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Acoustic phenomenon
1. The spread of sound
The object must vibrate when it sounds, and the vibration stops.
Sound transmission depends on the medium, and vacuum cannot transmit sound.
Usually the speed of sound is 340m/s, and the speed of sound is faster in solid than in liquid.
2. Sound characteristics
There are three types of sound characteristics: pitch, loudness and timbre.
The speed of the object's vibration corresponds to the height of the pitch.
The frequency of vibration (number of times) per second, and the unit of frequency is Hertz (Hz).
The human hearing range is 20 to 20000 Hz.
The amplitude of the object, the loudness of the sound.
Different sounds are distinguished, and sound waves have different timbres.
3. Noise hazards and control
Hinder people from taking breaks and learning work sounds,
Interference with listening sounds is common noise.
The sound level is decibel (dB), and it is 0 when the weak sound is just heard.
In order to protect hearing, the sound should not exceed 90 (dB).
Ensure that work and study, the sound does not exceed 70 (dB).
Ensure rest and sleep, and the sound does not exceed 50 (dB).
There are three stages of noise reduction: sound source, propagation and human ears.
There are two types of sound utilization, conveying information and energy.
Light phenomenon
1. Spread of light
Able to shine is called a light source, the moon is not the sun.
Conditions for the propagation of light are only straight lines for homogeneous media.
The speed changes in different objects, and the vacuum is 300,000 (kilometers) per second
C=3×105km/s=3×108km/s。
The speed of light is faster than sound, and vacuum light does not go away.
2. Reflection of light
The normal passes through the incident point, and the dashed line is perpendicular to the reflecting surface.
The reflected incident is on both sides, and the diagonal entrance angles are always equal.
The entrance angle is the entrance angle, and the contra angle increases when the entrance angle increases.
All objects reflect, specular reflection diffuses the reverse side.
3. Flat mirror imaging
The plane mirror is a virtual image with equal size and strong symmetry.
The distance from the object image to the mirror is equal, and their line is perpendicular to the mirror.
The drawing reflection is reversely extended, and the intersection of the dotted lines is the image point.
All image points form an image, and the virtual image should be represented by a virtual image.
4. refraction of light
Light enters another from one thing, and it is reflected and refracted at the same time.
The diagonal line enters the water to be refracted, and the broken line is close to the normal line.
The normal line is perpendicular to the interface, and the broken line is divided into two sides.
The light in the water enters the air obliquely, and the broken line is far away from the normal.
The trees become taller when viewed underwater, and the fishes become shallower when viewed on the shore.
The human eye perceives the light as a straight line and sees the object as a virtual image.
5. Dispersion of light
Red, orange, yellow, green, blue, indigo, purple, white light dispersion, seven-color light.
Shade three original red, green and blue, pigment three original red, blue and yellow.
Red objects reflect red light, and all other colored lights absorb.
No reflected light enters the eye, I see a piece of black.
All colored lights are reflected, rendering the object white.
All colored light is fully absorbed, and it is an object that appears black.
All colors of light can pass through, and the object is colorless and transparent.
6. Invisible light
The infrared light outside the red light, the higher the temperature, the stronger the radiation.
Use infrared night vision devices, and remote controls are often used.
Ultraviolet rays outside the violet light help the body to synthesize D (vitamin).
Ultraviolet rays kill microorganisms and also make fluorescent substances glow.
Lens and its application
1. lens
Speaking of the lens, it can transmit light; the middle is thick, the convex lens; the middle is thin, the concave lens.
Convergent action convex lens, divergent action concave lens.
The flat light converges to a point, which is represented by the focal point F.
The focal point reaches the optical center of the mirror, and the distance is called the focal length of the mirror (denoted by f).
2. Lens in life
The object is far and close to the camera, and the real image is reduced and inverted.
The object is close to the far projector, magnifies the real image and stands upside down.
A magnifying glass on the same side of the object, magnifying a virtual image upright.
The real image is upside down and the virtual image is positive, while the real image is on different sides and the virtual image is the same.
3. Convex lens imaging law and application
The object is imaged at twice the focal length and between one and two times (focal) distance.
The real image is upside down and zoomed out. This example is used in a camera.
Objects move closer, images move away, and at the same time the images grow bigger.
The object is imaged between one and two times the distance and outside the two times the focal length.
The real image is upside down and enlarged. This example is used in a projector.
The object is in the focus, and the moving light screen is not visible.
Look at the object through the lens and magnify a virtual image upright.
The object is on the same side as the image. This example is used in a magnifying glass.
The near image of the object becomes larger and the near image becomes smaller.
The double focal length is divided into size, and the double focal length is divided into virtual and real.
explain:
When the object is outside the focal length of the convex lens, the convex lens becomes a real image. Within one focal length, "u<f".
When the object is outside the double focal length of the convex lens (u>2f), the convex lens becomes a reduced real image.
When 2f>u>f, it becomes an enlarged real image. The virtual and real images that are not reduced are inverted, and the virtual images that are not inverted.
4. Eyes and glasses
The lens of myopia is thick, and it is difficult to see the distance clearly.
Before the high beam imaging the retina, wear a concave lens to return to normal.
In hyperopic eyes, the lens is thin, and it is difficult to see near and far.
The low-beam imaging retina is thick, wear a convex lens to adjust the light.
The eyes are 10cm near the point, and the photopic distance is 25cm.
Physical change
1. thermometer
A thermometer that measures temperature has a law of thermal expansion and contraction.
Mix ice water to make zero degree, standard boiling water Baidu meter.
2. Use of thermometer
The bubble is fully immersed in the test liquid without touching the bottom or wall of the container.
Enter and wait for a while, and then read the reading after the indicator stabilizes.
Counting still leaves the tested liquid, and the line of sight is level with the top of the column.
Readings: The upper reading is too small and the lower one is bigger.
3. Melting and solidification
When a solid state becomes a liquid, it means melting, and a liquid state becomes a solid state.
The solid is divided into crystals and amorphous, and amorphous melting is unlimited.
The crystal melts with a melting point, and the temperature does not change when it absorbs heat.
4. Vaporization and liquefaction
Vaporization
Liquid change to gas is called vaporization, including boiling and evaporation.
Evaporation occurs on the surface of the liquid at any temperature.
The liquid evaporates to absorb heat, and the temperature of the attached object drops.
Vigorous vaporization is boiling, and the internal surface is the same.
It occurs at a certain temperature, and the boiling endothermic temperature (degrees) does not change.
The boiling temperature is called the boiling point, and different liquids have different boiling points.
The pressure is related to it, and the boiling point (drop) is lower when the pressure decreases.
liquefaction
The gaseous transformation is called liquefaction, and there are two methods of liquefaction.
It can be liquefied by lowering the temperature, and the volume can also be compressed.
The phenomenon of liquefaction must be exothermic, and fog, dew, and white gas are liquefied.
5. Sublimation and sublimation
Solid state transformation is sublimation, gas state transformation is sublimation.
Sublimation endothermic sublimation release, camphor becomes smaller due to sublimation.
Violet iodine will sublimate with slight heat, condensing snow cream and mist.
Current and circuit
1. Charge
There are two types of triboelectricity: electric charge and electric charge.
Fur rubber rubber belt is negative, silk glass glass belt is positive.
The same kind of charge repels, and the different kind of charges attract.
Seeing the phenomenon of repulsion, the electrical charge must be the same.
Elementary charge: charge 1.6, multiplied by 10 to 19 squares.
2. Current direction
There are regulations for the formation of electric currents, and the directional movement of charges.
The direction of positive electricity movement specifies the direction of current.
Metal conducts electricity by (free) electrons, and the direction of electrons is reversed.
3. Series and parallel
Series circuit
The end-to-end connection is a series connection, and the series circuit is one way.
One switch controls all, but the position is different and the control is the same.
All electrical appliances affect each other (phase), and one stop will stop.
Parallel circuit
Connect the head to the head and the tail to the end, and the two points in parallel are parallel.
The electrical appliances can work independently without affecting each other.
Several circuits are connected in parallel, and the total control is controlled by all branches.
4. According to the actual picture circuit diagram
Look for wiring multi-line posts, and the relationship between series and parallel must be distinguished.
Draw branch circuits and two in parallel, then draw trunk circuits and power supplies.
Component symbols must be clear, and the corresponding must be checked after drawing.
5. Connect the physical diagram according to the circuit diagram
Pay attention to the connection according to the figure, one branch and two parallel connections.
Connect the main circuit and power supply three times, and add a voltmeter four times.
6. Design circuit
Design the circuit diagram first, the switch position is the key.
The switch controls who to string with, and the light is usually turned on.
All electrical appliances are controlled, and the switch must be on the main circuit.
After any switch is closed, the bell will ring on the main road.
7. Current strength
Ammeter
Ammeter, measuring current, measuring whose current is with whom.
"+" enters "-" exits and turns right, and the left turn line post is fixed and connected reversely.
It is forbidden to connect to the power supply directly, and the ammeter will be destroyed by short circuit.
The reading first looks at the range and then at the minimum scale value.
The range selects 0.6A, 0.02A one small grid.
The range is 3 amperes, and one small division is 0.1A.
8. Explore the current law of series and parallel circuits
The relationship between series currents, the currents are equal everywhere, I=I1=I2.
The characteristic of parallel current, the total current is equal to the sum of the tributaries, I=I1+I2.
Voltage, resistance
1. Voltmeter
Voltmeter, measure voltage, V in the circuit symbol circle.
Measure the voltage and parallel (connect) with whom, "+" in and "-" out, do not connect reversely.
Usually draw the circuit first, and add the voltmeter last.
The measuring range is 3V, 0.1V and one small grid.
The range is 15V, and one small division is 0.5 (V).
2. Explore the voltage law of series and parallel circuits
The relationship of the series voltage, the total voltage is equal to the sum of the partial pressures, U=U1+U2.
The characteristic of parallel voltage, the branch voltage is equal to the power supply voltage, U1=U2=U.
3. resistance
Conductor resistance is called resistance, and the symbol of resistance is R.
The unit of resistance is ohm, and the ohm symbol is Ω.
Three factors determine resistance, length, material, and cross-section (product).
Not proportional to voltage, current has nothing to do with it.
Affected is the temperature, which is usually not considered in the calculation.
4. rheostat
Sliding rheostat
Use a sliding rheostat to change the current string with whom.
Once the connection line is up and down, the key is to watch the connection offline.
The resistance of left connection and right shift becomes larger, and the resistance of right connection becomes smaller.
Ohm's Law
1. Ohm's law and its application
Ohm's law says that for current, I equals U to divide by R.
Correspondence of the three should be unified, the same conductor is the same route.
U equals I to multiply R, R equals U to divide by I.
2. Series and parallel resistors
The resistance in series should be larger, the total resistance is equal to the sum of partial resistance, R=R1+R2.
The resistance in parallel should be reduced, and the sub-resistance should be reversed and the sum is reversed, 1/R=1/R1+1/R2.
3. Measuring the resistance of small bulbs
To measure the resistance of a small bulb, the principle is R and U divided by I.
Need volt-ampere meter, bulb sliding rheostat.
The connection switch should be disconnected and the resistance value adjusted to the maximum before closing.
Series circuit formula
In the relationship of the series circuit, the currents in all parts are equal.
The total pressure is equal to the sum of partial pressures, and the total resistance is equal to the sum of partial resistances.
4. Parallel circuit formula
In the relationship of parallel circuits, the total current is equal to the sum of the tributaries.
The support voltage is equal to the power supply voltage.
Electric power
1. Electricity measurement
The unit of electrical energy is joule (J), which is commonly used in daily life (KWh).
The electric energy meter measures the power consumption, and the power consumption is equal to the count difference.
1 degree=1KWh=3.6×106J
600r/KWh said
Every kilowatt-hour is consumed. The turntable rotates 600 times.
The turntable rotates n times, and the power consumption is n/600KWh.
2. Electric power
The speed of power consumption is represented by P.
The electrical energy consumed within 1 second is called the electrical power of this electrical appliance.
Electric energy equal to P is divided by time P=u/t, and voltage and current are multiplied by P=UI.
The unit of power is watt, 1 (W) and 1 volt ampere, 1W=1VA.
Given that p and t are used for energy consumption, W is equal to p times t.
3. Electric power calculation
Lights and electrical appliances are marked, rated voltage (U0) and power (P0).
Normal lighting current, I equals P0 divided by U0. I=P0/U0.
The voltage changes and the power changes, where the resistance is unchanged.
When encountering electrical appliances to find resistance, R and U2 divided by P, R=U2/P.
4. Joule's Law
Joule's law says that three factors are related to heat.
The square of the current is the key, multiplied by resistance and time.
The unit of heat is Joule, which is commonly used for energy loss.
5. fuse
Lead-antimony alloy fuse, high resistance and low melting point.
If the wire is too thick, it is not safe, and the circuit is often cut off if it is too thin.
Choose the right fuse, don't use iron copper wire.
6．
Live wire L, neutral wire N, metal shell grounded E.
The neutral wire is grounded and there is electricity, the neon gas is a live wire, and the neon tube has a resistance of one million.
Press the tip of the pen card to connect the wires, making sure not to touch the tip with your fingers.
In the event of an electric shock, the power is cut off first, and the insulating rod is used to pick up the line.
Electricity and Magnetism
1. Magnetic phenomenon
Both ends of the magnet are extremely strong, and the guide S points to north N.
Different names attract the same name row (repulsion), and common magnets rely on magnetization.
2. magnetic field
The direction of the magnetic field is specified, and the magnetic needle is stationary and the north pole is pointed.
The magnetic line of induction outside the magnet, starting from the north pole (N) back to the south pole (S).
Shen Kuo discovered the magnetic declination of the geomagnetic field around the earth.
3. Electromagnetic
There is a magnetic field around the current, which proves that Oersted, Denmark.
The magnetic pole of the energized solenoid is judged, and the right hand is stretched out under the ampere law.
The four fingers walk along the current and the direction of rotation cannot be reversed.
The thumb refers to the N pole, and the palm cut is marked S.
4. Electromagnet
The magnetic strength of the solenoid is fixed, and the current turns are inserted into the iron core.
A solenoid with an iron core is usually called an electromagnet.
The switch controls the presence of magnetism, and the current controls the magnetism strength.
5. Electric motor
In the magnetic field of the energized coil, the force will rotate.
The stator does not move the rotor and continues to rotate the commutator.
Convenient control and high efficiency, electrical energy is converted into mechanical energy.
6. Magnetism
Electromagnetic induction Faraday, magnetism generates electricity to close the circuit.
Part of the conductor cuts the magnetic wire, and there is in the induced current wire.
Change the direction of alternating current, and mechanical energy turns into electrical energy.