PHYSICS – Simple phenomena of magnetism Attracted? Magnets Properties Have magnetic fields around them. .. or not? N S Attracted? Magnets Properties Have magnetic fields around them. Have two opposite poles (N & S) – like poles repel, unlike poles attract. N S .. may be? Attracted? Magnets Properties Have magnetic fields around them. Have two opposite poles (N & S) – like poles repel, unlike poles attract. N S .. possibly? Exert little or no force on a non-magnetic material. Attracted? Magnets Properties Have magnetic fields around them. Have two opposite poles (N & S) – like poles repel, unlike poles attract. N S Attract magnetic materials by inducing magnetism in them. Iron N Steel .. hopefully? Exert little or no force on a non-magnetic material. Attracted? Magnets Properties Have magnetic fields around them. Have two opposite poles (N & S) – like poles repel, unlike poles attract. N Attract magnetic materials by inducing magnetism in them. S N S S N N Poles induced in both iron and steel. .. mmmm? Exert little or no force on a non-magnetic material. Attracted? Magnets Properties Have magnetic fields around them. Have two opposite poles (N & S) – like poles repel, unlike poles attract. N Attract magnetic materials by inducing magnetism in them. S N YES!!! Exert little or no force on a non-magnetic material. S N Iron loses magnetism – it was only a temporary magnet Steel retains magnetism – it became a permanent magnet Magnets – make your own! How strong is it? N Not very. S S N Placing a piece of steel near a magnet makes it permanently magnetised, but its magnetism is usually weak. Magnets – make your own! How strong is it? Getting stronger. Wide sweep away from the steel N S Induced poles The magnet can be magnetized more strongly by stroking it with one end of a magnet Magnets – make your own! How strong is it? Steel Strongest! Coil The best way of magnetizing is to place the steel bar in a long coil of wire and pass a large, direct (one way) current through the coil. The coil has a magnetic effect which magnetizes the steel. Magnets – how do they work? Just what is happening inside the magnet to make it magnetic? N S Magnets – how do they work? We need to look closely at what is happening to the particles (electrons) inside the magnet. Just what is happening inside the magnet to make it magnetic? N S Magnets – how do they work? We need to look closely at what is happening to the particles (electrons) inside the magnet. Just what is happening inside the magnet to make it magnetic? N S In an unmagnetized material, the tiny electrons, or atomic magnets point in random directions. Magnets – how do they work? We need to look closely at what is happening to the particles (electrons) inside the magnet. Just what is happening inside the magnet to make it magnetic? N S When the material becomes magnetized, more and more of the tiny atomic magnets line up with each other. They act as one BIG magnet. Magnets – how do they work? We need to look closely at what is happening to the particles (electrons) inside the magnet. Just what is happening inside the magnet to make it magnetic? N S If a magnet is hit with a hammer, the tiny atomic magnets get thrown out of line again, so the material becomes demagnetised. Magnets – how do they work? We need to look closely at what is happening to the particles (electrons) inside the magnet. Just what is happening inside the magnet to make it magnetic? N S If a magnet is hit with a hammer, the tiny atomic magnets get thrown out of line again, so the material becomes demagnetised. A magnet will also become demagnetized if heated to high temperature. Magnetic and non-magnetic Magnetic and non-magnetic Magnetic material – can be magnetized, and is attracted to magnets. Strongly magnetic materials contain iron, nickel or cobalt (eg. Steel is mainly iron). Magnetic and non-magnetic Magnetic material – can be magnetized, and is attracted to magnets. Strongly magnetic materials contain iron, nickel or cobalt (eg. Steel is mainly iron). Ferromagnets Hard magnetic materials, eg. Steel, alloys (Alcomax, Magnadur). Difficult to magnetise, but do not lose their magnetism. Used for permanent magnets. Magnetic and non-magnetic Magnetic material – can be magnetized, and is attracted to magnets. Strongly magnetic materials contain iron, nickel or cobalt (eg. Steel is mainly iron). Ferromagnets Hard magnetic materials, eg. Steel, alloys (Alcomax, Magnadur). Difficult to magnetise, but do not lose their magnetism. Used for permanent magnets. Soft magnetic materials, eg. Iron, Mumetal. Relatively easy to magnetise, but magnetism is temporary. Used in electromagnets and transformers. Magnetic and non-magnetic Magnetic material – can be magnetized, and is attracted to magnets. Strongly magnetic materials contain iron, nickel or cobalt (eg. Steel is mainly iron). Ferromagnets Hard magnetic materials, eg. Steel, alloys (Alcomax, Magnadur). Difficult to magnetise, but do not lose their magnetism. Used for permanent magnets. Non-magnetic materials. Metals (brass, copper, zinc, tin and aluminium); non-metals. Soft magnetic materials, eg. Iron, Mumetal. Relatively easy to magnetise, but magnetism is temporary. Used in electromagnets and transformers. Magnetic fields Magnetic fields Iron filings sprinkled around a magnet Magnetic field lines around the magnet Magnetic fields Iron filings sprinkled around a magnet Field lines run from the north pole (N) to the south pole (S). The magnetic field is strongest where the field lines are closer together. Magnetic field lines around the magnet Magnetic fields Using a plotting compass to find the field lines. N S Magnetic fields Using a plotting compass to find the field lines. N S Magnetic fields Using a plotting compass to find the field lines. N S Magnetic fields Using a plotting compass to find the field lines. N S Magnetic fields Using a plotting compass to find the field lines. N S Magnetic fields Using a plotting compass to find the field lines. N S Magnetic fields Using a plotting compass to find the field lines. . . . . N S Magnetic fields Using a plotting compass to find the field lines. http://www.physbot.co.uk/magnetic-fields-and-induction.html Magnetic fields Interactions between magentic fields When unlike poles are placed near each other, their magnetic fields combine to produce a single field of almost uniform strength. http://www.homofaciens.de/technics-magnetic-field-energy_en_navion.htm Magnetic fields Interactions between magentic fields When unlike poles are placed near each other, their magnetic fields combine to produce a single field of almost uniform strength. http://www.homofaciens.de/technics-magnetic-field-energy_en_navion.htm Neutral point When like poles are placed near each other, their magnetic fields cancel each other, and there is a neutral point where the combined field strength is zero. The Earth’s magnetic field The Earth’s magnetic field is like that around a very large, but very weak, bar magnet. The Earth’s magnetic field The Earth’s magnetic field is like that around a very large, but very weak, bar magnet. A compass ‘north’ end points north. But a north pole is always attracted to a south pole, so the Earth’s magnetic south pole must actually be in the north. The Earth’s magnetic field The Earth’s magnetic field is like that around a very large, but very weak, bar magnet. A compass ‘north’ end points north. But a north pole is always attracted to a south pole, so the Earth’s magnetic south pole must actually be in the north. The Earth’s magnetic north is actually over 1200km away from the true geographic north pole. The Earth’s magnetic field Over a period of time the Earth’s magnetic pole will ‘flip’. The Earth’s magnetic field is like that around a very large, but very weak, bar magnet. A compass ‘north’ end points north. But a north pole is always attracted to a south pole, so the Earth’s magnetic south pole must actually be in the north. The Earth’s magnetic north is actually over 1200km away from the true geographic north pole. The Earth’s magnetic field Over a period of time the Earth’s magnetic pole will ‘flip’. The Earth’s magnetic field is like that around a very large, but very weak, bar magnet. A compass ‘north’ end points north. But a north pole is always attracted to a south pole, so the Earth’s magnetic south pole must actually be in the north. In the last 10 million years, there have been, on average, 4 or 5 ‘flips’ per million years. The Earth’s magnetic north is actually over 1200km away from the true geographic north pole. Electromagnets Distinguish between the design and use of permanent magnets and electromagnets Electromagnets Distinguish between the design and use of permanent magnets and electromagnets Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off. Electromagnets Distinguish between the design and use of permanent magnets and electromagnets Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off. Permanent magnet uses: 1. Needles of compasses. 2. Fridge door seals, holding the doors closed. 3. Loudspeakers and microphones. Electromagnets Distinguish between the design and use of permanent magnets and electromagnets switch Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off. Permanent magnet uses: 1. Needles of compasses. 2. Fridge door seals, holding the doors closed. 3. Loudspeakers and microphones. When a current flows through the coil it produces a magnetic field. This field is temporary and is lost when the current is switched off. battery coil Soft iron core Electromagnets Distinguish between the design and use of permanent magnets and electromagnets switch Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off. Permanent magnet uses: 1. Needles of compasses. 2. Fridge door seals, holding the doors closed. 3. Loudspeakers and microphones. When a current flows through the coil it produces a magnetic field. This field is temporary and is lost when the current is switched off. battery coil Soft iron core Strength increased by: - Increasing the current - Increasing number of turns Electromagnets Distinguish between the design and use of permanent magnets and electromagnets switch Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off. Permanent magnet uses: 1. Needles of compasses. 2. Fridge door seals, holding the doors closed. 3. Loudspeakers and microphones. When a current flows through the coil it produces a magnetic field. This field is temporary and is lost when the current is switched off. battery coil Soft iron core Strength increased by: - Increasing the current - Increasing number of turns Uses: scrapyard electromagnets, circuit breakers, relays, electric bells.
