4. Electricity and Magnetism Flashcards
(12 cards)
Describe the forces between magnetic poles, and between magnets and magnetic materials (use the terms north pole (N pole), south pole (S pole), attraction and repulsion, magnetised and unmagnetised)
- Magnets have two poles (ends where magnetic field/force is strongest at): North (N pole) and South (S pole)
- When two magnets are held close together, there’ll be a force between them. Like poles will repel and opposite poles will attract (this action is an example of a non-contact force)
- Magnetic materials (not magnets) are attracted to magnets, regardless of which pole is held close to it. While non-magnetic materials neither repel or attract to a magnet
Explain what causes magnetic forces
Magnetic forces (repulsion/attraction between magnets) are due to interactions between magnetic fields
Describe induced magnetism
- Induced magnetism: Caused when an induced magnet (a material with a soft iron core) becomes a magnet temporarily when it is placed in a magnetic field
- Induced magnets always cause a force of attraction with a permanent magnet (and then becomes a magnetised material)
- End of the induced magnet that is closest to the magnet will have an opposite pole to the magnet’s pole facing it
State the differences between the properties of temporary magnets (made of soft iron) and the properties of permanent magnets (made of steel
Permanent Magnets (e.g. steel):
- Made from magnetic materials (e.g. steel)
- Produces its own magnetic field
- Fixed north and south poles
- Always magnetised and cannot be easily demagnetised
Temporary Magnets (e.g. soft iron):
- Formed when placed in a magnetic field (e.g. near a permanent magnet)
- Magnetic field is induced (not self-produced)
- Induced poles are opposite to the nearby poles of the permanent magnet
- Magnetised only when inside a magnetic field
- Loses magnetism when removed from the magnetic field
State the difference between magnetic and non-magnetic materials
- Magnetic materials are materials that can be attracted to a magnet and can become magnetised (e.g. iron, steel, nickel, cobalt).
- Non-magnetic materials are materials that are not attracted to magnets and cannot be magnetised (e.g. plastic, wood, copper, aluminium).
Describe a magnetic field
A region in which a magnetic pole experiences a force
Describe the plotting of magnetic field lines with a compass or iron filings and the use of a compass to determine the direction of the magnetic field
- Iron fillings: Place a paper on top of the magnet. And gently sprinkle iron filings on top of it. Carefully tap the paper to allow the iron filings to settle on the field lines
- Compass:
1. Paper: Place the magnet on a sheet of paper and mark a dot close to one corner of the magnet
2. Place: Position a plotting compass next to the dot so that one end of its needle points towards it. Use a pencil to mark a new dot at the other end of the needle. Then, move the compass so it points toward this new dot
3. Repeat: Continue this process to create a chain of dots going from one end of the magnet to the other. Once done, remove the compass and smoothly connect the dots in a curve to form a magnetic field line
Describe the uses of permanent magnets and electromagnets
- Permanent magnets
1. Compasses: For navigation since the needle always points north (of the Earth, but magnetic S pole)
2. School lab experiments: Used in science demonstrations
3. Toys: Such as toy trains and trucks often have magnets which attach the carriages or trailers to the engine or cab
4. Fridge magnets: Made of flexible magnetic material or by sticking a magnet to the back of something - Electromagnets
1. MRI scanners (in hospitals): To produce diagnostic images of the organs of the body
2. Speakers and earphones: In devices. To sense or send sound waves
3. Recycling: Electromagnets can separate steel from other materials and metals. Once recovered, the steel is reused and recycled, reducing mining for iron ore and processing ore into steel
4. Mag-Lev trains: For them to hover, they’re repelled by large electromagnets on the train and track. Reducing friction and allowing speeds of nearly 400 miles per hour
Describe simple experiments to show the production of electrostatic charges by friction and to show the detection of electrostatic charges
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Explain that charging of solids by friction involves only a transfer of negative charge (electrons)
Charging by friction is when certain insulating solids are rubbed against each other to become electrically charged. Electrons transfer from one insulator to the other. So one gains a net positive charge and the other gains a net negative charge
Describe an experiment to distinguish between electrical conductors and insulators
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Recall and use a simple electron model to explain the difference between electrical conductors and insulators and give typical examples
a) Conductors
- Allows charge to flow through it easily
- Metallic conductors are made up of positively charged metal ions. With their outermost electrons delocalised. Hence, the electrons are free to move (able to carry charge)
- Metal conducts electricity because current is the rate of flow of the electrons. So, the more easily electrons are able to flow, the better the conductor
- Examples: Silver, copper, aluminium, and steel (usually metals)
b) Insulators
- No free charges. Therefore, doesn’t allow the flow of charge through it easily
- Some non-metals (e.g. wood) conduct electricity, as they allow some charge to pass through them. They aren’t good conductors, but conduct a little in the form of static electricity
- Examples: Rubber, plastic, glass, and wood
