Magnetism

Question 1

Define magnetism

Answer 1

The force exerted when magnets repel/attract one another

Question 2

What causes magnetism?

Answer 2

The motion of electrical charges (electrical current) so electrons act like tiny magnets
When electrons move in the same direction they are highly magnetic (half full shells)

Question 3

What is magnetization?

Answer 3

Magnets can cause magnetic substances to become a magnet like itself by running a magnet over an unmagnetized piece of material

Question 4

What are magnetic fields?

Answer 4

Substances that are magnetic will have their own magnetic field (the area around the magnet)
The further from the magnet, the weaker the forces will be

Question 5

Magnetic flux

Answer 5

Measurement of the total magnetic field passing through a given area (Tesla)

Question 6

Ferromagnetic

Answer 6

Becomes strongly magnetized when placed in a strong magnetic field (stays magnetized when field is removed)

Question 7

Diamagnetic

Answer 7

If you place a diamagnetic item in a magnetic field, it will become a temporary magnet to try and resist the magnetic field

Question 8

Paramagnetic

Answer 8

The item will align itself, so its electrical charge are moving the same way as the magnetic fields

Question 9

Static magnetic field/ Permanent Magnet

Answer 9

Permanent, with a magnetic field due to its own internal electron charges
(always on in an MRI)

Question 10

Electromagnets

Answer 10

Coil of metallic wire, run an electrical current through it = induced magnetic field
(turned on and off throughout a scan)
More coils=more strength of magnetic field

Question 11

Superconducting magnets

Answer 11

Work at very low temperatures so require liquid Helium (cryogenic) to keep the temp low
There is virtually no resistance and large currents, so has a very strong constant magnetic field (better images)

Question 12

How do magnets work in MRI?

Answer 12

Uses Hydrogen protons which have electrical charge in the body
They will align with a magnetic field (paramagnetic)
To detect signal, we knock them out of alignment and sample them as they realign
We can also produce gradient fields which can distort the main magnetic field so we can detect protons when they try and realign with the main magnetic field again

Question 13

How are High Tension Transformers used in radiography?

Answer 13

Used to change low voltage, high current mains electricity into high voltage, low current supply that X-ray tubes use

Question 14

What is resonance?

Answer 14

A large selective response of an object or system that vibrates with an externally applied force