How to make a liquid boil by cooling a vessel. Inventive problems How to make a liquid boil by cooling a vessel

Without a doubt, physics is one of the most interesting sciences. Even the most useless experiments can be quite fun at the same time. For example, the boiling of a liquid as it cools on one side seems incredible. After all, so that liquid boil it must be heated, but not cooled in any way, as we used to think. But anything is possible. This experiment does not require any special liquid, ordinary water will do, you just need to create special conditions.

You will need

Flask, water, gas burner, tripod.

Instructions

Pour ordinary tap water into the flask, fill it about half the level. After that, place the flask on a gas burner and heat the water until it boils.

When the water in the flask boils, turn off the heating and wait until the boiling stops. Seal the flask tightly with a rubber stopper and fix it in the tripod holder by turning it upside down.

Then start pouring cold water on the bottom of the flask. The better refrigerate vessel, the clearer the experience will be. Bubbles will rise to the surface of the water, the water in the flask will boil when cooled. This can be explained by the fact that the water vapor inside vesseland when cooled, they begin to condense on the walls of the flask. Because of this, the water vapor pressure inside the flask begins to drop. Under reduced pressure, water begins to boil not at a hundred degrees Celsius, but at a lower temperature. Since the water has not yet completely cooled down, and the pressure in vessele has fallen, and therefore boiling occurs on cooling.

note

It is best to use a thermally stable glass flask for this experiment. When a hot vessel is cooled with cold water, ordinary glass can crack from a sharp temperature drop and the experiment will not take place.

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For most children at school, physics lessons do not arouse much interest: the word "physics" is associated with complex problems and formulas. And the knowledge gained in the classroom is quite difficult to apply in practice, and this gives rise to a misunderstanding of the meaning of studying the subject. As a solution to this problem, as well as in order to form logical thinking and analysis, a set of "inventive problems" can be proposed. We usually gave them either at the end of the lesson, or in the "remaining five minutes," or as homework... For example, in the remaining 5-7 minutes of the lesson in the 10th grade, you can have time to solve one or two problems.

Since any work must make sense, children's interest can be stimulated by assessment. If the problem was asked at home, then for five different solutions to the problem - score "5", for every two additional solutions - one more score "5". If the task was given in the classroom, then the assessment was given to the most active students.

- Cover the vessel with a lid 2 ... Thus, to increase the pressure, and, consequently, the boiling point of water in it.

- Salt the water in the vessel 2 - the boiling point will also rise.

- Boil water in a vessel 2 several times, letting it cool between boils. Thus, we will remove impurities from the water (they will precipitate), and, consequently, the centers of vaporization, therefore, we will increase the boiling point of water.

- Place on the bottom of the vessel 2 ultrasonic generator.

- Place a copper rod in the water so that it rests against the bottoms of both vessels. In this case, we get a heat conductor.

- Wait until the water is in the vessel. 2 boil away.

- Pour into a vessel 2 liquid boiling at temperatures above 100 ° C.

- Heat the magnet. Thus, we will misorient the domains in the magnet.

- Heat the nail. Thus, we will misorient the domains in
nail.

- Use a lever made of wood or non-magnetic metal.

- Wind the wire around the nail and pass the current. Thus, turn the nail into a magnet of the same polarity with the ends of the horseshoe.

- Pull the nail sharply.

- Place the iron bar above the nail. Thus, we "short-circuit" the lines of magnetic induction and weaken the magnetic field at the ends of the magnet.

- Knock on the magnet. Deformation will lead to disruption of the ordered orientation of the domains in the magnet.

- Pump air into the flask. As you know, the arch is easy to break if you push from the inside.

- Place the entire system under the bell by plugging the tube and evacuate the air from the bell. Thus, we will create excess pressure in the flask, and it will burst, as in the previous case.

- Pour water into a flask and freeze. The flask will burst, because the water expands upon cooling.

- Heat the flask unevenly. Cool half of the flask, and heat the second. The flask will crack due to the difference in thermal expansion.

- Send a sound wave to the flask. The sound will make the walls of the flask oscillate, and at resonance the flask will burst.

- Put some more bricks on top.

- Hit the brick.

- Wait for the water to evaporate.

- Heat the mug to speed up the evaporation.

- Put a spoon in a mug and freeze. Then take out a spoon along with ice.

Note... Immediately after freezing, the spoon cannot be reached, so the edges of the mug will need to be slightly heated.

- Dip a sponge into the glass.

- Place the cocktail tube in the mug and suck out the water.

- Put the end of the long rubber tube into the mug, lower its other end below the level of the liquid surface and suck the air out of the tube - water will flow out.

- Place the tube in the mug, the other end of which is placed in a container with low pressure. Atmospheric pressure will drive the water into another vessel.

- Move the glasses relative to each other, turning one relative to the other.

- Wait a while. The system is not completely sealed and air still leaks through the gasket.

- Raise the temperature of the glasses, for example, pour boiling water over them. The gas pressure in the glasses will rise.

- Place the system under the bell and evacuate the air. The pressure in the glasses will be greater than outside.

How to divide an ice cube into two equal parts?

- Saw.

- Grind into crumbs and divide.

- Cut with a hot knife.

- Heat half.

- Melt the cube, divide the water in half, freeze the resulting halves.

- Place a support.

- Nail the legs to the floor.

- Experimentally select the angle of inclination so that equilibrium is established. Trim the chair legs at this angle to increase the footprint.

- Cut out recesses in the floor at an angle and insert the chair legs into them.

- Glue the chair.

How to make a mathematical matrix swing in only one plane?

- Spin the load around its axis. As a result, we get a gyroscope, and, as you know, the plane of rotation of the gyroscope does not change its position in space.

- Make an iron weight swing in a magnetic field.

- Construct a guiding structure (two plates).

- Make a metal weight swing in a static electric field (for example, between two charged balls).

- Fine tune at startup.

How to chill the water in the bottle?

- Put the bottle in the refrigerator.

- Put (on) under ice.

- Wrap the bottle with a damp cloth and place in a stream of air. When water evaporates from the surface of the rag, the latter will cool, taking heat away from the water bottle.

- Wrap the bottle with a damp cloth, place it under the bell and pump out the air. Thus, let us lower the pressure, and therefore accelerate the evaporation.

- Place the bottle in a container with colder water, such as ice.

- Chemically cool.

How to connect two metal plates?

- Use a bolt and nut.

- Use rivets.

- Glue.

- Solder.

- Cook. (Not all metals are welded - Ed.)

- Use electric spot welding.

- Grind and grind both surfaces to be joined and press firmly. (This is how cold welding is carried out in space. Ed.)

How to heat up a metal ball?

- Put in the oven.

- Bump.

- Rub for a long time.

- Deform.

- Pass the electric current.

How to speed up the drying of a damp cloth?

- Hang on a rope in a dry warm room.

- Expand it as much as possible.

- Place in a dry air stream.

- Place between dry rags (newspapers) and change periodically.

- Sprinkle a cloth with dry sand (sawdust), periodically shake it off and sprinkle again with a new portion of sand. The sand absorbs moisture.

- Place it near a powerful source of high frequency electromagnetic radiation. As a result of the action of Foucault currents, the liquid will be heated.

How to remove excess stone?

- Chip off with a chisel and hammer.

- Erase.

- Heat the stone and cool it sharply. As a result of the sharp temperature drop due to thermal expansion, the stone will crack.

- Cool and heat rapidly.

- Cut off.

- To melt.

What's the fastest way to fill a bucket in the rain?

- Place a bucket under the drain near the roof of the house. There, water is collected from a large roof surface.

- Place the funnel over the bucket.

- Put a cloth of fabric into the bucket with one end, and hang the other end. The water will drain from the fabric into the bucket (the area from which the water collects will increase).

- Place the bucket at an angle of 45 ° to the direction of the droplets falling. (It will be worse. - Ed.)

- Place several charges of the same name in the center of the bucket. As a result, the trajectory of the droplets will change.

How to raise the water level in the knee of a U-tube relative to the other?

- Pump out air from one knee and close this knee with a stopper.

- Pump air into one knee and close this knee with a stopper.

- Pour a lighter liquid (eg kerosene) into one elbow.

- Place the partition (piston) between the knees and move it, for example, on a thread.

- Use the phenomenon of osmosis.

How to make a car rolling off a hump to travel a greater distance by inertia?

- Nudge.

- Load the car.

- Lubricate the rails with oil, thereby reducing the coefficient of friction.

- Cool the rails. There is always water vapor in the atmosphere, condensation will appear on the cooled rails, which will reduce friction.

How to ensure the presence of water molecules at a height of 1 cm above the surface of the water in the vessel?

- Dip the wick into the water. Water molecules will rise through the capillaries.

- Throw ice into the water: it floats in the water, therefore, you can pick up a piece that will rise 1 cm above the surface, and ice is also water.

- Lower the sponge. The water will rise, as with the wick.

- Heat the water.

- Nothing to do. Water evaporates at any temperature, therefore, above the surface, at any or almost any height, there is at least one H2O molecule.

How to light up a small space?

- Light a match (candle, torch).

- Light it up with a flashlight.

- Ignite an electrical discharge.

- Excite luminescence.

- Excite the Cherenkov glow (the glow of water when particles pass through it at a speed higher than the speed of light in water).

How to speed up the boiling of liquid in a kettle?

- Increase heater power.

- Pour not water into the kettle, but a more easily boiling liquid (for example, acetone).

- Insulate the kettle, for example, wrap it in a thick cloth and a cotton blanket.

- Place the kettle in a low pressure area.

- Constantly knock on the kettle, thereby stirring the water.

How to stop a spring watch without damaging its outer shell?

- Do not touch the watch for a long time - they will stop themselves.

- Strongly shake, drop, hit.

- Dip in liquid and freeze.

- Place in liquid nitrogen.

- Place in an alternating magnetic field.

- Heat.

How to improve the glide of boots on ice?

Answer options

- Completely wipe off the outsole protector.

- Make the ice even, smooth.

- Make the ice surface moist.

- Pour oil over the ice.

- Attach runners to the boots (to make skates).

________________________

4th year student of VyatSGU, gave this material in 2005 in the classroom and extracurricular activities, passing pedagogical practice at school number 5 (Slobodskoy, Kirov region, head - Honored teacher of the Russian Federation Victor Ivanovich Elkin[email protected]). The students liked the problems very much, they solved them with pleasure.

You will need

Flask, water, gas burner, tripod.

Instructions

Pour ordinary tap water into the flask, fill it about half the level. After that, place the flask on a gas burner and heat the water until it boils.

When the water in the flask boils, turn off the heating and wait until the boiling stops. Seal the flask tightly with a rubber stopper and fix it in the tripod holder by turning it upside down.

note

\u003e\u003e Physics: Dependence of saturated steam pressure on temperature. Boiling

Liquid not only evaporates. It boils at a certain temperature.
Dependence of saturated steam pressure on temperature... The state of saturated vapor, as experience shows (we talked about this in the previous section), is approximately described by the equation of state of an ideal gas (10.4), and its pressure is determined by the formula

As the temperature rises, the pressure rises. Because the saturated steam pressure does not depend on the volume, then, therefore, it depends only on the temperature.
However, addiction r n.p. from T, found experimentally, is not directly proportional, as in an ideal gas at constant volume. With an increase in temperature, the pressure of a real saturated vapor grows faster than the pressure of an ideal gas ( fig. 11.1, part of the curve AB). This becomes obvious if we draw the ideal gas isochores through the points AND and IN (dashed lines). Why is this happening?

When a liquid is heated in a closed vessel, some of the liquid turns into steam. As a result, according to formula (11.1) the saturated vapor pressure increases not only as a result of an increase in the temperature of the liquid, but also as a result of an increase in the concentration of molecules (density) of vapor... Basically, the increase in pressure with increasing temperature is determined precisely by the increase in concentration. The main difference in the behavior of ideal gas and saturated steam is that when the temperature of the steam in a closed vessel changes (or when the volume changes at a constant temperature), the mass of the steam changes. The liquid is partially converted to steam, or, on the contrary, the steam is partially condensed. Nothing of the sort happens with an ideal gas.
When all the liquid has evaporated, the vapor, upon further heating, will cease to be saturated and its pressure at constant volume will increase in direct proportion to the absolute temperature (see. fig. 11.1, part of the curve Sun).
. As the temperature of the liquid increases, the rate of evaporation increases. Finally, the liquid starts to boil. When boiling, rapidly growing vapor bubbles are formed throughout the volume of the liquid, which float to the surface. The boiling point of the liquid remains constant. This is because all the energy supplied to the liquid is spent on converting it into steam. Under what conditions does boil start?
The liquid always contains dissolved gases released at the bottom and walls of the vessel, as well as on dust particles suspended in the liquid, which are centers of vaporization. Liquid vapors inside the bubbles are saturated. As the temperature rises, the pressure of saturated vapor increases and the bubbles increase in size. Under the action of the buoyancy force, they float up. If the upper layers of the liquid have more low temperature, then vapor condensation in bubbles occurs in these layers. The pressure drops rapidly and the bubbles collapse. The collapse occurs so quickly that the walls of the bubble, colliding, produce something like an explosion. Many of these micro-explosions create a characteristic noise. When the liquid warms up enough, the bubbles will stop collapsing and float to the surface. The liquid will boil. Pay close attention to the kettle on the stove. You will find that it almost stops making noise before it boils.
The dependence of the saturated vapor pressure on temperature explains why the boiling point of a liquid depends on the pressure on its surface. A vapor bubble can grow when the pressure of saturated vapor inside it slightly exceeds the pressure in the liquid, which is the sum of the air pressure on the surface of the liquid (external pressure) and the hydrostatic pressure of the liquid column.
Let us pay attention to the fact that the evaporation of a liquid occurs at temperatures lower than the boiling point, and only from the surface of the liquid, during boiling, vapor formation occurs throughout the entire volume of the liquid.
Boiling begins at a temperature at which the pressure of the saturated vapor in the bubbles is equal to the pressure in the liquid.
The higher the external pressure, the higher the boiling point... So, in a steam boiler at a pressure reaching 1.6 10 6 Pa, water does not boil even at a temperature of 200 ° C. In medical institutions in hermetically sealed vessels - autoclaves ( fig. 11.2) water boiling also occurs at elevated pressure. Therefore, the boiling point of the liquid is much higher than 100 ° C. Autoclaves are used to sterilize surgical instruments, etc.

And vice versa, reducing external pressure, we thereby lower the boiling point... By pumping air and water vapor from the flask with a pump, you can make the water boil at room temperature ( fig.11.3). When climbing mountains, atmospheric pressure decreases, so the boiling point decreases. At an altitude of 7134 m (Lenin Peak in the Pamirs), the pressure is approximately 4 10 4 Pa \u200b\u200b(300 mm Hg). The water boils there at about 70 ° C. It is impossible to cook meat under these conditions.

Each liquid has its own boiling point, which depends on the pressure of its saturated vapor. The higher the saturated vapor pressure, the lower the boiling point of the liquid, since at lower temperatures the saturated vapor pressure becomes equal to atmospheric. For example, at a boiling point of 100 ° C, the pressure of saturated water vapor is 101 325 Pa (760 mm Hg), and that of mercury vapor is only 117 Pa (0.88 mm Hg). Mercury boils at a temperature of 357 ° C at normal pressure.
A liquid boils when the pressure of its saturated vapor becomes equal to the pressure inside the liquid.

???
1. Why does the boiling point increase with pressure?
2. Why is an increase in the pressure of saturated vapor in bubbles essential for boiling, and not an increase in the pressure of the air present in them?
3. How to make the liquid boil by cooling the vessel? (This is not an easy question.)

G.Ya. Myakishev, B.B. Bukhovtsev, N.N. Sotsky, Physics Grade 10

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