BRAINCAKEMagnetism and magnetic fields
Revision notes for Magnetism and magnetic fields in OCR Physics A (J249). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- Attraction and repulsion between magnetsA permanent magnet has two ends, called poles.
- Permanent and induced magnetsA permanent magnet produces its own magnetic field all the time.
- Magnetic fields and field linesA magnetic field is the region around a magnet where a magnetic material, or another magnet, feels a force.
- The Earth's magnetic field and compassesA plotting compass is a small magnet on a pivot, free to turn.
- Magnetic fields around a current-carrying wireAn electric current has a magnetic effect.
- Strength of the field around a conductorThe magnetic field around a wire carrying a current is not the same strength everywhere.
- Solenoids and the magnetic effectA current in a straight wire makes only a weak magnetic field.
- The force between a magnet and a current-carrying conductorA wire carrying a current is surrounded by its own magnetic field.
- Fleming's left-hand ruleFleming's left-hand rule shows how the force, the current and the magnetic field are arranged relative to each other.
- Calculating the force on a conductorThe force on a straight conductor carrying a current at right angles to a magnetic field can be calculated using: force (N) = magnetic flux density…
- Electric motorsAn electric motor uses the force on a current-carrying wire in a magnetic field to produce rotation.
- Induced potential differenceIf a conductor and a magnetic field move relative to each other so that the magnetic field around the conductor changes, a potential difference is…
- Alternators and dynamosAn alternator generates a.c.
- How a transformer worksA transformer is made of two coils of insulated wire wound on the same iron core.
- Turns ratio and potential difference in a transformerThe ratio of the potential differences across the two coils of a transformer is equal to the ratio of the numbers of turns on the coils.
- Transformer calculationsThe transformer equation is Vs / Vp = Ns / Np.
- Microphones, loudspeakers and headphonesA sound wave is a series of pressure variations in the air.