Physic Unit 3 Chapter 2
- Created by: A.B.
- Created on: 17-04-13 17:27
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- Physics Unit 3 Chapter 3
- Electromagnets
- The force 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.
- The magnetic field of the wire magnetises the iron bar strongly and when the current is switched off the iron loses most of its magnetism.
- Iron easily loses it magnetism whereas steel is unsuitable because it keeps it magnetism when the current is switched off.
- The magnetic field of the wire magnetises the iron bar strongly and when the current is switched off the iron loses most of its magnetism.
- Electromagnets are used in scrapyard cranes, circuit breakers, electric bells and relays.
- Untitled
- The Motor Effect
- In the motor effect, the force:
- Is increased if the current or the strength of the magnetic field is increased.
- It is 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.
- Fleming's LH Rule
- First finger - field. Second finger - Current. ThuMb - Movement.
- In the motor effect, the force:
- The Motor Effect
- Electromagnetic Induction
- Electromagnetic induction is the process of creating a potential difference using a magnetic field.
- When a conductor cuts the lines of a magnetic field, a potential difference is induced across the ends of the conductor.
- When an electromagnet is used, it needs to be switched on or off to induce a pd.
- Transformers
- A transformer only works on ac because a changing magnetic field is necessary to induce ac in the secondary coil.
- A transformer has an iron switch mode transformer which has a ferrite core.
- A switch mode transformer is lighter and smaller than an ordinary transformer. It operates at high frequency.
- A step up transformer must have more turns (coils) around the secondary coil than the primary coil.
- Transformers in Action
- Transformers are used to step potential differences up or down.
- The transformer equation is primary pd/secondry pd.= number of primary turns/number of secondry turns.
- For a step down transformer, the number of secondary turns is less than the number of primary turns and vice versa.
- For a 100& efficient transformer, power supplied to the transformer = power delivered by the transformer which is primary current x voltage = secondary current x voltage.
- The higher the grid pd, the greater the efficiency of transferring electrical power through the grid.
- Pd = number of turns.
- A Physics Case Study
- We use physics in hospital whenever: -blood pressure (or temperature) is measured - an ECG recording is made - an endoscope is used - a scanner is used.
- We measure blood pressure, ECG potential differences and exposure to ionising radiation in hospitals.
- A CT scanner uses X-rays, which are ionising radiation and therefore can damage living tissue.
- Electromagnets
- We use physics in hospital whenever: -blood pressure (or temperature) is measured - an ECG recording is made - an endoscope is used - a scanner is used.
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