Unit 10 Problems Solution

CC2404 Applied Physics and Instrumentation in Health Care Solution of Problems Unit 10 (2009)

1. The electromagnetic spectrum includes radio waves, microwaves, infra-red, visible light, ultraviolet, X-rays and gamma rays. a Which statement about electromagnetic waves is correct? A They all have the same wavelength. B They all have the same frequency. C They are all transverse waves. (Correct) b Name two types of electromagnetic wave used to cook food. (microwaves, infra-red) c Name one type of electromagnetic wave used to detect a break in a bone. (X-rays) (London Foundation, June 99) 2. Which of the following types of radiation has a the longest wavelength, (B radio waves) b the highest frequency (X-rays) A UV B radio waves C light D X-rays E IR 3. Name one type of electromagnetic radiation which a causes sun-tan, (UV) b is used for satellite communication, (radio waves) c is used to sterilize surgical instruments (UV) d is used in TV remote control (infra-red) 4. Which of the following is NOT a factor that would affect the amount of UV radiation reaching the ground? a. b. c. d.

Latitude Altitude Longitude Sun elevation

Ans. c

5. What is the possible long-term hazard of UV on human skin? a. induction of skin cancer b. reddening of the skin c. Vitamin D Ans. a 6. Which of the statement concerning the causes of suntan and sunburn is correct? a. b. c. d.

UV-A causes suntan and UV-B causes sunburn UV-A causes sunburn and UV-C causes suntan Both UV-A and UV-B will cause suntan but not sunburn Both UV-A and UV-B will cause sunburn but not suntan

Ans. a

7. a) b) c) d)

Decide each of the following statement true or false. A tan results from your body defending itself against further damage from UV radiation. (T) You can’t get sunburnt on a cloudy day. (F) You can’t get sunburnt while in the water. (F) UV radiation exposure is cumulative during the day. (T)

8. A VHF radio station transmits on a frequency of 100 MHz (1 MHz = 106 Hz). If the speed of radio waves is 3× 108m/s, a what is the wavelength of the waves, λ=

c 3 ×10 8 = m = 3m f 10 8

b how long does the transmission take to travel 60km? 60 ×10 3 t= s = 2 ×10 −4 s 8 3 ×10 c. What is its photon energy in J and in eV ? E = hf = 6.63 ×10 −34 J ⋅ s ×1 ×10 8 / s = 6.63 ×10 −26 J = 4.14 ×10 −7 eV