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Questions and Answers
According to the right-hand rule, what happens to the direction of the magnetic field if the direction of the current in a conductor is reversed?
According to the right-hand rule, what happens to the direction of the magnetic field if the direction of the current in a conductor is reversed?
What is the primary difference between the magnetic field of a bar magnet and that of a current-carrying solenoid?
What is the primary difference between the magnetic field of a bar magnet and that of a current-carrying solenoid?
What happens to the magnetic field lines in a loop of wire when the current is increased?
What happens to the magnetic field lines in a loop of wire when the current is increased?
How does the magnetic field of an electromagnet differ from that of a permanent magnet?
How does the magnetic field of an electromagnet differ from that of a permanent magnet?
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What is the primary reason Earth has a magnetic field?
What is the primary reason Earth has a magnetic field?
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What is the SI unit of magnetic flux density?
What is the SI unit of magnetic flux density?
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What is Faraday's Law?
What is Faraday's Law?
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What is the direction of the force on a charged particle moving through a magnetic field?
What is the direction of the force on a charged particle moving through a magnetic field?
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What is mutual induction?
What is mutual induction?
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What is the formula for the induced emf in a solenoid?
What is the formula for the induced emf in a solenoid?
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What is the formula for the force on a current-carrying conductor in a magnetic field?
What is the formula for the force on a current-carrying conductor in a magnetic field?
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What is the formula for the force on a charged particle moving through a magnetic field?
What is the formula for the force on a charged particle moving through a magnetic field?
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Study Notes
Magnetism
- Magnetism is a phenomenon where certain materials exert attractive or repulsive forces on other materials.
- Every magnet has two poles: the north-seeking pole (north pole) and the south-seeking pole (south pole).
- A magnetic field is a region around a magnet where the magnet has an effect.
Magnetic Field
- A magnetic field line indicates the direction a 'magnetic north' would travel in a magnetic field if free to do so.
- Magnetic field lines can be plotted by placing a bar magnet on a blank sheet of paper and using a plotting compass.
- The Earth has a magnetic field around it, which behaves as though there was a giant bar magnet going through the centre of the Earth.
Magnetic Field of a Current-Carrying Conductor
- Every current-carrying conductor has a magnetic field around it caused by the current.
- The right-hand rule states that if the right hand clasps a conductor with the thumb pointing in the direction of the current, then the fingers give the direction of the magnetic field around the conductor.
Types of Magnetic Fields
- For a long straight wire, the field is a series of circles around the wire.
- For a solenoid, the field looks the same as a bar magnet.
- For a loop of wire, the field lines form circles around the loop.
Electromagnets
- An electromagnet is a magnet constructed from a soft iron core with a coil of wire wound around it.
- A magnetic field is set up when an electric current is passed through the wire and disappears when the current stops.
- Electromagnets are used in scrapyards, particle accelerators, and loudspeakers.
Magnetic Flux Density
- Magnetic flux density (B) is a measure of the strength of the magnetic field.
- It is a vector quantity with an SI unit of tesla (T).
- Its direction is along the field lines from north to south.
Force on a Current-Carrying Conductor
- The force on a current-carrying conductor in a magnetic field is given by F = IlB, where F is the force, I is the current, l is the length, and B is the magnetic field.
- The direction of the force can be determined using Fleming's left-hand rule.
Electromagnetic Induction
- Electromagnetic induction is where an emf is induced by a change in the magnetic flux linking a circuit.
- Magnetic flux (Φ) is the total amount of magnetic field in a given region; it is the product of magnetic flux density (B) and area (A).
- Faraday's law states that the magnitude of the induced emf is proportional to the rate of change of flux linking a circuit.
Faraday's Law and Lenz's Law
- Faraday's law states that induced emf = -N(dΦ/dt), where N is the number of turns in the coil.
- Lenz's law states that the direction of the induced emf is always such as to oppose the change causing it.
Applications of Electromagnetic Induction
- Generators convert mechanical energy into electrical energy by rotating a coil of wire within a magnetic field, causing flux to constantly change, thus inducing an EMF.
- Transformers are used to change the voltage of a.c. power supplies.
- Mutual induction is where a changing magnetic field in one coil induces an emf in another coil.
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Description
Learn about the fundamental concepts of magnetism, including magnetic poles, magnetic fields, and magnetic field lines. Understand how magnets exert attractive or repulsive forces on other materials.
