Two physics sophomore electrical questions urgent! ）

Whether the power is the same or different, the result is different!

Analysis: (1) Simplify the circuit to know that 3 and 6 resistors are connected in parallel with the resistors in series, 5 resistors are connected in parallel with their equivalent resistors, and the ammeter measures the sum of the current of 5 resistors and the current of 6 resistors. The equivalent resistance of 3 and 6 resistors in parallel is 2.

So, 5 resistors are connected in parallel with 20 (2 +8 +10). 6. The voltage at both ends of the resistor is 18 20 2V. So the current representation should be 18 5A+

2。The answer is right. The power supply voltage can be set to U, with UR2 (R1+R2)=60V, U=3R1; The key is the following analysis:

Since R3 is connected in parallel at both ends of R2, the power consumption of the three resistors is equal, so R2=R3, the current through R1 is twice that of R2, there is a power formula P=i R to get R2=4R1, and substituting the data to solve the equation system can get U=75V, R1=25, R2=R3=100.

My mailbox.

The low wind and cold groaning are correct.

I would like to add to the second question of the first question.

When connected to the voltmeter, the circuit is: 10 and 8 in series for 18, 5 and 6 in series for 11, 18 and 11 in parallel, and then in series with 3.

You first calculate the current A through 3 and the current B through 6 respectively, and the voltmeter shows 3 A+6 B

Electrons do a flat-tossed motion in an electric field.

Vertical direction: t=lsin30° v0=5*10 (-9)s horizontal direction: lcos30°=1 2at 2

a= It's hard to type, do the math yourself.

a=qe/m

e = electrons are deflected to the right, so the direction of the electric field is in the -x direction.

(1) Let the electron charge e, the mass be m, and enter the initial velocity v0 of the deflection electric field, according to the kinetic energy theorem, there is eu1 = ......2 points) The flight time of the electron in the deflection electric field t1 = l v0 ......The acceleration of an electron in the deflected electric field a== ......In order for the electron beam to be deflected at the maximum distance on the phosphor screen, the electrons must be emitted along the edge of the lower plate after deflecting the electric field. The sideshift distance of the electrons in the deflected electric field is ......2 points) then there is: =at12......From:

Deflection voltage u2 = ......2 points) Substituting data to solve u2=205v (2 points) (2) Let the lateral shift distance of electrons after leaving the electric field be y1, then the maximum deflection distance of the electron beam on the phosphor screen is y=+y1......2 points) The lateral velocity vy = ...... of the electric field due to the deflection of electrons leaving2 points) The lateral displacement of the electron after leaving the deflected electric field y2=vy l v0......2 points) The maximum deflection distance of the electron is obtained by y=+......2 points) substituting data to solve y = points).

1. From the law of conservation of energy:

uql/d=mgl

The solution gives q=2, and the resultant force of the electric field force and the gravitational force is f. When the velocity of the ball is perpendicular to the direction of f, the angle between the direction of velocity and the direction of f is less than 90°, and the ball accelerates. When the velocity of the ball is perpendicular to the direction of f, the angle between the direction of velocity and the direction of f is greater than 90°, and the ball decelerates in motion.

So, when the ball velocity is perpendicular to the direction of f, the ball swing speed is the fastest.

Obtained from the conservation of energy:

mgl 2 2 = mv 2 + (1 - 2 2) * uql d solution v= (2 * ( 2-1) * gl).

If you still don't understand, you can ask, I hope it can help you.

What is the velocity of the ball as it slides to point B? If we set it to v, since the two points b and c are on the same equipotential plane, from b to c, the electric field force does not do work, and the kinetic energy of point c can be obtained to be equal to the kinetic energy of point b + gravitational potential energy (, so the velocity of point c can be obtained.

Since the velocity of point b is known, in the process of obtaining from a to b, the work done by gravity and electric field force is converted into kinetic energy at point b, and the work done by electric field force w can be obtained, and then according to w = qu, the potential difference between a and b can be obtained u

As in the second question, since the potential at point C is equal to the potential at point B is equal to 0, the potential at point A can be found.

The magnitude of velocity at point b is

Let's give an idea, from the perspective of mechanical energy from point A to point B, the energy of point B is the gravitational potential energy of point B + kinetic energy at this time, and the energy at this time - mechanical energy at point A = electric field force workmanship = qu; The potential difference can be found.

The electric field force values of the ball A to B and the ball B to C are equal, so the velocity of point C can be obtained by conserving energy.

This kind of question should tell us the speed of point B or point C, otherwise we can't find it.

If the velocity of B is known, only gravity and electric field do the work from A to C, and only gravity does the work from B to C. This problem is solved with the kinetic energy theorem.

The ball is at a critical point at p when the equivalent gravity is perpendicular to the direction of velocity.

Equivalent gravity provides centripetal force The equivalent gravity is 5 4mg = mv rv = 5 4gr

The kinetic energy is 1 2mv = 5 8mgr

P-point height 9 5r

The amount of change in electric potential energy provides gravitational potential energy and kinetic energy.

97/40mgr

The distance from A to P horizontally is 97 30R

The distance from P to B in the horizontal direction is 3 5R

So the distance from A to B should be 23 6R

This time it should be right.