Two parallel metal rails that are long enough in a uniform magnetic field and do not count the resis

Answer: Solution: (1) According to Newton's second law mgsin f = ma ......1 point).

f = μn ……1 point).

n = mgcosθ …1 point).

A = g (sin - cos) 1 point) is substituted for a = 10 ().

a = 4m/s2 ……1 point).

2) When the movement of the metal rod reaches stability, the speed is v, the ampere force is f, and the rod is balanced by force along the direction of the guide rail.

mg（sinθ-μcosθ）-f=0 ……1 point) At this time, the power p of the work done by the metal rod to overcome the ampere force is equal to the electrical power consumed by the resistor r in the circuit.

p = fv ……1 point).

It is solved by two formulas to ......1 point).

Substituting the known data into the above equation yields =10m s ......1 point) Finding the correct answer by other methods is also worth points).

3) Let the current in the circuit be I, the length of the metal rod between the two guide rails is L, and the magnetic induction intensity of the magnetic field is be=blv ......1 point).

…1 point) p i2r ......1 point).

The formula is .........1 point).

The direction of the magnetic field is ...... upwards in the plane of the perpendicular guide1 point).

1.Take g=10m s2

The resultant force is f=f1-f= down the inclined plane

The acceleration is a=fm=2ms2

When the velocity is stable, the sum of the ampere force f3 and the friction force f is equal to f1f3=f1-f=

The ampere power is equal to the power consumed by the resistor r.

p=f3v=

then v=20m s

If the power is 8W and the resistance is 2, the electromotive force is E=4Ve=Blvb=Elv=

There is no diagram, the direction is judged by the left-handed rule, anyway, the speed direction is down, the thumb direction is down, and the four-finger direction is pointing to b

1) When at rest, it is not subject to ampere force, but only gravity and support force, so the acceleration is provided by the component of gravity along the inclined plane. So we can find a=gsin37 degrees=6m s2(2) Because the circuit is a pure resistance circuit, by P = EI, and at this time the electromotive force E = BLV, P = BLVI, I = P BLV, the so-called speed stability is that the conductor rod does a uniform motion, the conductor rod is subjected to the balance force, then MGSIN 37 degrees = bil (ampere force), I is substituted into MGSIN 37 degrees = P V, and V = P MGSIN 37 degrees = 10M S.

This student, in the future, you should carefully analyze the meaning of the topic, and don't be afraid to substitute the unknown, as long as the idea is correct, the substitution of the unknown number is not terrible. If you think it is good, give it a good review and encourage it!

1) The initial velocity of the metal rod starting to slide is zero, according to Newton's second law: mgsin mgcos ma is solved by the formula A 10 ( 2 When the movement of the metal rod reaches stability, the velocity is v, the ampere force is f, and the rod is balanced by the force along the direction of the guide railmgsin a mgcos0 f 0 At this time, the power of the metal rod to overcome the ampere force to do work is equal to the electrical power consumed by the resistor r in the circuit: fv p is solved by , and the two equations are solved (3) Let the current in the circuit be i, and the length of the metal rod between the two guide rails is l, The magnetic induction intensity of the magnetic field is b p i2r and is obtained by , .

The direction of the magnetic field is ...... upwards in the plane of the perpendicular guide

You go and see it here.

It is important to know that the current in n is caused by the change of the external magnetic field, so the constant magnetic field generated when moving at a uniform speed will not cause the current of n.

And then the difference between slowing down to the right and accelerating to the right is what I said above. Do you think that the magnetic field caused by the induced current caused by the change in the pre-existing magnetic field caused by deceleration to the right and the acceleration to the right is the same? In other words, if a constant velocity to the right is added, a constant current will be generated in m, and there will be no changing magnetic field inside m.

There would be no current in n. Acceleration to the right and deceleration to the right will cause the current change rate in m to be positive and negative, resulting in the induced magnetic field being one inward and one outward, which is obviously different

If you know one thing, you can understand: that is, the magnetic inductance generated by the small coil is to prevent the change of the magnetic inductance of the large coil, that is to say, if the magnetic inductance of the large coil becomes larger, the small coil will produce the magnetic inductance in the opposite direction to prevent it from becoming larger, if the magnetic inductance generated by the large coil becomes smaller, the small coil will produce the magnetic inductance in the same direction to prevent it from becoming smaller.

The direction of the magnetic field inside the n-coil is inward, and the direction of the magnetic field outside is outward, which is the same as the direction of the magnetic field between the rails, so its magnetic flux becomes larger, and in order to prevent it from becoming larger, it is necessary to make its movement trend to the left, so accelerate to the left or decelerate to the right.

In the second question, although we don't know the specific direction of the magnetic field (only the plane of the vertical guide rail), we can use the law of slag to determine that the ampere force direction of the metal rod is parallel to the guide rail!

Because when the metal rod slides down the guide rail, the magnetic flux through the loop decreases, then the effect of the ampere force is to hinder the decrease of this magnetic flux, considering that the ampere force direction is perpendicular to the plane determined by the magnetic field and the current in the metal rod, so the ampere force direction must be parallel to the guide rail upward.

After the sliding speed of the rod is stable (sliding at a constant speed), the force of the rod is gravity mg, the support force n of the guide rail, the ampere force such as Hu Xing f (up along the guide rail), the sliding friction f (up along the guide rail), and the resultant force is 0.

So mg*sin f f

and f *n

n＝mg*cosθ

Get mg*sin f *mg*cos, that is, mg(sin cos) f 0, do you understand the pose?

The metal rod will be hindered by ampere force in the process of movement, so it cannot be a uniform motion, so AC is excluded;

Because the small closed coil n produces a clockwise current, there are two cases according to Lenz's law:

The current direction of the m-coil is clockwise, and the magnetic flux decreases.

The current direction of the m-coil is counterclockwise, and the magnetic flux increases.

Because the direction of the uniform magnetic field is perpendicular to the outward side of the paper, the first case is not true according to the left-handed rule, so the answer is D

i=e/(2r+r+r)=e/(4r)

The gravity of the rod is decomposed into two components, gx, parallel and perpendicular to the guide rail, gygx=mgsin

The rod remains stationary after being energized, so the ampere force f is balanced with gxbil=gx=mgsin

b=mgsin (il)=4mgrsin (ed) diagram doesn't the diagram draw the reverse of b, b, i, f know the two reverses, and find the third direction according to the left-handed rule.

The thermal power on the bar p=i r=e (16r).

Analysis: (1) By force analysis, according to Newton's second law, obtain: substitute data, solution.

2) When the sliding speed of the metal rod reaches stability, part of the gravitational potential energy of the metal rod overcomes the frictional force to do work and is converted into internal energy, and the other part overcomes the ampere force to do work and is converted into electrical energy, which is equal to the electrical work consumed by the resistor r in the circuit; Let the velocity be , in time, according to the conservation of energy, there is: Substituting the data, the solution is:

Use the right-hand rule to judge the direction of the magnetic field, and the plane of the vertical guide rail is upward.