Physics questions for junior high school! Urgent 10, junior high school physics questions! Urgent

1.The density of paraffin wax should be 900kg m3, and that of kerosene is 800kg m31) The density of paraffin wax is less than that of water, so floating on the surface of the water, it is subject to buoyancy equal to gravity.

f=mg=2) The density of paraffin wax is greater than that of kerosene, so the buoyancy of paraffin wax at this time should be calculated using Archimedes' principle.

v=m/p=

f=p*v*g=800kg/m3*

2.The method is the same as in the first question, as long as it is understood that when an object sinks and is completely submerged in a liquid, the buoyancy is calculated as f=p*v*g, and when it is placed in a liquid with a density greater than it, it floats, and the buoyancy is equal to its own gravitational force.

I hope it can help you, and I wish you progress in your studies!

It's so big. Density of paraffin? Wrong, right?

(1) Drain the air in the syringe.

2）..Tie the neck of the syringe piston with a thin nylon rope so that the other end of the rope is connected to the hook of the spring dynamometer, then slowly pull the syringe barrel horizontally to the right, and when the piston in the syringe is just pulled, write down the spring dynamometer indication f

3）..Read out the volume v of all the scales of the syringe, measure the length l of all the scales of the syringe with a scale, and calculate the cross-sectional area of the piston s=v l

4）..The atmospheric pressure p=f s=fl v(5) is calculated and the air is not exhausted.

When the piston is pulled, there is friction between the piston and the cylinder wall.

1. The rated voltage of the bulb is, so with a power supply of 6V, the function: with"10 1A "sliding rheostat series divider.

2. An ammeter used.

3. Use a voltmeter of 0-3V because: the number of electric expressions must exceed half of the selected range when measuring.

4、"10 1A "Slide Rheostats."

The bulb is rated for voltage so use a power supply of relative size (with"10 1A "sliding rheostat series subvoltage).

According to Ohm's law, a voltmeter of 0-3V is used, because the number of electrical expressions must exceed half of the selected range when measuring.

1. 6

2. 0-3a

3. 0-15a

4. 10ω 1a

One look at it tells that nothing else is enough!!

Personally think 6V power supply, ammeter, 0-15V voltmeter 1, 0 1A "sliding rheostat.

Using the knowledge of similar triangles to solve, I don't know if I have learned it now, I have not learned it, and this problem may be out of range.

There is no picture that can be drawn by yourself through the title.

At 5V, it is (R2 = 50 ohms from Ohm's law). At 3V, it is, (r2=6 ohms) The solution of a system of binary linear equations:

50 ohms + r2)* supply voltage.

6 ohms + r2)* supply voltage.

r2 = 5 ohms.

Supply voltage = OK!

Because of the series connection, the resistance is divided, and the larger the resistance, the greater the voltage representation. The lower the corresponding current.

So the maximum voltage corresponds to the minimum current, then the current is when the R2 voltage is 5V.

The rest is"Penguins meet polar bears"Write about those.

There is no question like this, ** and Mao is a good article.

Is this a test of my drawing skills?

When and are voltmeters, R1 R2 Rx series V1 measures R1 and R2 voltages.

V2 measures R2 and Rx voltages.

The ratio of voltmeter V1 and V2 is 7:12

So (R2+Rx) (R1+R2)=7:12 When and are both ammeters, R1 is short-circuited, R2 Rx is connected in parallel with A1 to measure the dry circuit current.

A2 measures R2 current.

The ratio of the ammeter A1 and A2 is 16:21

Underworld - Devil May Cry, have you ever studied physics? 1,2 is a pure series circuit when it is a voltmeter, and 1,2 is a pure parallel circuit when it is an ammeter, and you can see it clearly, it is R3, not Rx.

Almost the first and second years of junior high school are combined.

The mass of water m= v=

Heat absorbed by water q absorption = cm (t-t0) =

Excluding heat loss, Q = Q suction = pt to get t = q p =

It takes 20 minutes to boil the water at the rated voltage.