Physics Test 2

What is a magnetic dipole?

A magnetic dipole is made up of a north and south pole and no matter how many times you break it, you will always have a north and south pole. They are inseparable to each other and always come in pairs.

What is a magnetic domain?

A magnetic domain is a localized region inside a material where the magnetic dipoles of the atoms are all aligned.

What is the most significant difference between electric charges and magnetic poles?

A positive charge can exist all by itself, and the same is true of negative charge, but there are no magnetic monopoles! In other words, a N magnetic pole always exists in combination with a S pole.

You are given three pieces of wire that have different shapes (dimensions). You connect each piece of wire separately to a battery. The first piece has a length L and cross-sectional area A. The second is twice as long as the first, but has the same thickness. The third is the same length as the first, but has twice the cross-sectional area. Rank the wires in order of which carries the most current (has the lowest resistance) when connected to batteries with the same voltage difference.

A thicker wire will have a lower resistance and allow more current to flow with the same voltage across it. A shorter wire will also have a lower resistance and allow more current to flow with the same voltage across it.

Would you expect to find dc or ac in the filament of a lightbulb in your home? In the headlight of an automobile?

AC- lightbulb in your home DC- headlight of an automobile

What is the relationship between current, resistance, and voltage difference?

Current = Voltage Difference / Resistance

What's the difference between AC current and DC current? Which type of current flows through the simple circuit ?

DC stands for "Direct Current" because DC current always flows in the same direction around the circuit. DC current is caused by voltage sources that have constant polarity, like the battery in the simple circuit. AC stands for "Alternating Current" because AC current changes direction multiple times each second. AC current is caused by voltage sources that change polarity, like the wall plugs in your house.

Which of the following would double the amount of current flowing through a piece of metal wire?

Double the voltage across it.

During a magnetic pole reversal

During a magnetic pole reversal, the Earth's magnetic field switches direction but the Earth doesn't physically flip.

_______charges always produce _____ fields.

ELECTRIC ELECTRIC

How did we finally figure out the relationship between electricity and magnetism?

Electricity described by electric forces and fields by Coulombs and Gauss's Law. Magnetism described by magnetic forces and fields b Ampere's and Faraday's law.

If the resistivity of copper is less than that of gold at room temperature, which of the following statements must be true?

Electrons in gold are more likely to be scattered than electrons in copper at room temperature when they are accelerated by the same electric field.

List two similarities between electrostatic and magnetostatic forces.

Electrostatic and magnetostatic forces both come from static objects the force decreases as the distance increases.

Your friend says that a battery supplies the electrons in an electric circuit. Do you agree or disagree? Defend your answer.

I disagree because the wires supply the electric circuit.

Something gets "used up" in a battery that eventually dies and goes flat. One friend says that current is used up. Another friend says that energy is used up. Who, if either, do you agree with, and why?

I would agree with the friend that says the energy is getting used up bc the current is the rate that charge flows through the conducting wire. You need the energy to push it through.

Describe three ways that magnetic dipoles are produced inside an atom.

Magnetic dipoles are caused by the motion of electric charge. On the subatomic level, this can be caused by electron spin, nuclear spin and the "orbital" motion of electrons inside the atom. All three act like tiny "current loops" and therefore produce a magnetic dipole.

Explain why an electric shock is more likely to cause damage when your skin is wet.

Our body is a big resistor and when our skin is wet it lowers our resistances. When the resistances is lowered the voltage and current get much greater. Our skin provides most of the resistance to electric shock and being wet drastically reduces its resistance. The same voltage will provide a large current if our skin is wet and a small one if it is dry.

Why do some scientists suspect that the Earth is in the beginning stages of a magnetic pole reversal?

Over the last 20 million years, the Earth's magnetic poles have gone through a reversal about every 200,000 to 300,000 years. It's been more than twice that long since it hapenned so we are overdue for another reversal. The magnetic field is significantly weaker and the poles migrate faster and erratically compared to the periods between reversals.

Which of the following correctly describes the relationship between power, current and voltage?

Power = Current x Voltage

How do the resistances of two conducting wires compare if they have the same length, but one is twice the radius of the other?

The thicker wire has one-fourth the resistance of the thinner wire. A thicker wire will allow more current to flow with the same voltage difference driving it, because the resistance is inversely proportional to the area of the wire.

All atoms contain spinning charges, yet some atoms have strong magnetic dipole moments and others do not. Why?

The total magnetic dipole moment of an atom direction depends on the direction and alignment of the spinning charges inside it. Magnetic dipoles that are aligned add together to produce a stronger dipole. Dipoles that are anti-aligned tend to cancel each other out.

What does the voltmeter actually measure?

The voltage across its + and - terminals

List two similarities between electric charges and magnetic poles.

There are two types of electric charge and two types of magnetic poles. In both cases, opposite types attract one another and same types repel.

Why are thick wires rather than thin wires usually used to carry large currents?

Thick wires have less resistance and will more effectively carry currents without excessive heating.

The "I" in Ohm's law stands for_____ which is measured in _______.

current and amps

Most of the solar wind particles streaming toward Earth are

deflected by the Earth's magnetic field so that they flow around it like water going around a rock.

Open circuit

doesn't form a closed loop so no current will flow through the circuit.

Short circuit

doesn't have any resistance to impede the flow of charge so the current will be "infinitely" large

Identify the three basic requirements of an electric circuit. What does each one do?

1. The device that drops from high to low voltage 2. Closed loop- closed path to follow, no gaps 3. EMF source- pushes from low to high voltage

What is the current in a bulb if the resistance of its filament is 2 ohms and it is connected across a 6-volt battery?

3 amps

Why must an ammeter have almost zero resistance?

Ammeters are wired in series and adding a significant amount of resistance in series would change the current that the ammeter is supposed to be measuring. It would also change the voltages across the other elements of the circuit.

Open and Short circuit

An open circuit doesn't form a closed loop so no current will flow through the circuit. A short circuit doesn't have any resistance to impede the flow of charge so the current will be "infinitely" large.

In the circuit shown, how do the brightnesses of the identical lightbulbs compare? Which bulb draws the most current? What will happen if Bulb A is unscrewed? If Bulb C is unscrewed?

Bulb A and Bulb B have 2 times more resistances than Bulb C. Bulb C draws the most current and will shine brighter than Bulb A & B. If Bulb A is unscrewed then Bulb B & C will have the same current flow. If Bulb C is unscrewed then Bulb A & B will remain the same and the current flow will increase through as well.

How does the resistance of a thick piece of copper wire compare to the resistance of a thin piece of copper wire?

The resistance of the thin piece is greater than that of the thick piece.

Explain why a high voltage can be harmless while a small current may be fatal.

It is ok to touch a high voltage without touching the ground. When you touch the ground the current now has a path to travel through which is your body and it can be fatal if the current goes through your heart which means you have just made a closed circuit. Current equals voltage over resistance. If the voltage is low and the resistances is low if there could be enough current to kill you. The current is what kills you, not voltage.

What does the power company provide to our homes?

It provides energy to move the electrons.

Why must voltmeters have almost infinite resistance?

It's important that the voltmeter change the circuit as little as possible. However, voltmeters have to add a possible path for current since they must be wired in parallel. Having nearly infinite resistance means that the current through the voltmeter is nearly zero and therefore minimizes its affect on the rest of the circuit.

All ______ fields are produced by magnetic _____

MAGNETIC DIPOLES.

Only ______ charges produce magnetic ______.

MOVING DIPOLES.

The magnetic field exerts magnetic forces that pull the N pole of the magnetized needle generally northwards. Does this mean that the needle will move toward the north side of the bowl? Why or why not?

No, the magnetized needle will not move toward the north side of the bowl. The force that the needle exerts on is for both north and south pole which means it will not move so that means it is zero.

The monkey's uncle rides up to you on a Harley and says "Don't listen to that silly monkey! A compass does point to the nearest geomagnetic pole but when you're above the equator, you use its N pole to find north and when you're below the equator, the S pole points south." What doesn't the monkey's uncle understand?

No, the monkeys uncle is not correct and is confused because it doesn't matter if your above or below the equator for the compass will still align with the magnetic field.

Which of the following are more likely during a magnetic pole reversal?

The Earth's magnetic field lines isn't likely to resemble that of a magnetic dipole during a magnetic pole reversal so our compasses probably won't work properly. The weakened magnetosphere will allow more of the solar wind particles to leak into our atmosphere. This will probably cause amazing auroral displays at the poles, and aurora will probably occur at lower latitudes than is usual. Our electric grid is subject to disruptions during times of heightened solar activity. If the Earth's magnetosphere is greatly weakened, these disruptions are more likely to occur. And satellites that don't have the protection of our atmosphere will be more at risk to damage from the solar wind. We'll have to find a way to sheild them both.

Why doesn't the Earth's magnetic field look like the simple field of a bar magnet?

The Earth's magnetosphere is constantly blasted by the solar wind. The magnetosphere is compressed in the front region where the incoming solar wind hits the Earth's magnetic field. The magnetic field deflects the incoming particles so that they flow over and around the magnetosphere causing it to stretch back away from the Sun in a long tail.

Do the poles of a horseshoe magnet attract or repel each other? What happens to the size of the force as the poles get closer together?

The N and a S poles of a horseshoe magnet attract each other. The closer together the poles, the stronger the force.

What are the Van Allen Radiation Belts and where are they located in the figure?

The Van Allen Radiation Belts are the two blue "wings" extending outward from either side of the Earth in the figure. They are the regions where solar wind particles that do get inside the magnetosphere are trapped.

What quantity is ALWAYS the same no matter what you plug a light bulb into?

The amount of resistance it has

What are the "auroral" lights? What causes them and where do they mostly occur?

The auroral lights are mostly seen along the rings around the Earth's poles where the magnetic field lines intersect its atmosphere. They occur when charged particles from the Van Allen Radiation Belts leak into the Earth's upper atmosphere and collide with the particles in the air, causing them to "glow."

The light bulb will eventually "consume" all of the electric potential energy stored in the battery yet this doesn't violate the Law of Energy Conservation. Why?

The battery holds the energy and it pushes the current through the wires which makes the light bulb hot and light up. Eventually it consumes all of the electric potential energy that the battery has stored. Light bulbs transform the electric potential energy supplied by the battery into light and heat. The Law of Energy Conservation isn't violated because the total amount of energy remains the same.

How does the current change if you increase the resistance, keeping the voltage difference the same?

The current decreases

What does the ammeter actually measure?

The current passing between its + and - terminals.

Simple Circuit

The free electrons are supplied by the wire. The resistance is supplied by the light bulb. The voltage is supplied by the battery. The battery imposes a voltage (i.e. potential difference) across the light bulb. The voltage "pushes" the free electrons that are already in the conducting wires, making them move around the circuit. The motion (i.e. current) of free electrons is impeded by the resistance of the light bulb.

What does a magnetized object look like on a microscopic level? How is this accomplished?

The magnetic dipoles of all the atoms in a magnetized object are aligned. This is accomplished by placing the objects in a magnetic field.

A monkey with a compass rides up to you on a unicycle and says "A compass needle always points toward the nearest magnetic pole. When you're above the equator, it points toward magnetic north but if you go below the equator, it turns and points toward magnetic south." Do you agree with the monkey? Why or why not?

The monkey is wrong because the compass needle cause the needle to become aligned with the magnetic field. The north pole of the needle will and that means that it will point away from the north pole of the magnetic field but not the geographical North pole.

Is the resistance of a 100-W bulb greater or less than the resistance of a 60-W bulb? Assuming the filaments in each bulb are of the same length and made of the same material, which bulb has the thicker filament?

The resistance of a 60 W bulb is greater than the resistance than a 100 W bulb. The filament in the 60 W bulb is thicker and it will be brighter than the 100 W bulb. Increasing the power increases the resistances.

Non-magnetic material can be magnetized but it can't produce a magnet. Why?

When removed from a magnetic field, the magnetic dipoles of a non-magnetic object return to their random orientations. Only magnetic materials remain permanently magnetized once removed from the magnetic field.

Describes what would happen if you accidently wired voltmeter in series?

Wiring a voltmeter in series adds an infinite amount of resistance to the circuit, which makes the equivalent resistance of the circuit become nearly infinite. The voltmeter acts like a gap that current can't pass through so the circuit behaves like an open circuit and the current therefore drops to zero.

Describe what would happen if you accidently wired an ammeter in parallel?

Wiring an ammeter in parallel would create a short circuit because it would provide a path of nearly zero resistance for the current to follow. The current through the battery and ammeter would be nearly infinite, and the battery would be quickly drained.

Are these three circuits equivalent to one another? Why or why not?

Yes, these three circuits are examples of parallel circuits. It doesn't matter what different shapes of the wiring to the light bulbs are presenting because they are all coming out of the same voltage and they will all still be the same.

The needle of a magnetic compass ALWAYS

aligns itself with the magnetic field.

What kind of current runs through the electric wiring in a home?

alternating current

What factors does the resistance offered by a piece of conductor depend upon?

both the geometry and the material of the conductor

What type of field causes the electrons to do what they do in the wire?

electric field

The solar wind consists primarily of

electrons, hydrogen ions (protons) and helium ions which are also called alpha particles. It also contains trace amounts of heavier ions like carbon, nitrogen, oxygen, neon, magnesium, silicon, sulpher and iron

Resistivity

is a property of the material independent of its shape (dimensions). It is more and more difficult for electrons to travel through the material with a higher resistivity.

solar wind

is a stream of charged particles from the Sun

Of what physical quantity is Hertz a unit of?

number of times per second that the electrons move back and forth in the wire

Is the voltmeter wired in series with the bulb and battery or in parallel?

parallel

The "R" in Ohm's law stands for _____ which is measured in ____.

resistance and ohms

According to Ohm's law, MORE _____ produces LESS _____.

resistance current

Is the ammeter wired in series with the bulb and battery or in parallel?

series

magnetosphere

surrounding a planet is called its magnetosphere. it is the region where the planet's magnetic field is stronger than all others.

Which of the following are Ohm's Law?

voltage = current x resistance, which can also be written as current = voltage / resistance.

According to Ohm's law, MORE _____ produces MORE ______.

voltage Current

The "V" in Ohm's law stands for _____ which is measured in _____.

voltage and volts