AP Physics 2 : AP Physics 2

Study concepts, example questions & explanations for AP Physics 2

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Example Questions

Example Question #31 : Magnetism And Electromagnetism

Consider the given wire:

Electric_field_loop

In which direction should the electrons flow through the wire if the electric field generated inside the loop points out of the screen?

Possible Answers:

Out of the screen

Into the screen

Counterclockwise

Clockwise

None of these

Correct answer:

Clockwise

Explanation:

We need to use the right hand rule to solve this problem. However, the right hand rule applies to the flow of current, which is in the opposite direction of the actual flow of electrons (current is defined, in this case, as the direction of proton flow). Therefore, you can either use the right hand rule and reverse what you determine, or simply use your left hand.

Let's just use our left hand. Point your thumb out and curl your fingers. Your fingers should be pointing at you. This is the direction of the electric field when electrons are traveling the direction of your thumb. If you lay your left thumb along the wire loop on the left side of the loop, our fingers are inside the loop and pointing out of the screen. This is the scenario we are looking for. Therefore, the electrons need to flow clockwise around the loop.

Note that the electrons must flow through the wire, eliminating the answer options for "into the screen" and "out of the screen."

Example Question #1 : Right Hand Rule For Current Carrying Wire

You have two current-carrying wires layed parallel to each other like below.

Photo 3

Point R is halfway between each of the wires. If the wires carry the same current I, what is the direction of the magnetic field at point R?

Possible Answers:

Out of the screen

Left

There is no magnetic field at point .

Into the screen

Right

Correct answer:

There is no magnetic field at point .

Explanation:

Using the right hand rule, we can tell that the direction of the magnetic field due to the bottom wire is out of the screen. Likewise, we can tell that the magnetic field due to the top wire is into the screen. Because point R is halfway between the two wires, they each have the same strength. Therefore, they both cancel each other out, leaving no magnetic field.

Example Question #2 : Right Hand Rule For Current Carrying Wire

Physics2set1q7

In the figure above, there are two wires carrying different currents in the same direction. 

What is the direction of the magnetic field at point ?

Possible Answers:

Out of the screen

Into the screen

To the right

Downwards

Upwards

Correct answer:

Out of the screen

Explanation:

Physics2set1q7

Let's use the right-hand rule to determine the magnetic field cause by each current.

For current , we determine that the magnetic field is going into the screen.

For current , we determine that the magnetic field is going out of the screen.

Do the two directions cancel out? Well, the magnitude of  is greater than the magnitude of , meaning that  will overpower , so the net direction is out of the screen.

Example Question #4 : Right Hand Rule For Current Carrying Wire

Simple circuit mag field

In the given diagram, what is the direction of the magnetic field at a point ?

Possible Answers:

Into the screen

To the left

Towards the bottom of the screen

Out of the screen

To the right

Correct answer:

Out of the screen

Explanation:

Recall that the convention for the direction of current is from the positive end of the voltage source to the negative end (opposite the direction of flow of electrons). Thus, in this circuit the current is flowing counterclockwise from the voltage source. Using the right hand rule for the conventional current in the wire, the right thumb is pointed along the wire pointing to the left. At point the fingers curl around and point up, out of the screen. This can be verified by putting the thumb in the direction of current anywhere in the circuit. For example, if we take the direction of the current across the resistor, our thumb points down. Curling our fingers around the wire, the fingers will again point out of the screen at point , verifying our initial answer.

Example Question #683 : Ap Physics 2

Simple circuit mag field

In the given diagram, what is the direction of the magnetic field at a point ?

Possible Answers:

To the left

Towards the bottom of the screen

Towards the top of the screen

Out of the screen

Into the screen

Correct answer:

Into the screen

Explanation:

Current flows counterclockwise in this circuit. Using the right hand rule for the conventional current in the wire, the right thumb is pointed along the wire pointing to the left at the top of the circuit. At point the fingers curl around and point down, into the screen.

Example Question #1 : Right Hand Rule For Current Carrying Wire

Simple circuit mag field

What is the direction of the magnetic field at a point ?

Possible Answers:

Up towards the top of the screen

Out of the screen

To the left

To the right

Into the screen

Correct answer:

Into the screen

Explanation:

The current flows through this circuit counterclockwise. Using the right hand rule for the conventional current in the wire, the right thumb is pointed along the wire pointing to the right in the wire at the bottom of the circuit. At point the fingers curl around and point down, into the screen.

Example Question #2 : Right Hand Rule For Current Carrying Wire

The magnetic field of the earth points from geographic south to geographic north, indicating the the geographic south pole is actually a magnetic south pole. If this magnetic south pole were generated by current around the equator moving in a wire, which way would the conventional current be traveling?

Possible Answers:

None of these

South to north

East to west

West to east

North to south

Correct answer:

East to west

Explanation:

Visualizing a globe and pointing the thump "south" towards the "north" magnetic pole shows that the fingers curl and point from east to west.

Example Question #1 : Right Hand Rule For Charge In A Magnetic Field

Electrons are rotating counter-clockwise in the plane of the screen. What is the direction of the magnetic field at the center of rotation created by these electrons?

Possible Answers:

Right

Into the screen

Out of the screen

Left

There is no field at the center

Correct answer:

Into the screen

Explanation:

According to the right hand rule, counter-clockwise spinning charge would produce a field going out of the screen; however, because electrons are negatively charged, they produce an opposite field. Therefore, the field created by these electrons is going into the screen.

Example Question #2 : Right Hand Rule For Charge In A Magnetic Field

Metal

A piece of metal has a motional emf of  is moving through a magnetic field going into the page (depicted by the x's) with a magnitude of . The length of the metal piece (vertical length as opposed to horizontal length) is . Find the magnitude of the velocity of the object.

Possible Answers:

Correct answer:

Explanation:

The metal has free electrons which move through the magnetic field along with the metal. These are charges moving through a magnetic field. They feel a force acting on them

Using the right hand rule, it can be shown that the electrons will move to the top of the bar, leaving the bottom with a net positive charge. Now there is an electric field between the top and bottom of the metal bar. There is an electric force acting on the particles in the bar,

where  is the electric field. The electric force will now be equal and opposite the magnetic force so the charges will settle and not continue to move out of the bar. Setting these forces equal, the charge will divide out.

The electric field is just the motional emf per unit length,

Solving for v,

Example Question #2 : Right Hand Rule For Charge In A Magnetic Field

Suppose that an electron is traveling due east while in the presence of a magnetic field that is oriented such that it is pointing outward, away from the viewer. In what direction does the magnetic force on this electron point?

Possible Answers:

East

Away from the viewer

South

North

Towards the viewer

Correct answer:

South

Explanation:

In this question, we're presented with a scenario in which an electron is traveling east in a magnetic field that is pointing away from the viewer. We're asked to determine the direction in which the magnetic force on this electron points.

To answer this question, we'll need to use the "right-hand rule." This is a useful trick that allows us to relate the relative orientations of three quantities:

1) The velocity of a positively charged particle moving in a magnetic field

2) The direction of the magnetic field

3) The magnetic force experienced by the moving particle

In addition, there is an equation that relates these three quantities:

In such a situation, all three of the above quantities are oriented perpendicularly to each other. The right-hand rule is a useful way of remembering how each term is oriented with respect to each other. Using the right hand, the thumb represents the direction of the particle's velocity. The index finger represents the direction of the external magnetic field. And lastly, the direction that the palm is facing is the same as the direction of the magnetic force that is acting on the moving particle.

Keep in mind that these orientation are true for a positively charged particle. In order to determine the relative orientations of these terms for a negative particle, simply reverse the direction of the force.

In this problem, the particle is traveling east (to the right) and the magnetic field is pointing outwards, away from the viewer. Therefore, if we use our right hand and point our thumb towards the right and our index finger away from us, our palm is facing up. But since this is a negatively charged electron, we'll need to reverse the direction of the force. Hence, instead of pointing up (north) the force is pointing down (south).

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