled at less than the speed of light

the wave would rapidly die out as the induced waves were weaker and weaker

Describe the Generator effect

the wire, with no current in it, moves downward through the magnet's magnetic field. the field exerts a force on the electrons along the direction of the wire, creating a current

True or false? Every magnet, regardless of its shape, has both a north and a south pole.

true

true or false? Just as a current-carrying wire will deflect a magnetic compass, a magnet will deflect a current-carrying wire

true

true or false? The difference between a piece and of ordinary iron and an iron magnet is the alignment of the magnetic domains

true

true or false? Voltage is induced whether the magnetic field of a magnet moves past a stationary conductor, or the conductor moves through a stationary magnetic field.

true

true or false? You induce the same voltage when you plunge a magnet in and out of a closed rubber loop as you do when you plunge the magnet in and out of a closed loop of copper

true

true or false? is it possible to produce electromagnetic waves by shaking a charged rod back and forth in empty space

true

Describe the Motor effect

when the current moves to the right in the wire, the magnet's magnetic field exerts a force on the moving electrons, and the wire is forced upward.

How much force is exerted by the field on the particle (max, less than max, or zero)? Particle is at rest in the field

zero

How much force is exerted by the field on the particle (max, less than max, or zero)? Particle moves in a direction parallel to the magnetic field lines

zero