Physical issues about energized wires vs. wireframes .

The simplest example, you take 2 magnets, and they definitely follow the principle of opposites attracting, peers repelling. But you can't expect magnets and pieces of iron to follow this principle as well, because pieces of iron are not magnetic, they just attract. But the iron sheet can be magnetized, and the coil can be "electrified" by the energized wire, and as for the essential difference between the left-hand rule and the Lenz theorem, I forget, it's been a few years, so let's wait downstairs.

Intercepted on the Internet: This... Cause and effect, I can't finish talking about it in a few words... It is recommended that you take advantage of the holiday to read 3-2, start reading from the first page, see that you see the rule of the right hand, I believe you will be very clear when you think more, the rule of the left hand is in chapters 5 6 of 3-1, you can also look at it. I also flipped through it many times at the time.

Lenz's law is the direction of the induced current in a closed loop, which always causes the magnetic field it excites to hinder the change in the magnetic flux that causes the induced current. Do you understand this? There are experiments in the book, read carefully, compare carefully. You'll get the idea.

The right-hand rule is cut in the magnetic field of the conductor rod, as if Lenz's law is too troublesome to judge, so a right-hand rule is coming. For cutting, spread out your right hand so that the magnetic lines pass vertically through the palm of your hand, with the thumb of your right hand representing the direction of the cutting and the four-finger direction representing the direction of the current (this is the cause).

With the current, in the magnetic field (note that it cannot be parallel) will be forced, this is the left hand rule, but also spread the left hand, so that the magnetic inductance line perpendicular through the palm, the four fingers represent the current, the thumb is the force (this is the effect of the cause to have the effect of the current, provided that the circuit is closed).

That's pretty much it, look at the textbook, it's very detailed).

Choosing B, the essential difference is that the induced current, there is a current, and the magnetic field generated by the two is different. As the current decreases, the magnetic inductance lines coming out of the right side of the wire decrease, so the magnetic inductance lines are generated inward in the rectangle, and the current is clockwise.

But whether to be close or far away is related to the force, f=bil, from b outward, i up.

In the first frame, b generated by the current in l is inward and i is upward.

The left-handed rule judges force, Lenz's theorem: the direction of this current tends to prevent the change in the magnetic flux that produces the induced electromotive force.

I don't think there's anything to do between the two, it's just a matter of which one is convenient to do.

The magnetic induction intensity b2 produced by i at 2i is 1 2 of the magnetic induction intensity b1 produced by i i at i, i.e., b2 = b1 2.

It should be the same, this is according to Newton's third law, they belong to the action force and the reaction force, and they must be of the same magnitude. You can use f=bil to calculate this, but you ignore the fact that the magnetic field around them is different because the current in the two wires is different, and b is different, and you think b is the same, so you can conclude that the ampere force is different.

Because the forces between objects are reciprocal, satisfying Newton's third law, the action force and the reaction force are so opposite.

The ampere force on a wire with current i is the effect of the magnetic field produced by the wire with current 2i, and the magnetic field force experienced by 2i is the effect of the magnetic field produced by the current i on it, and b of the formula f=bil is not the same.

In your formula f=bil, i perceives the magnetic field produced by 2i, and 2i perceives the magnetic field produced by i. That is, for 2i, although the current is larger, the magnetic field it feels is smaller (because the current source that produces this field is only i), and similarly, for i, although it has a smaller current, it feels a larger magnetic field (because the current source that produces this field is 2i). The Biot-Savar law shows that the difference between the two magnetic fields is exactly 2 times, which cancels out the 2 times the current, so that the two wires are subjected to the same force.

Your problem is that you only take into account the difference in the size of i, and ignore the change in the size of b.

It happens through a magnetic field.

The interaction of electric current with electric current is not direct or indirect, but the action of force is generated by the magnetic field as a medium. The electric current first produces a magnetic field, and the property of a magnetic field that acts forcefully on the current in the magnetic field, such that another current is subjected to a magnetic field force (ampere force) in this magnetic field, and in the same way, another electric current produces a magnetic field, and another current is subjected to a magnetic field force in this magnetic field. The direction of the magnetic field generated by the current is judged by the right-hand rule, and the direction of the magnetic field force is determined by the left-hand rule, the current in the same direction attracts each other, and the current in the opposite direction repels each other.

The magnetic field is a special substance that cannot be seen or touched, the magnetic field is not composed of atoms or molecules, but the magnetic field exists objectively. The magnetic field has the radiative properties of wave particles. There is a magnetic field around the magnet, and the interaction between the magnets is mediated by the magnetic field, so the two magnets can act without contact.

An electric current, a moving charge, a magnet, or a special form of matter that exists in the space around the changing electric field. Since the magnetism of a magnet is the same as the current, the current is the movement of an electric charge, so in a nutshell, the magnetic field is generated by the change of the moving charge or electric field. From the point of view of modern physics, the only ultimate components that can form a charge in matter are electrons (with a unit negative charge) and protons (with a unit positive charge), so the negative charge is a point object with excess electrons, and the positive charge is a point object with excess protons.

The real source of the field where the moving charge produces the magnetic field is the magnetic field produced by the moving electrons or moving protons. For example, the magnetic field generated by an electric current is the magnetic field generated by electrons moving in a wire.

Select the direction of the magnetic field generated by the energized wire, you know the right-hand spiral rule (i.e., Ampere's rule), the direction of the magnetic field is from the right side of the wire in and out of the left side, and the closer to the wire, the greater the magnetic induction intensity.

a) The wireframe is translated to the left, and the magnetic field strength in the wireframe first increases, then decreases, then becomes larger, and then becomes smaller (anyway, it is changing), generating an induced current.

b) The wireframe is vertically translated towards the outside of the paper, which is similar to A.

c) Take the AB edge as the axis, and the CD edge rotates to the outside of the paper, but according to my guess, the distance between the wire frame and the wire will change when it is turned (the three-dimensional geometry will be the distance between the line and the surface), then there is an induced current.

d) The whole frame surface rotates with a long straight wire as the axis, the distance is constant, the magnetic field strength is constant, and there is no induced current.

a b c is right.

The condition for inducing the current is that the magnetic flux of the closed circuit changes.

D, the magnetic flux does not change. Or the number of magnetic field lines of the rectangular wire frame ABCD does not change.

A rectangular wire frame ABCD has a reduced number of magnetic field lines because the magnetic field is weaker away from the wire.

B is similar to A, but it is actually moving away from the wire.

Whether there is an induced current depends on whether the circuit is closed, to see whether the magnetic flux in the circuit has changed, if both are satisfied, then there is an induced current, because you did not send a picture, I can't judge, sorry.

C test question analysis: the energized straight wire produces a stable magnetic field, the farther away from the wire, the weaker the magnetic field, the more sparse the magnetic inductance line, so when the wire frame is far away from the energized wire, the magnetic inductance line through the wire frame is less and less, so the magnetic energy gradually decreases, so only option C is correct;

According to Ampere's rule, the magnetic field generated by the straight wire carrying a constant current is vertically outward in the direction of the left side of the wire, and the direction of the magnetic field on the right is perpendicular inward, and when the coil guide line is close, the magnetic flux through the coil becomes larger.

When the coil crosses the wire, the center axis of the coil coincides with the wire, and the magnetic flux passing through the coil becomes smaller, then the direction of the induced current is ABCDA, which is counterclockwise;

When the movement continues to the right, the magnetic flux through becomes larger, which can be found by Lenz's law, and the direction of the induced current is: ABCDA, which is counterclockwise;

When it is far away from the wire, it can be seen from Lenz's law that the direction of the induced current is: ADCBA, which is the clockwise direction; Therefore, ABC is wrong, D is correct, so D: D

a, the wire frame with the straight wire as the axis rotation, because the magnetic inductance line of the energized wire is a series of concentric circles with the wire as the axis, so the magnetic flux through the wire frame does not change, so there will be no induced current, so a is wrong;

b. The position of the two remains the same, so that the current in the straight wire is enhanced, the generated magnetic field becomes stronger, and the magnetic flux through the magnetic field increases, so there is induced electromotive force, there will be induced current, so B is correct;

c. The rectangular wire frame is far away from the energized straight wire, and the magnetic flux through the magnetic field decreases, so there is an induced electromotive force, and there will be an induced current, so c is correct;

d. The rectangular wire frame rotates with the AD side as the axis, and the magnetic flux through the magnetic field decreases, so there is an induced electromotive force, and there will be an induced current, so d is correct;

Therefore: BCD

As shown in the figure, the current of the straight wire, according to the right-hand spiral rule, can be seen that the magnetic field on the right side of the straight wire is perpendicular inward, and the magnetic field on the left is perpendicular outward, because it is at the midpoint of the wire frame, so the magnetic flux through the wire frame cancels each other out, and it is exactly zero; When the wireframe moves to the right, the magnetic flux on the left side of the straight wire perpendicularly inward through the wireframe decreases, and the magnetic flux on the right side of the straight wire vertically outward increases.

Therefore, b

The conductor frame cuts the magnetic inductance line to the right in the magnetic field, and the right hand rule determines that the direction of the current should flow from C to A. (The two sides of the wire frame are regarded as one side, and the current does not flow in the ** box, but flows in the brother hungry circuit composed of the ** box and the resistor r). Since the cutting direction of the two sides is the same, the direction of the two electromotive forces is the same, which is equivalent to two batteries in parallel.

So the parallel electromotive force does not change. Jointly power the r. These two electric envy positive returns will not be offset.

There are two sides here to cut the magnetic field lines, and both sides each produce the electric auspicious rough impulse potential of the BLV, which is equivalent to two electromotive forces for the power supply of the BLV in parallel to supply power to the resistor R. The current intensity of the stool is i=2blv r