candidates are expected to have a thorough understanding of the syllabus details outlined in the accompanying figure properties of magnets magnets have two poles as a north and a south at the end of the magnets A magnetic forces are the strongest at north and south poles. When two magnets are held close together, there will be a force between the magnets. Unlike poles attract, like poles repel.
Magnetic materials. They will always be attracted to a magnet and can be magnetized. Magnetic materials contain iron, nickel or cobalt.
For example, steel is mainly iron. There are two types of the magnetic materials as hard magnetic materials such as steel are difficult to magnetize but do not readily lose their magnetism. They are used for permanent magnets. Soft magnetic materials such as iron are relatively easy to magnetize and easy to lose magnetism so their magnetism is only temporary.
They are used in the cores of electromagnet and transformers. because their magnetic effect can be switched on and off or reversed easily. Non-magnetic materials are not attracted or repelled by magnets and cannot be magnetized. They include all metals that do not contain iron, nickel or cobalt and all non-metals.
To determine whether a material is a magnet, a magnetic material, or a non-magnetic material, bring it close to a known magnet. If it can be repelled by the known magnet, then it is a magnet. If it can only be attracted and not repelled, then it is a magnetic material.
If it is not affected, then it is a non-magnetic material. For example, there are three unknown metal bars and a known magnet. When a north pole is brought near the end A, they attract each other. Then the north pole of a known magnet is brought near the end B, they attract each other again.
This shows that bar AB is a magnetic material. When a north pole is brought near the end C, they repel each other. This shows that bar CD is a magnet, and the end C is north pole, then the end D is south pole.
When a north pole is brought near the end E, so nothing is happening. This shows that bar EF is non-magnetic material. Magnetizing the magnetic materials. Magnetization is the process of inducing magnetism in magnetic materials.
There are three ways to magnetize the magnetism of a magnet. Induced magnetism of magnetic materials by a strongly magnet. The iron and steel can magnetized when placed near a magnet, but its magnetism is usually weak.
When a iron bar and a steel bar are brought to attract, with a north pole of a strong magnet. The iron and steel are magnetized. These ends of iron and steel are south poles and another end of both are north poles.
When the iron and steel are brought away from the north pole of the strong magnet, the iron loses its magnetism. The steel is still permanently magnetized. Magnetizing a magnetic material by stroking it with a magnet.
This method can be magnetized more strongly. A steel bar is stroked with the north pole of a magnet in one direction. This end of the steel bar is magnetized to be a south pole.
This end is magnetized to be a north pole. When a south pole is stroked along the steel bar in same direction, this end of steel is magnetized to be a north pole. And this end is magnetized to be a south pole. When a north pole is stroked along the steel bar in the opposite direction, this end of steel is magnetized to be a north pole, and this end is a south pole.
Magnetizing a magnetic material using direct current. This method is one of the most effective ways to magnetize a material. A steel nail is inserted into a long coil of wire. The DC power supply is turned on to pass a large direct current through the coil. To keep a steel nail inside a coil, the current generates a magnetic field that magnetizes the steel.
This end is magnetized to be North Pole. And this end is magnetized to be south pole. We will explain this process in more detail in the section of 4.5.3 Magnetic Effect of a Current.
Demagnetizing the Magnets. Demagnetization is the process that destroy the magnetism of a magnet. There are three ways to demagnetize the magnetism of a magnet. Demagnetization by heating. To place a magnet along the west-east of the earth.
This is because the earth is a magnet and its poles are along north-south. It is easy to demagnetize when a magnet is placed along west-east. To heat a magnet with a fire until it demagnetizes. Demagnetization by hitting. To place a magnet along the west-east of the earth.
To hit a magnet by a hammer. with a moderate amount of force until it demagnetizes. Demagnetization by alternating current.
To insert a magnet into a long coil, turn on the AC power supply. Slowly pull the magnet away from the coil until it is completely outside of the coil. The large alternating current generates the changing magnetic field to demagnetize the magnet.
Don't keep a magnet in the coil. because this cannot be demagnetized to complete. Magnetic field.
All magnets are surrounded by a magnetic field. The magnetic field is defined as the region in space where magnetic material experience a force. Magnetic field lines are imaginary lines that represent the direction and strength of a magnetic field.
Magnetic field lines run from the north pole to south pole. Magnetic field lines cannot cross each other. Strong magnetic field strength where lines are close each other.
And weak magnetic field strength where lines are far apart each other. The arrow is indicated the direction of force acting on the north pole of a magnet at that point. The magnetic field lines around a bar magnet. Magnetic field lines run from north to south.
Magnetic field lines are very close each other at the north and south. This shows that the magnetic field strength is strong. Magnetic field lines are far apart where further from the magnet.
This shows that the magnetic field strength is weak. The magnetic field lines pattern around two magnets with opposite poles. The magnetic field lines pattern around two magnets with same poles.
This is neutral point, which has no magnetic field strength and no magnetic force to act on the magnetic material. A uniform magnetic field between two opposite poles. Magnetic field lines run from north to south poles. Magnetic field lines are parallel and same space each other. This shows that the magnetic field strength remains constant.
The magnetic field lines around the earth. Inside the inner core contain the iron and nickel, which are the magnetic material. This causes the core of the earth is a magnet.
The north pole of earth is south pole of the magnet, and south pole of earth is north pole of the magnet. The magnetic field lines of the earth run from the south to north of the earth. A needle of the compass is always pointed to the north pole of the earth.
So, the needle is a magnet. And the arrow of the needle is north pole magnet. Which attracts to the south pole of earth's magnet. This shows that the needle of a compass will always point in the same direction of the magnetic field line.
Plotting the magnetic field lines around a bar magnet. Using iron fillings, place a piece of paper or glass on top of the magnet. Gently sprinkle iron fillings on top of the paper or glass.
Now carefully tap the paper or glass to allow the iron fillings to settle on the field lines. Using a compass, place a magnet on top of a piece of paper. Place a compass at the one end of the magnet.
Draw a dot at the tip of the needle. Then the compass is moved so that the needle lines up with the previous dot, and so on. When the dots are joined up, the result is a magnetic field line. More lines can be drawn by starting with the compass in different positions.
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