# Using Magnetic Fields to Keep Things Moving

HideShow resource information
• Using Magnetic Fields to Keep Things Moving
• Electromagnets
• The forces between two magnets: like poles repel; unlike poles attract.
• A magnetic field line is the line, along which a plotting compass points.
• An electromagnet consists of a coil of insulated wire, wrapped round an iron core.
• Electromagnets are used in scrapyard cranes, circuit breakers, electric bells, and relays.
• The Motor Effect
• In the motor effect, the force:
• is increased if the current of the strength of the magnetic field is increased.
• is at right angles to the direction of the magnetic field, and to the wire.
• is reversed if the direction of the current or the magnetic field is reversed.
• An electric motor has a coil, which turns when a current is passed through it.
• Electromagnetic Induction
• When an electromagnet is used, it needs to be switched on or off to induce a pd.
• Electromagnetic induction is the process of creating a pd, using a magnetic field.
• When a conductor cuts the lines of a magnetic field, a pd is induced across the ends of the conductor.
• Transformers
• A transformer has an iron core, unless it is a switch mode transformer, which has a ferrite core.
• A transformer only works on AC because a changing magnetic field is necessary to induce AC in the secondary coil.
• A switch mode transformer is lighter and smaller than an ordinary transformer.It operates at high frequency.
• Transformers in Action
• Transformers are used to step pd up or down.
• For a step-down transformer, n(s) is less than n(p). For a step-up transformer, n(s) is greater than n(p).
• The transformer equation is: V(p)/V(s) = n(p)/n(s)
• V(p) is the primary pd
• V(s) is the secondary pd
• n(p) is the number of primary turns
• n(s) is the number of secondary turns
• For a 100% efficient transformer, V(p) x I(p) = V(s) x I(s)
• I(p) is the current in the primary coil
• I(s) is the  current in the secondary coil
• A Physics Case Study
• We measures blood pressure, ECG potential differences, and exposure to ionising radiation in hospitals.
• We use physics in hospitals whenever:
• blood pressure (or temperature) is measured.
• an ECG recording is made.
• an endoscope is used.
• a scanner is used.
• Untitled
• Transformers
• A transformer has an iron core, unless it is a switch mode transformer, which has a ferrite core.
• A transformer only works on AC because a changing magnetic field is necessary to induce AC in the secondary coil.
• A switch mode transformer is lighter and smaller than an ordinary transformer.It operates at high frequency.