Physics magnets in junior high school, and a summary of the knowledge points of physics electromagne

The Earth is a big magnet with the N-pole near the South Pole and the S pole near the North Pole.

When the plane flies over the South Pole, the N pole of the earth is below the plane, the magnetic poles of the same name attract each other, and the magnetic poles of the different names repel each other, so the N pole of the small magnetic needle is repelled and points to the sky, and the S pole is attracted by the N pole of the earth and points to the ground.

It's the same when flying over the North Pole.

Note that the geomagnetic south pole (s) is near the geographic north pole and the magnetic north pole (n) is near the geographic south pole and is reversed.

Because the Earth is a huge magnet, and we are in other places, the n of the compass always points to the North Pole of the Earth (in Prince Edward Island, Canada), and because the North Pole of the Earth is on our north side, most of the time the North Pole points north.

When your plane flies over the North Pole, the Earth's North Magnetic Pole is just below your plane, so the compass is n-magnitude down.

The geographic south pole is the magnetic north pole.

So near the South Pole, the n-pole of the small magnet points vertically towards the sky.

And nearby, because the geographical south pole is the magnetic north pole and does not exactly coincide.

The direction of the n pole of the small magnetic needle is the direction of the magnetic inductance line, and the magnetic inductance line in the magnetic field on the earth's surface points from the south pole to the north pole.

This should be the content of high school.

Because the magnetic inductance lines of the earth are emitted from near the south pole of the earth and from near the north pole of the earth.

That is, the geomagnetic north and south poles and the earth's north and south poles are reversed!!

The direction of the magnetic inductance line is from the n pole back to the s pole, you can think of the earth as a big magnet, and then think about the ns pole of the compass along its magnetic inductance line.

Oersted's experiment shows that energized wires, like magnets, have a magnetic field around them; The direction of the magnetic field of the current is related to the direction of the current.

Then the energized solenoid should also have a magnetic field, and the experiment shows that the magnetic field outside the energized solenoid is the same as the magnetic field of the bar magnet, and the two ends of the energized solenoid are equivalent to the two poles of the bar magnet. When judging the magnetic pole of the energized solenoid, use the right-hand spiral rule: judge the spiral with amps, and hold the solenoid tightly with the right hand.

The direction of the current is four fingers, and the n pole is pointed to the tip of the thumb.

The working principle and application of the electromagnet: the solenoid is tightly sleeved on an iron core, which constitutes an electromagnet.

Factors affecting the magnetic strength of the electromagnet: The electromagnet is magnetic when it is energized, and it is not magnetic when it is powered off; The greater the current through the electromagnet, the stronger its magnetism; When the current is constant, the more turns of the coil of the solenoid with the same shape, the stronger its magnetism.

Electromagnetic relay: The structure of the electromagnetic relay is shown in the figure, and its basic components include electromagnet (a), armature (b), spring (c), and moving contact (d). The electromagnetic relay is based on the advantages of the electromagnet, and the current can be controlled to work with the magnetism of the electromagnet.

The working principle of the electromagnetic relay is to control the current through the electromagnet to achieve the purpose of controlling the working circuit. Therefore, the general relay circuit consists of two parts: a (low-voltage) control circuit and a (high-voltage) working circuit. Relay circuits can be used for long-distance operation and automatic control.

Common test methods. This knowledge is often examined in the form of multiple-choice questions and fill-in-the-blank questions, the magnetic pole of the electromagnet, the influencing factors of the magnetic magnitude of the electromagnet, the working principle and application of the electromagnetic relay, and the right-hand spiral rule is examined in the form of drawing questions.

Typical example] Example analysis: The attached drawing is a schematic diagram of a flood control alarm. K is the contact switch, and B is a funnel-shaped bamboo cylinder with a float inside. Let's explain how this kind of alarm works.

Analysis: Some electromagnetic relays have a wide range of uses. When analyzing the working principle of various application circuits, it is mainly necessary to understand the on-off situation of the contact when the electromagnet is on and off, and its effect on the circuit.

Answer: When the water level rises, float A will push B to rise together, and when the water level reaches or exceeds the warning line, the control circuit is turned on. At this time, the current passes through the electromagnet, causing it to attract the armature, and the working circuit is turned on, and the electric light glows for alarm.

When the water level drops, float A drives B down together. When the water level is lower than the warning line, the control circuit is disconnected, and the electromagnet stops working because there is no current passing through, and no longer attracts the armature, so that the working circuit is disconnected, and the electric light no longer emits light alarm.

Magnetism: The property of an object to attract substances such as iron, cobalt, nickel, etc.

Magnets: Objects that have magnetic properties are called magnets. It is directive: it means that the suspended magnet points to the north and south after it is stationary.

The basic property of the magnetic field: it has a strong effect on the magnet placed in it, and the magnetic inductance lines outside the magnet always point from the north pole to the south pole. The direction of the tangent of the magnetic inductance line is the direction of the magnetic field at that point;

The tangent direction of a point in the magnetic field, the direction of the magnetic field, and the direction of the North Pole when the small magnetic needle is at rest are the same.

1, Iron, Cobalt, Nickel;2. After the hanging, the guide is in the north direction;3. It has a strong effect on the magnet put into it; 4.The North Pole points to the South Pole tangent; 5. Tangent magnetic field of the North Pole.

The tangent of a circle is perpendicular to the radius of its tangent point; A straight line that passes through the non-centered end of the radius and is perpendicular to that radius is a tangent of the circle (this is mathematics).

1.Magnets have the property of attracting substances such as iron, cobalt, nickel, etc., which we call magnetism2The magnet has the directivity of a guide north.

3.The basic properties of the magnetic field: (It has a magnetic effect on the magnet placed in it, and we often use the small magnetic needle to check whether there is a magnetic field in the space where the small magnetic needle is located.) ）

4.(1) The magnetic inductance line always closes the curve, which comes out from the n pole on the outside of the magnet and enters the s pole, and returns from the s pole back to the n pole on the inside, forming a closed curve. (2) The direction of the magnetic inductance line is the direction of the force on the north pole of the small magnetic needle at this point.

5.Tangent magnetic field of the North Pole.

Put a wire thick enough around the microwave oven (in order to be able to absorb enough electromagnetic waves), and connect an ammeter in the wire (to be sensitive, choose a small range), and see if the ammeter has an indication if there is microwave leakage on the surface (microwaves will cause current in the conductor).

Just put on a semiconductor radio and see if there is any interference.

Use a semiconductor radio to get close to the microwave oven around the door and listen to see if there is a reaction

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?

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.

1.Universal: From N-level to S-class (innumerable).

The NN type also starts from the N-level and makes an arc outward. Type SS The scissor head is pointed towards the S class. The magnetic field distribution of the NS type is from the n order back to the S pole.

In short, it is correct to follow the path of starting from the n pole and returning to the S level.

2.The second problem should be explained simply as the phenomenon of polarization. The charged body polarizes the small and light objects and uses the attraction between the charges to suck up the small and light objects.

3.The ability of each atom to bind electrons is different, and when an atom with a strong ability to bind an electron meets an atom with a weak ability, the stronger side will attract the weaker atom. Thus one gains electrons and the other loses electrons.

The party that gains the electron is negatively charged, and the party that loses the electron is positively charged.

Being charged only with a positive or negative charge is also considered electrified.

When there are two charges at the same time, if the positive and negative charges are equal in number, the phenomenon of neutralization (i.e., inelectrified, i.e., uncharged) will occur; If one of the charges is more numerically than the other, it is also electrically charged.

4.The electroscope itself is not electrified. Under the action of gravity, the metal sheet will naturally close, and only when it comes into contact with a charged body, whether positive or negative, the metal sheet will open. So take advantage of this principle.

5.Fundamentally the question you're asking doesn't exist at all, because heterogeneous charges attract each other, so there's no question of repulsion.

If there is a question that you don't understand, you can continue to ask.

Uh, I'm sweating!! Actually, the questions you ask are quite simple, but if you want to answer, it is more troublesome. Because I have to draw a picture or something. Therefore, it is recommended that you call the teacher directly or ask your classmates.

The shape of the s-s is like two lobsters looking at each other's whiskers is the distribution of magnetic inductance lines, and the distribution of n-s magnetic inductance lines is like a broken thread, and it is like the surface texture of a basketball.

2.The energy of a dotted object is that the surface of a small object generates an induced charge, and the opposite charge attracts.

3.Charging means that there are more positive charges than negative charges on an object, or more negative charges than positive charges (including bound charges).

4.The electroscope is not charged in this province, but the two metal foils are connected together, so when a charged object touches the upper end of the ball, the two metal foils have the same charge and are repulsed.

5 Positively charged and negatively charged objects are attracted to each other, like a handsome guy meets a hot girl.

1.The magnetic inductance lines come out from the n pole on the outside of the magnet and return to the s pole, the n-n type and the s-s type both diverge outward, the difference is that the former arrow points outward, the latter arrow points inward, and the n-s type is a closed curve, and the arrow points from n to s. 2.