Older MCQs might not have the typical A, B, C,
D
choices. They
have choices 1, 2, 3, and a combination of them is the answer. Below is the key that maps such
combinations to the answer.
A
1, 2 and 3 are correct
B
1 and 2 only are correct
C
2 and 3 only are correct
D
1 only is correct
Describe the role of the following components in the stated applications: (a) radio waves – radio and television communications, astronomy (b) microwaves – satellite television, mobile (cell) phone, Bluetooth, microwave ovens (c) infrared – household electrical appliances, remote controllers, intruder alarms, thermal imaging, optical fibres (d) visible light – photography, vision (e) ultraviolet – security marking, detecting counterfeit bank notes, sterilising water (f) X-rays – hospital use in medical imaging, security scanners, killing cancerous cells, engineering applications such as detecting cracks in metal (g) gamma rays – medical treatment in detecting and killing cancerous cells, sterilising food and medical equipment, engineering applications such as detecting cracks in metal
State the approximate range of frequencies audible to humans as 20Hz to 20000Hz
