Physics magnetism in the second year of junior high school, physics and magnetism knowledge points i

Point south. Because the earth is a large magnet, its two magnetic poles are close to the two poles of the earth, and under the action of the geomagnetic force, the magnetic needle is drawn to the north-south direction. We know that the magnetic poles of the different names are attractable, and the s pole of the geomagnetism is at the north end and the n pole is at the south end, so the n pole of the magnetic needle is always pointing to the north and the S pole is always pointing to the south.

The magnetic poles of the magnetic needle and the magnetic poles of the Earth are not in contact, but they are attracted to each other, indicating that there is something invisible around the magnet, which is called a "magnetic field". The presence of the Earth's magnetic field is the reason why the magnetic needle is able to indicate north and south.

The earliest compass in the world is the "Sinan" made during the Warring States period in China. It is made by grinding a natural magnet into the shape of a spoon, with the handle of the spoon being the pole, so that the center of gravity falls in the center of the round and smooth spoon head, and then the spoon is placed on a smooth plate. To use, lay the head flat and turn it by turning the handle with your hands.

When Sinan stopped, its long handle pointed south. At that time, some people went to the mountains to pick jade, and they were afraid of losing their way, so they brought their boss Nan to discern the direction.

Sinan is the compass, and its long handle points to the south, then the long handle is the S pole (South Pole), and the spoon head is the N pole (North Pole).

If it is a guide to the spoon handle, it means that the spoon handle is the S pole, the S pole, and the definition of the S pole is the south pole, which is called the S pole.

S pole. Because the north pole of geography is the south pole of geomagnetism.

Magnet 1Magnetism: The property that can attract iron, cobalt, nickel and other substances.

2.Magnet: An object that has magnetic properties.

3.Pole: The part of the magnet that is most magnetic.

N pole and S pole.

In the experiment, a small magnetic needle was placed on the tip of the needle, and the small magnetic needle was tossed by hand to observe the pointing when it was stationary.

Note: 1. Do not let the magnet get close to it.

2. Observe the pointing of other students' small magnetic needles.

The position of the small magnetic needle when stationary is always pointing north-south.

The end of the small magnetic needle pointing north is called the North Pole (N-pole).

The end pointing south is called the South Pole (S pole).

4.The law of interaction between magnetic poles:

The poles of the same name repel each other, and the poles of the same name attract each other.

Magnetization experiments. 5.Magnetization: The process by which an object that was not originally magnetically magnetic.

If the magnetized object is an iron rod, the acquired magnetism will disappear immediately, and if the magnetized object is a steel rod, the acquired magnetism will remain for a longer time in the magnetized way:

a. Touching or approaching the magnet;

b. Use one pole of the magnet to rub in the same direction many times.

1.Electromagnetism is the magnetic effect of the current, that is, there is a magnetic field around the current, and the direction of the magnetic field of the current is related to the direction of the current. (The Oster experiment in the books).

It is precisely because there is a magnetic field around the current that the energized conductor is like a magnet that has a magnetic force on the magnet placed in it, which is the effect of the magnetic field on the electric current, and it is also the principle of the motor. (Because the motor consumes electrical energy, there is a power supply in the schematic diagram of the motor, and the generator wants to generate electrical energy, so there is no power supply in the schematic diagram is an electrical appliance or ammeter).

2.Magnetism is the phenomenon of electromagnetic induction: when a part of a conductor in a closed circuit moves in a magnetic field to cut magnetic inductance lines, an electric current is generated in the circuit. That is, the generator principle.

3.A microphone and earpiece are similar to generators and motors, respectively. (Microphones and generators convert mechanical energy into electrical energy, and earpieces and electric motors convert electrical energy into mechanical energy).

Electromagnetism is the magnetic effect of an electric current, which means that there is a magnetic field around the electric current. Magnetogenesis is a phenomenon of electromagnetic induction. The principle of an electric motor is that an energized conductor is subjected to a force in a magnetic field.

The principle of the generator is the phenomenon of electromagnetic induction, that is, when a part of the conductor of a closed circuit moves in a magnetic field to cut the magnetic inductance line, an induced current will be generated in the circuit.

Two methods:

1. Use the directivity of the magnet.

Hang the measured magnet and see where it points at both ends when it is stationary, the end that points to the geographic north pole is the north pole, and the end that points to the geographic south pole is the south pole.

2. According to the law of interaction between magnetic poles.

Use the north pole of a magnet of known polarity to approach one end of the magnet to be measured, and if they are attracted to each other, then the end of the magnet to be measured is the south pole; If they repel each other, then this end of the measured magnet is the North Pole.

Question 1: Balance balance.

In the process of A being sucked up by B, the whole force change is in one system. The mutual attraction of AB, the pressure of the bracket on the pallet, and the supporting force of the tray on the support of the bracket balance each other. So the balance is balanced.

Question 2: Imbalance.

The moment the left disc A is sucked up by B, the pressure of A on the tray decreases, and the reduced part of the force is balanced with the pull of the person on B, but the pull of the person on B is not in this system, so the balance is unbalanced.

Question 3: Can move and cannot move in a straight line at a uniform speed.

The car where A is subjected to the magnetic force of B will move towards B, if the force of A is F, because F will increase with the decrease of AB distance, so A will not do uniform linear motion. In junior high school physics questions, the relationship between magnetism and distance should not be considered. Therefore, the trolley should do uniform acceleration linear motion.

The main thing is to clarify the force system to be analyzed. It's not that hard.

1.The scales will still be balanced. Because when magnet B attracts magnet A, the suction force between the two magnets is equal (meaning that when magnets A and B attract, the upward force of A and the downward force of B are equal - interaction), although magnet A lifts off, the downward force of magnet B on the bracket becomes larger, so the balance can continue to be balanced.

2.That's when the scales are out of balance. At the moment when magnet A is about to be sucked up, the pressure on the balance is 0 (if the balance is an iron disk), and at this time, another magnet is in the hand, which means that the left disk has nothing at this time.

3.If there is no friction on the floor, the car will move forward (if the friction is large, the car may not be able to move), but it will not be straight at a uniform speed, because the front is always attracted by another magnet B, which is equivalent to a force that will always produce an acceleration (this thing is said in high school), and the speed will always increase.

These 3 questions all belong to the problem of magnetic attraction, and it is necessary to judge (o) by looking at the object of suction and the effect on the object. Hopefully one will be adopted.

1.Equilibrium Because the mutual attraction of the magnets in the left disc is an internal force for the entire left disc and has nothing to do with the suction at this time.

2.Unbalance When magnet B is close, the force of magnet A on the pallet is the difference between the gravity of the magnet itself and the suction force between magnets A and B, so the balance is unbalanced.

3.It will move but not in a uniform linear motion, because in the process of moving, the distance between the magnets A and B is getting smaller and smaller, and the magnetic force is inversely proportional to the distance, and the pulling force acting on the trolley is getting bigger and bigger, and the trolley is moving in a linear motion with variable acceleration.

See whether it is an internal or external force and whether there is a change in the force.

Two. 1.The sound emitted by the radio means that the circuit is connected, and the failure to make sound means that the circuit is broken, and the bridge is an electromagnetic wave.

2.Oscillation circuitsElectromagnetic oscillations produce electromagnetic waves.

3. 1. The propagation of sound requires a medium.

2. The propagation of electromagnetic waves does not require a medium.

3. Light waves are electromagnetic waves.

Frequency f period t wave Zheng closed long shout annihilation wave velocity v= t= f=3x10 8

Four. 1.Television, radar, radio communications, photography, medical care...

2. Electromagnetic radiation causes injury and genetic mutation.

Magnetism 1 Magnets and poles [poles of the same name repel each other, poles of different names attract each other] The property of an object that can attract iron, cobalt, nickel and other substances is called magnetism. A material that is magnetic is called a magnet. The poles of a magnet always come in pairs.

2 Magnetic field: There is an area in the space around the magnet that acts on other magnets.

The basic property of a magnetic field is the effect of a magnetic force on the magnet placed in it.

Direction of magnetic field: When the small magnetic needle is stationary, the direction pointed to by the n pole is the direction of the magnetic field at that point. The magnetic field around the magnet is represented by magnetic inductance lines.

The geomagnetic north pole is near the geographic south pole, and the geomagnetic south pole is near the geographic north pole.

3 Magnetic field of electric current: Oersted's experiment shows that there is a magnetic field around the electric current.

An energized solenoid is externally equivalent to a bar magnet.

The relationship between the direction of the current in the energized solenoid and the polarity at both ends of the solenoid can be determined by the right-hand spiral rule.

Dude, what kind of question are you asking? , is it specific?