A few questions about the physics of the second year of junior high school, about the physics questi

Reflection of light. Reflection of light: The phenomenon of light changing the direction of propagation at the interface of two substances and returning to the original substance, is called the reflection of light. Understand the law of reflection of light.

Induction. 1 In the phenomenon of reflection, the reflected rays, the incident rays, and the normals are all in the same plane.

2. Reflected rays, incident rays are separated on both sides of the normal.

3 The angle of reflection is equal to the angle of incidence It can be summarized as: "three lines are coplanar, two lines are separated, and the two angles are equal" The reflection of light.

Refraction of light. When light travels from one medium to another or travels in the same inhomogeneous medium, the phenomenon of deflection of direction is called refraction of light.

1. The refracted rays and the incident rays are separated on both sides of the normal (the normal is centered).

2. The refracted ray, the incident ray, and the normal are in the same plane. (Three lines and one side).

3. When the light rays are obliquely emitted from the air into other media, the refractive angle of the angle is less than the angle of incidence;

4. When light rays are emitted into air from other media, the angle of refraction is greater than the angle of incidence.

The above two items are summarized as: who is faster and who is bigger. That is, in which material the light travels fast, then it is a larger angle regardless of whether it is the angle of refraction or the angle of incidence).

5. Under the same conditions, the larger the angle of incidence, the greater the angle of refraction.

Refraction: The light that passes through the medium has a certain deviation from the original direction of travel.

Reflection: Light on the surface of the medium is shot at a certain angle to other directions, and does not enter the medium.

Camera focal length, even the distance between the film and the lens.

The reflection of light refers to the physical phenomenon that the light rays are reflected to other places when they encounter obstacles in the same homogeneous medium, and they are divided into specular reflection and diffuse reflection.

Refraction, on the other hand, refers to the physical phenomenon in which light rays travel from one medium to another and the direction of propagation changes (for example, the direction of light rays in the air entering water will be deflected towards the normal).

The reflection of light is the refraction of light when it hits the surface of water, glass and many other objects, and when light is obliquely reflected from air into water or other mediums, the refraction is replaced by a deflection in the direction of the normal.

1. Refraction simply means that it can pass through an object. Reflections cannot penetrate objects. Grow the focal length.

Solid Lines are used for real images and dotted lines are used for virtual images.

The refraction of light refers to the phenomenon that light is deflected when it hits into a medium such as water, and the reflection is that it bounces back, and the following means that it is all forgotten.

Rainbow is a natural phenomenon caused by the reflection and refraction of light from sunlight into water droplets in the air.

We know that when sunlight passes through the prism, the direction of travel is deflected, and the original white light is broken down into bands of red, orange, yellow, green, blue, indigo, and violet. When it rains, or after rain, the air is filled with countless tiny droplets that can deflect the sun. When sunlight passes through water droplets, it not only changes the direction of travel, but is also decomposed into red, orange, yellow, green, blue, indigo, violet and other colors.

If the angle is right, it becomes the rainbow we see.

Gravity, vertically downward, x10 4n

Support force, vertical upward, x10 4n

Resistance, horizontal to the west, 5

x10^3n

Traction, horizontal to east, 5

x10^3n

1、b.Both A and B are positively charged (because triboelectric is one object that loses electrons and becomes positively charged, and another object gains electrons that become negatively charged, it is impossible for both to be positive).

2、b.Mutual repulsion (rubbing the fur against the rubber rod, after rubbing, the rubber rod is negatively charged while the fur is positively charged; The glass rod rubbed by silk is also positively charged, so the fur is repelled when it is close to the glass rod).

3. There is both a positive charge and a negative charge on the glass rod, when the silk rubs the glass rod, the glass rod is easy to lose electrons (electrons are negatively charged), and the negative charge is less than the glass rod shows a positive charge, and at the same time, the silk gets negatively charged electrons from the glass rod, so its negative charge increases, so the silk shows a negative charge. In short, triboelectric charging is not caused by the generation of electric charges, but by the transfer of electric charges between objects rubbing against each other.

There are 3 possibilities for this question, 1 A and B did not give electrons to each other, nor did they lose electrons, (electrons are negatively charged,) so they are not charged.

2 A loses electrons, and A, who originally had an equal amount of positive and negative charge, has a positive charge because he loses his negatively charged electrons, and B has a negative charge because he gains electrons. 3 means that A gains electrons and B loses electrons.

b The rubber rod rubbed against the fur has a negative charge, then the fur belt rubbed against the rubber rod has a positive charge, and the silk rubbed glass rod has a positive charge, so the same charge repels each other.

Question 1 A Triboelectric Electrification Question 2 A Heterogeneous charges attract each other Atoms are composed of nuclei and electrons, electrons (negatively charged) move outside the nucleus (positively charged), different atoms have different electrons, and some electrons in the same atom are close to the nucleus and some are far away from the nucleus. You are only in the second year of junior high school can understand the loss of electrons in this way, because the electrons are negatively attracted to the nucleus, the nucleus attracts the electrons of other atoms to gain electrons, and the electrons of the atom are attracted away by other nuclei to lose electrons.

, you can use the method of elimination, first of all, a can be obtained by common sense, for example, if you take two books and rub them, you will not be electrified; If you choose one of the CDs, then the other one should also be selected, but because it is a single choice, you can't choose both, so the CDs are all wrong, so choose B.

However, it can be seen from the common sense of physics that if an object appears to be positively charged, its electrons move to another object, making it negatively charged, and it is impossible for two objects to have the same kind of charge after friction;

Since the fur belt is negatively charged and the glass rod is positively charged, they should be attracted to each other3This memory is not too clear, it has to do with the transfer of electrons. And there are no shortcuts, you only have to meet one and remember one.

b b When the silk rubs the glass rod, because the silk has a strong ability to bind the electrons, the electrons on the glass rod are transferred to the silk, so it is positively charged.

The essence of the dotted object is the transfer of electrons. Either one loses electrons, one electrons, or both objects lose electrons at all. It is impossible for both objects to lose electrons, that is, to be positively charged.

The fur belt that has been rubbed against the rubber rod is positively charged, and the silk rubbed glass rod is positively charged. The same kind of charge repells each other.

b The friction of two objects is the process of seizing electrons from each other, that is, the relationship between being deprived of electrons (now positively charged) and seizing electrons (now negatively charged), and the two objects may have the same binding force on electrons by atomic nuclei, so they cannot take each other's electrons from each other, and they are not charged; And when the nucleus of A has a stronger binding force on electrons than B, A is negatively charged, and vice versa.

The second course, a textbook foundation, how to learn.

3. If the binding force of A's nucleus to the electron is stronger than B's nucleus, A will take electrons from B, and the electrons are now negatively charged, and if there is more, it is negatively charged, on the contrary, B loses electrons, and the charged characteristics of the nucleus are manifested, and it is positively charged (the nucleus is positively charged, and the electrons are negatively charged).

3. The specific characteristics of which two materials are positive and which are negatively charged after rubbing against each other is determined by the properties of the materials, and the level of the second year of junior high school cannot be understood.

1.In the case of parallel connection, the current of each resistor is added up to the supply current.

In series, the current is equal everywhere. If you want to measure, just connect those resistors in series in the circuit, and then put the ammeter string circuit, but the current will change with the different resistances, I don't know what the nature of your problem is.

2. (1) (2) (The first and second questions need to be combined).

After the voltmeter is connected to both ends of the power supply, it is natural to measure the power supply voltage, after intervening in a resistor, then it is a series circuit, and the series circuit has a voltage dividing effect, but because there is only one resistance, the voltage is all divided to this resistor, and the sum of the voltages at both ends of each resistance in the series circuit is the total voltage, that is, the power supply voltage, the power supply voltage is forever constant, and it will only distribute the voltage to the resistor.

For example, a power supply voltage of 6 volts is connected in series with two resistors, one of which is divided into 2 volts and the other is divided into 4 volts, and 2 volts plus 4 volts is 6 volts, that is, the supply voltage.

In this problem, the supply voltage is volts, and the supply voltage allocates all the voltages to a resistor, because there is only one resistor to divide. Therefore, the voltmeter book connected to both ends of the power supply is the supply voltage, and the voltmeter book connected to the resistor at both ends is the voltage of the resistor, and the two voltages are equal.

3. To measure the fixed value resistance voltage, as long as the voltmeter is connected to both ends of the resistance. But what is this topic, is it for you to calculate the resistance voltage, why do you want to measure it, it doesn't make sense to measure it.

Your first question and the third question of the second question are not very clear, so it is recommended that you make the question clearer.

1. Connect with a sliding rheostat, power supply, ammeter and voltmeter, and the voltmeter and resistor are connected in parallel. Then change the sliding rheostat to change the resistance value, and then record the voltage and the indication of the circuit table, and turn it into a volt-ampere characteristic curve, then the intersection point with the voltage axis is the electromotive force, and the intersection point with the current axis is the current of the power supply.

2. (1) Power supply.

2) Because this is related to the principle of the voltmeter, there is a resistance inside the voltmeter, and the resistance value is very large, so the fixed value resistance is very small relative to him, so the indication is unchanged.

3) Just connect the voltmeter in parallel with the resistor.

It can only be said that the fixed value resistance is too small, which is similar to the internal resistance of the power supply. The voltage of the external circuit is measured; The ammeter can be connected internally, and the voltage can be connected to the beginning of the resistor and the end of the ammeter. Calculated with r=u i.

1.How to measure the current of the power supply.

Connect the ammeter in series into the circuit, remembering to thread a resistor at the same time (using the series circuit to have equal currents everywhere).

1) Power supply voltage.

2) Because it is a parallel connection (in the parallel circuit, the voltage of each part of the branch is equal and equal to the power supply voltage).

3) Using the derived formula U=IR of Ohm's law, the current of the resistor passing through the resistor is measured first, and then multiplied by its resistance value, the voltage at both ends of the resistor can be obtained (the resistor voltage is wrong, it should be the voltage at both ends of the resistor).

1.The current of the power supply can be measured by the method of trial touch (one end of the electricity is in contact with the power supply and the other is in contact with the power supply for a short time), and the ammeter index can be roughly seen. 2.

In parallel circuits, the voltage indication is the same), this circuit should be the voltage of the power supply, and it should also be the voltage of the resistor.

In series with the circuit under test of the power supply because the resistance and voltage are not related to the conclusion is obtained.

Solid brick volume v = 20 15 10 = 3000 cubic meters. Hollow brick volume = v 60 = 1800 cubic meters. Density = mass Volume = cubic meters =

The quality of solid bricks.

6 (20*10*15) = density.

Average density of hollow bricks: 3600 20*15*10=

Density of solid parts of hollow bricks.