Ask for junior high school physics problems, ask for advice, and expect an analysis process

1) When switch S1 is closed and S2 is disconnected.

In the circuit, R2 and the ammeter are broken, and the sliding rheostat R1 and lamp L are connected in series.

Because the small bulb glows normally.

i=p amount u=

u1 = u-u = 12v-6v = 6v

1 2r1=u1 i=6v ohms.

Then r1 = 48 ohms.

2) When the slide plate p of the sliding rheostat R1 is moved to the far left.

r1 = 48 ohms.

rl = u amount 2 p amount = 24 euros r total = rl + r1 = 72 euros.

i'= u r total = 1 6a

p real = i'^2rl=

3) When switches S1 and S2 are closed.

l Short circuit, R2 R1 in parallel, ammeter to measure the dry circuit current.

r total'=u/i''= 12v ohms.

1 r1) + (1 r2) = (1 r total).

Substitute the data.

r2 = 12 ohms.

Hope, thank you.

1) The resistance value of the bulb is r=u 2 p=24 ohms, and the voltage of the East China resistance is also 6 volts, so the midpoint of the sliding resistance is also 24, so the maximum is 28

Question 1c. Plane mirror imaging is equidistant from the "original image".

The second question is that the angle of refraction becomes larger.

Question 3b. Refer to question 2 for the rational analysis

The fourth question is the reflection of light, B is refraction, D is wrong, specular reflection will produce the so-called "reflection" phenomenon, that is, the screen cannot be seen clearly.

Question 5: White light through the three spirit realms is decomposed, c infrared d can not make light.

Question 6 d. Criticism and correction are welcome

The four on the left are parallel, and the one on the right is divergent.

ABCD draws parallel lines and E lines intersect in focus.

23, increase; Minish;

21, density; Vertical depth to the liquid surface.

20, p = f s = 0, 5 10-6 = 500,000 Pa.

1。Work done by tensile force: according to w=fs=50n*5m=250j

Gravity does work: 0j, because there is no distance to move in the direction of gravity, gravity does not do work.

2。According to w=fs: f=w s=300000j400m=750n

Solution: The work done by the tensile force w=fs=100*5j=500j

There is no displacement in the direction of gravity, so the work done by gravity is 0

Solution: The horizontal tensile force of the horse can be obtained from w=fs as f=w s=750n

The word is not good (1) w = FS = 50n * 5m = 250j w weight = 0j (self-done, this is the first question).

f=w s=3*10 to the fifth power 400m=750n

Classmates: You can understand =

Plastics: The hardness is good, light, but the high temperature resistance is relatively poor, and the high temperature is easy to produce chemicals and pollute the water.

Paper: light, non-polluting, but not strong enough, and not easy to reuse, can not be cleaned glass: heavier, beautiful, easy to clean, but fragile.

Aluminum: The weight is average, the strength is enough, but it is not easy to clean. And it cannot be filled with acidic water.

22 Question Answers: 1The reflected rays are in the same plane as the incident rays.

2.Satoshi, the reason is: if there is an angle of incidence, you may not see the angle of reflection, but when you see the angle of reflection, you must see the angle of incidence.

3.The reflection time path is reversible.