gcse lock innnn Flashcards
What is the difference between soft and hard magnetic materials?
Soft magnetic materials are easily magnetised and demagnetised, ideal for applications requiring rapid changes in magnetisation.
Hard magnetic materials retain their magnetisation and are used for permanent magnets.
Describe the construction of electromagnets.
An electromagnet is constructed by wrapping a coil of wire around a soft iron core and passing an electric current through the wire, which creates a magnetic field.
How do you change the strength of an electromagnet?
To make an electromagnet stronger:
- Increase current flowing through the coil of wire
- Add more turns to the coil
- If you haven’t already, make sure the core is made of iron
To make an electromagnet weaker:
Opposite of above
What happens to a charged particle when it moves in a magnetic field?
A magnetic field exerts a force on a moving charged particle
This force is always perpendicular to both the direction of the particles motion and the direction of the magnetic field
The force causes the charged particle to change direction, resulting in a curved path
You can determine the direction of the force using Fleming’s Left-Hand Rule
However, if the particle is moving parallel to the magnetic field lines, it experiences no force
What happens when a charged particle enters a magnetic field perpendicular to its velocity?
It moves in a circular path because the magnetic force always acts as a centripetal force, towards the centre of the circle.
How does a DC motor work?
A coil of current carrying wire is positioned between two poles of a permanent magnet. Each end of the coil is attached to a split ring commutator which is attached to a battery powered circuit.
- Current in the left hand part of the coil causes a downward force, and current in the right hand part of the coil causes an upward force.
- The coil rotates anti-clockwise because of the forces described above.
- When the coil is vertical, it moves parallel to the magnetic field, producing no force. This would tend to make the motor come to a stop, but two features allow the coil to continue rotating.
- The momentum of the motor carries it on round a little.
- A split ring commutator changes the current direction every half turn
- One the conducting brushes reconnect with the commutator after a half turn, current flows in the opposite directing and each side of the coil is now near the opposite magnetic pole
- This means that the motor effect forces continue to cause anti-clockwise rotation of the coil.
How does a loudspeaker work?
- A current in the coil creates a magnetic field
- The magnetic field interacts with the permanent magnet, generating a force, which pushes the cone outwards
- The direction of the magnetic field reverses because it is an AC current
- The force on the cone now pulls it back in
- Repeatedly alternating the current direction makes the cone vibrate in and out
- The cone vibrations cause pressure variations in the air - which are sound waves.
What is a dynamo?
A DC generator that converts mechanical energy into electrical energy
How does a dynamo work?
A simple DC generator consists of a coil of wire rotating in a magnetic field. However, it uses a split ring commutator rather than the two slip rings found in AC generators.
In a dynamo, a split ring commutator changes the coil connections every half turn. As the induced potential difference is about the change direction, the connections are reversed. This means that the current to the external circuit always flows in the same direction.
How does an AC generator work?
The coil is rotated by an external force so that the movement of the coil interacts with the magnetic field of the permanent magnet. This induces an AC current.
The slip rings prevent the tangling of wires and allow a continuous and unbroken electrical connection between the rotating coils and the stationary external circuit.
What do becquerels measure?
The activity of a radioactive source, specifically the number of radioactive nuclei that decay per second.
Compare the ionising ability of alpha particles, beta particles and gamma rays.
Alpha particles are the most ionising, followed by beta particles and then gamma rays, which are the least ionising.
Which nuclear particle has the best penetrating power?
Alpha particles have the lowest penetrating power and can be stopped with a sheet of paper.
Why does gravitational field strength vary?
It’s directly related to the mass of the celestial body and inversely proportional to the square of the distance from its centre
How can stars be classified according to their colour?
Stars are classified by their colour, which directly relates to their surface temperature. Hotter stars appear blue, while cooler stars appear red.
Describe the life cycle of a star with a mass similar to the Sun.
- Nebula - cloud of gas and dust drawn together by gravity.
- Protostar - the contents heat up and the hydrogen nuclei start to fuse together to make helium.
- Main sequence - This is a stable sequence in the stars life where the force of gravity holding the star together is balanced by higher pressure due to the high temperatures.
- Red Giant Star - When all the hydrogen has been used up in the fusion process, larger nuclei begin to form and the star may expand to become a red giant.
- White dwarf - When all the nuclear reactions are over, a small star like the Sun may begin to contract under the pull of gravity.
Describe the life cycle of a star with a mass greater than the Sun.
Same as with a similar mass to the Sun until after main sequence.
After main sequence:
4. Red Super Giant - When all the hydrogen has been used up in the fusion process, larger nuclei begin to form and the star may expand to become a red giant.
5. Supernova - A larger star with more mass will go on making nuclear reactions, getting hotter and expanding until it explodes as a supernova.
6. Black hole or neutron star
How can the brightness of a star at a standard distance be represented?
Using absolute magnitude
What are the main arguments in favour of the Big Bang?
Cosmic Microwave Background Radiation
Red shift
How does red shift provide evidence for the Big Bang Theory?
Astronomers have discovered that, in general, the further away a galaxy is, the more red shifted its light is. This means that the further away the galaxies are, the faster they are moving. This is similar to an explosion, where the bits moving fastest travel furthest from the explosion. Red shift data provides evidence that the Universe, including space itself, is expanding.
How does red shift work?
Light from a star does not contain all the wavelengths of the
electromagnetic spectrum
. Elements in the star absorb some of the emitted wavelengths, so dark lines are present when the spectrum is analysed. Different elements produce different patterns of dark lines. The diagram shows part of the emission spectrum of light from the Sun.
List the electromagnetic spectrum in order of decreasing wavelength.
- Radiowaves
- Microwaves
- Infrared
- Visible light
- Ultraviolet
- X-ray
- Gamma rays
Rats and Mice In Venice Use eXtra Gondolas
What is the frequency of radiowaves and what can they be used for?
Communication
Radar
How can a chain reaction be set up in the process of fission?
- A ‘slow’ neutron is absorbed by a uranium-235 nucleus
- The resulting nucleus of uranium-236 is unstable
- Uranium-236 is unstable and splits apart
- The decay are the two daughter nuclei of barium-144 and krypton-89
- If more than one neutron from each fission causes fission in surrounding nuclei, the reaction escalates
- This is called chain reaction
- This involves sudden release of enormous heat energy and radiation
What role do the control rods play in the fission process?
The control rods are raised and lowered to stop neutrons from travelling between fuel rods and therefore change the speed of the chain reaction
Made of boron
What role does the graphite core play in the fission process?
Graphite slows the neutrons down so that they are more likely to be absorbed into a nearby fuel rod
What role does the coolant play in the fission process?
This is heated up by the energy released from the fission reactions and is used to boil water to drive turbines in the power station
What role does the concrete shield play in the fission process?
The daughter products of the fission reaction are radioactive and can be a hazard
What role does the nuclear fuel play in the fission process?
The fuel is held in rods so that the neutrons released will fly out and cause nuclear fission in other rods
Describe the process of nuclear fission.
- Nuclear fission is the splitting of a large atomic nucleus into smaller nuclei
1. A neutron is absorbed into a nucleus (typically uranium-235)
2. This causes the nucleus to become uranium-236, which is violently unstable
3. The entire nucleus splits into two large fragments called ‘daughter nuclei’. In addition to the ‘daughter’ products, two or three neutrons also explode out of the fission reaction.
4. These other neutrons can also collide with other uranium nuclei to cause further fission reactions, creating a chain reaction
5. The fast moving neutrons carry most of the energy from the reaction with them but before the neutrons can collide with fresh uranium nuclei, they need to be slowed down
6. This is so that the energy can pass on to other components in the nuclear reactor, which is used to heat water to drive the turbines that turn the generators
Describe the process of nuclear fusion.
- Nuclear fusion is when two small, light nuclei join together to make one heavy nucleus. Fusion reactions occur in stars where two hydrogen nuclei fuse together under high temperatures and pressure to form a nucleus of a helium isotope.
