Junior High School Physics Good Addition Junior High School Physics, Urgent Addition

Hello, see if I understand right:

Question 7: choose D:

It is known that: s d (thickness), f, n 90 (n: mechanical efficiency) from the meaning of the title, the force to be overcome in order to cut the nail moves:

Therefore w has fs

Then from n (w useful w total)*100 gets: w total w useful n is also the d answer in the question.

Question 8 choose C: 3, the detailed answer is as shown in the figure below, Question 9 choose B: (the key point is that "all can emit light normally") is equal to the logical understanding, because if one is only 100W, there are N, and the first one can emit light normally, then the total power in the circuit is of course 100Nw, easy to understand. It's really not credible, so I'll prove it to you with the actual lamp:

Suppose I have 10 lamps with 6V 3W (how many are the same), its resistance can be calculated by R U2 P, R U2 P 36 3 12 ohms, the following is divided into two situations to analyze:

1) Parallel: (shunt effect, i.e. i i1 + i 2) because each one can emit light normally, so the voltage is rated at 6V;

Each current is i p u 3w 6v, there are 10 pcs, so the total current is then the total power is: p ui 6v * 5a 30w.

2) Series connection: (voltage division, U1 U2), each rated voltage is 6V, the 10 are in series, that is 60V, the total resistance R total 12 ohm * 10 120 ohms, the total current is I total U total R total 60V 120 ohms.

Then the total power is: P UI 60V*.

Conclusion: Equal, choose B!

7 questions. The work done by the force is useful work, w=fs=

Total work w total = choose d

8 questions. Because the earth is spherical and electromagnetic waves propagate in a straight line, there are at least three, and there is no need to calculate, choose c

9 questions. The formula is used: p=u2 r, because the power supply voltage is unchanged, the parallel resistance is smaller than the series resistance, so the p of the parallel circuit is larger. That is, P A" P B, choose A

7 d, 8 c, because 3 can cover the whole earth.

9 b, because the electrical power of each bulb is equal, and the sum of n bulbs is also equal.

Generally, as long as 3 synchronous satellites at an angle of 120 degrees to each other can cover almost the entire earth. The calculations are complicated, so let's not talk about them.

It has nothing to do with temperature, not density, because density is a variable (i.e., a quantity that changes with the dependent variable), and it has nothing to do with the mass of the gas.

Explanation: Gases are composed of gas molecules that are not in contact with each other (due to the repulsion between molecules so that the molecules cannot be close enough, and because of the existence of molecular gravity, the molecules cannot be too far away), when the temperature rises, the force between the molecules (including gravity and repulsion) will increase, but the repulsion force is much greater than the change of gravity, so don't now macroscopic is what you said".But when heated, the air expands and becomes less dense,".

Due to the increase in repulsion, the pressure on the outer wall of the container increases.

Actually, you don't need to know so much, these are all high school knowledge. When you go to high school, you'll learn.

When you learn about the properties of gases in high school, you will understand. Here's a quick introduction:

For a certain amount of ideal gas, it has the following properties: p*v t=colonization p is the pressure. v is the volume; t is the thermodynamic temperature.

When the temperature rises, t increases, if v is constant; then p will inevitably increase. The reason for this is the acceleration of the thermal movement of the molecule. The fixed value is different depending on the mass of the molecule.

So the air pressure is related to the mass of the molecule. It is related to the density of the molecule.

Where to expand an airtight container? Misunderstanding of cause and effect.

p = ρgh

If GH is constant, atmospheric pressure is related to air density, temperature, humidity affect density.

There is not. What does it mean to be related to the mass of the gas (how much gas)?

Hihi, the volume of the gas expands when heated, because the mass does not change, the density becomes smaller, so the volume becomes larger, although the air pressure becomes smaller, but the distance between the molecules increases, of course, there must be a force to expand outside the cup, how can the pressure not be large.

The candle is amorphous, the flame core part is mainly to melt the candle and then vaporize it, the inner flame is the candle is not completely burned, and the outer flame part is completely burned, so the outer flame part has the highest temperature.

One end of the glass tube is placed in the center of the candle flame, and the candle will flow down the glass tube to the other end after vaporization, so the flame can also be ignited at the other end.

If the glass tube is inserted into the flame outside the flame, the candle will not ignite at the other end of the glass tube because it has completely burned.

When the candle burns, it also emits small solid particles (even if it is candle vapor), because the temperature is too high, and the volatilized paraffin vapor flows out of the glass tube, so it can be lit at the other end.

If it is placed in the outer flame, it cannot be ignited, because the vapor is emitted from the inner flame to the outer flame, so the vapor of the outer flame has already been burned, which is why the temperature of the outer flame is always higher than that of the inner flame.

It is paraffin vapor that does not burn.

No, the temperature is high and it has burned.

1) One of the two is 60w, right? The resistance of the filament thickness is small and the power is large, which is 60WThe voltage of the parallel circuit is the same, the power is large with small resistance, and of course the 60W filament is thick and bright. In series, on the contrary, the filament is thin and bright.

2) If you don't understand it, check it to see if it's a mistake. Being able to emit light doesn't mean anything.

3) r=u*u w, so the resistance of 8v is larger. The parallel power is U*U R, and the power with small resistance is large, so 6V3W is bright.

4) 5 3000*, so p=5 3000*

1) Ibid.

2) If it is connected in series, there must be a bulb that is short-circuited, but it does not affect. Because it is a partial circuit, Ohm's law does not consider the internal resistance, and the voltage at both ends of the circuit is 6V, which is normal light

3) Ibid.

Because: p=w t, w=fs

So: p=fs t=f*(s t)=fv

i.e.: p=fv

Deformation formula: f=p v

Because it is driving at a constant speed, f=f=p v=40000w (25m s)=1600n, (where 90km h=25m s).

W has = fs = 1600n 1800m = 2880000 ww total = q total = m steam q steam =

w has w total = 2880000w 11500000w 25%.

Time t=s v=

Work w = pt = 40kw * 72s = 2880 * 1000j force f = w s = 2880 * 1000j

Since the constant velocity drag is equal to f=1600n

w total = efficiency = w useful w total = 2880 * 1000j about =25%.

Resistance is the property of the object itself. It doesn't matter how much voltage it is, so it's always 3 ohms.

The resistance does not change, it should still be 3

The table tennis ball will not float until the mouth of the bottle is blocked, because the upper half of the ball is under the pressure of water, while the lower half of the ball is not under the pressure of water.

After the table tennis ball surfaces, the volume of the drained water decreases, and finally the buoyancy is equal to the gravity of the table tennis ball, which becomes floating. The reason is: after the bottle mouth is blocked, the lower hemisphere surface of the table tennis ball is subjected to the pressure of water, and this pressure is greater than the pressure on the upper surface, and the resultant force of the pressure on the upper and lower surfaces is the magnitude of buoyancy, so the reason for the buoyancy is the pressure difference between the lower surface and the upper surface.

This experiment is generally used to demonstrate the cause of buoyancy, and of course, in the laboratory, there is a device called the "Buoyancy Principle Experiment" that is better than this. It's just that this device is easy to take and easy to operate, and many junior high school physics teachers often use this experiment when talking about the causes of buoyancy.

1: Lamp resistance r = (u forehead) 2 p amount = (220v) 2 100w = 484 ohms.

2: Calculate the power displayed by the energy meter:

pSolid=wSolid=t= (20*60s)=121W;

Calculate the actual voltage: U real = root number (PR) = root number (121 * 484) = 242V;

3: Rated current of electric lamp: I = P = 100W 220V = Calculated total resistance: R total = u real I = 242V Euclidean string resistance: R string = R total - R lamp = Euro -484 Euro = Ω.

1: lamp r=u*u p=220*220 100=484 ohms2: calculate the power displayed by the energy meter: real p=(121 3000)*3600000 (20*60)=121 watts.

Calculate the actual voltage: SQRT (121*484) = 242V SQRT is the meaning of the root number;

3: Calculate the rated current of the lamp: i=p u=100 220=calculate the total resistance: total r = real p (i*i) = ohms.

String resistance: string r = total r - lamp r = ohm answer!

This is the resistance at "normal glow".

2。Actual power consumption: w = 121 3000kWh = p = w t = 14520j 1200s = 121wu = root number (PR) = 242V

3。The current in the "series resistance" (equal to the current at which the lamp normally emits), i=p u=100w 220v=5 11a

The voltage on the series resistance, U=242V-220V=22VThe magnitude of the series resistance, R=U I=22V (5 11A)=

1: R lamp = u amount i amount; i = p = u = > r light = u 2 p = 484 euros.

2: 121r p real * 20 60 = 3000r = > 121r * 3 p real = 3000r kw = >

P real = 121r * 3 3000r kw = (363 3000) kw = (363 3) w = 121w = >

U real = sqrt (p real * r lamp) = 242v

3: From the 1st and 2nd steps, it can be seen that when the normal light is emitted: I = p = p = 100w 220v = ; u = 220v = >

The voltage of the series resistance: U-string = 242V-220V=22V => R-string = U-string I = ohm.