The image shows a magnetic resonance imaging scanner in a hospital. The patient lies on a bed that moves into the circular scanner. Powerful electromagnets ...
Question 1 Report
The image shows a magnetic resonance imaging scanner in a hospital. The patient lies on a bed that moves into the circular scanner. Powerful electromagnets create a magnetic field around the patient. The scanner is used by doctors to form images of soft tissues without using ionising radiation. Before a scan, staff ask whether the patient has a metal implant, jewellery or a magnetic card. A steel object could experience a large force in the field.
(a) What type of magnet is used to create the main field in the scanner? [1]
(b) Which object is most dangerous near the scanner: a steel key or a wooden ruler? [1]
(c) When a current in an electromagnet is increased, what happens to its magnetic field strength? [1]
(d) Sketch why a loose steel object can move towards the scanner. [1]
(e) What safety action should staff take before moving a patient into the scanner? [1]
A science club builds a crane to sort scrap metal. Fig. 1 shows the circular coil at the end of the crane cable. The coil is connected to a battery through a switch and is wrapped around an iron cylinder. The operator closes the switch only while lifting steel cans. Aluminium drinks cans must not be picked up. After each lift, the operator opens the switch so the load falls into a collection box. The diagram is not drawn to scale.
(a) What material should be used for the cylinder inside the coil? [1]
(b) Which type of can will the crane lift: aluminium or steel? [1]
(c) When the operator opens the switch, what happens to the magnetic field of the coil? [1]
(d) Sketch the field pattern around one end of the electromagnet, including arrows. [1]
Answer Details
MRI scanner
- (a) The main field is produced by an electromagnet. [1]
- (b) A steel key is most dangerous because steel can be magnetised and attracted strongly; a wooden ruler is not magnetic. [1]
- (c) Increasing current makes an electromagnet's magnetic field stronger. [1]
- (d) A loose steel object becomes magnetised in the scanner field and is attracted towards the strong-field region. [1]
- (e) Staff should check for and remove metal objects and check for implants before the patient enters the scanner. [1]
Scrap-metal crane
- (a) The cylinder should be soft iron. [1]
- (b) The crane lifts steel cans, not aluminium cans. [1]
- (c) Opening the switch stops the current, so the coil's magnetic field disappears or becomes zero. [1]
- (d) Field lines curve out of one end of an electromagnet and enter the other, with arrows in a consistent direction. [1]
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