The physics knowledge of the third year of junior high school, help to solve it

1. Circuit breaking. 2. The voltmeter is short-circuited.

3. Short circuit of the whole circuit.

4. The voltmeter is connected in series with the power supply and the ammeter.

5. The electrical appliance is short-circuited.

6. Circuit breaker with electrical appliances.

1.There is an open circuit in the circuit in parallel with the voltmeter.

2.The voltmeter is disconnected. (If it is a short circuit, the current indication is very large)3Both the ammeter and voltmeter are connected in parallel with the power supply.

4.They may be wide together in series on the power supply, but the voltmeter range is less than the supply voltage.

5.There is no possibility, the unit of current is A, which can never be equal to the supply voltage.

6.It may be wide that they are connected in series together on the power supply, but the voltmeter range is greater than the supply voltage.

1. A circuit measured by the voltmeter is broken, forming a circuit connected in series with the ammeter.

2. If there is a short circuit in a circuit measured by the voltmeter and there are other resistors in the circuit, the ammeter will not be burned out.

3. There is a short circuit in a circuit measured by the voltmeter, and there is no other resistance in the circuit or other resistors are also short-circuited (if all are connected in parallel, the voltmeter has a reading, that is, the power supply voltage).

4. The ammeter and the voltmeter form a series connection and the voltage of a circuit measured by the voltmeter exceeds its range.

5. The circuit measured by the voltmeter is a series circuit between the resistance and the ammeter, and there is no other resistance, but there is no similarity between the ammeter reading and the power supply voltage.

6. Voltmeter, ammeter and resistance are connected in series.

Solution: (1) The total time from Shanghai to Nanjing is 1 hour and 57 minutes = hours.

The total mileage is 303 km.

The average speed is v = 90 km/h.

2) Shanghai to Suzhou speed v = kilometers per hour.

The speed from Suzhou to Changzhou is v=km/h.

The speed from Changzhou to Nanjing is v=101 km/h, which is the fastest in this section.

The train runs for 200 minutes and 303km, so the speed v=(303x1000) (200x60)= [this is the average speed].

In Changzhou, only the Nanjing section runs the fastest, and its speed reaches.

1.Chemical fuels (coal, natural gas, oil), carbon dioxide, sulfur dioxide, global warming.

1) an increase in pests and diseases on the planet;

2) sea level rise;

3) abnormal weather and an increase in ocean storms;

4) The land is arid and the area of desertification is increasing.

3.Water pollution, domestic sewage, industrial sewage, industrial solid waste, domestic waste.

4.Explosive proliferation of phytoplankton, protozoa, or bacteria in seawater is highly aggregated.

2.The density becomes larger.

Because the density of ice is less than that of water.

The original volume of the ice was v

The mass is m density = m v

When the ice melts partially, due to the ice turns into water.

So the volume decreases, but the mass remains the same.

So the density becomes larger.

1.The ball rolls on its own.

When the water level is smooth, the ball only sells gravity, so it will always move in a straight line at a uniform speed.

3.Because the top of the umbrella is bulging, the air becomes faster when it is left there, due to the gas and liquid.

The pressure at the high velocity is small, so the pressure at the top is smaller than the pressure at the bottom, and because the area of the top and bottom of the umbrella is the same. So according to f=s p

So the force of the bottom up.

is greater than the force from top to bottom, so the umbrella is jacked up.

1.The ball will continue to rotate due to inertia.

Because there is no external force to stop its rotation, the force is the reason for changing the state of motion of the object, the moment the ball rolls to a smooth horizontal plane, it rotates when it is in a state, so it will always rotate.

2.The physical meaning of invariant, density, is a property of matter.

3.When you hit the umbrella, the force of the umbrella is gravity, the friction of your hand against it, the two forces are balanced, when the wind blows, because there is only wind in the horizontal direction, the moment the wind blows the umbrella, pay attention to the moment your hand produces a pull force on the umbrella to prevent the umbrella from being blown away. The pull force is oblique downward, and the direction of the umbrella's fluttering is the opposite direction of the tension, and the pulling force is not increased at that moment but is controlled by the person's reaction time, so it will float backwards along the oblique, and when the pull force is large enough, it will eventually be used for the umbrella:

The combined force of tension and wind is the gravitational force of the umbrella.

1.Rolling down on an inclined plane, the potential energy is converted into kinetic energy, there is no friction in a smooth horizontal plane, according to the conservation of mechanical energy, the kinetic energy remains unchanged, so it does uniform linear motion, not because of inertia. (The same goes for swiping).

2.Get bigger. Because ice is denser than water, and the volume of water of the same mass is smaller than ice, the melting volume of ice becomes smaller and the density increases.

3.Because the flow velocity above the umbrella is larger than that below, and the flow velocity is large and the pressure is small, the umbrella is subjected to upward force and horizontal thrust, and the direction of the resultant force is oblique upward, so the umbrella floats obliquely upward.

The first question gives you a correct solution, completely depends on whether the inclined plane is smooth, the inclined plane is smooth, the whole process is sliding, and the inclined plane is rough, it is rolling.

1.Rolling, because there is a velocity, on a smooth horizontal plane, the ball is not affected by force in the horizontal direction, so it will move in a straight line at a uniform speed when it just enters the smooth horizontal plane, if the inclined plane is very rough, the speed when the ball slides to the smooth horizontal plane is zero, then the ball will be stationary, if there is still a velocity when entering the smooth horizontal plane, then it will do a uniform linear motion.

2.The density becomes greater because the density of water is greater than that of ice, so the volume of water of the same mass is smaller than that of ice, therefore, after the original ice melts slightly, the total volume becomes smaller, while the mass remains the same (without considering evaporation), so the total density becomes larger.

3.The reason why the umbrella floats obliquely upwards is as follows: first, the shape of the umbrella is convex and concave, which determines the horizontal wind, and the flow velocity above the umbrella is greater than the flow rate below, so the air pressure above becomes smaller, and the umbrella will float upward; Second, because the surface of the umbrella blocks part of the wind, the wind speed near the umbrella becomes smaller, so its air pressure is less than the wind behind, and the umbrella will tilt forward according to the principle of atmospheric pressure. Combining one and two, then the direction of the resultant force received by the umbrella is obliquely upward, so the umbrella will float diagonally upward.

Rated voltage, rated power, r=u p=220 1000=ohm.

The actual power is 1000W

At 110V, the actual power is 250W

19 Electricity consumption in a month of Senfeng.

20.21.Rong Fengchun unraveled.

22.No change.

f float = g23Wait for the silver to be taken in.

Pick B. Because after taking water and pouring it in, the small cup is heavier and will sink deeper, so the h will decrease.

The amount of water in the small cup increases the weight of this part, and the volume of the water discharged is just equal to the amount of water that is reduced outside, so h will not change.

You must know that the mass of the discharged liquid is equal to the buoyancy received, after taking out a part of the water, the buoyancy is unchanged, and then poured into a small container, the small container is still in a suspended state, buoyancy is equal to gravity, that is, the gravitational force increases, the buoyancy also increases, and the exclude liquid also increases!! It is impossible to find h and h without accurate data, unless you know the mass or volume of the liquid discharged!!

Because water is added to the container, the container sinks, just like adding an object denser than water to the water.

So h will increase and h will decrease, because because there is water in the container, part of it will sink in the water, so the part that is exposed on the water, that is, h, will decrease.

d, do you want to analyze, to explain to you, a if the resistance of the "two ends" of the power supply is zero, then the voltage at the "two ends" is still zero, and the current still exists. In this case, it is equivalent to a "short circuit", and the current is quite large, and the consumption in the power supply is the limit. B switch is disconnected, there is no current without forming a loop, C refers to B

a, node method.

a, look at the range of the meter to know that the meter is a voltmeter.

B, when S1 disconnects S2, the circuit belongs to the open circuit, the voltmeter measures the power supply voltage, S1 closes and S2 is disconnected is the voltmeter measures L1, and the subtraction can be known.

d, the ammeter has an indication that it cannot be an open circuit.

a. The voltage at both ends of each branch of the parallel circuit is equal.

C, a can be represented, b can't, d has a limit on the current ba (this question is uncertain, I think the last one is okay).

You're done with physics! Flip through the book by yourself.,The title is very jian d.

Child, study hard, do your homework well, and don't just think about asking others to help you with your problems.

There should be an answer, the question is very simple.