CIE iGCSE Co-Ordinated Science P5.2.4 Half-life Exam Style Questions Paper 3
Question
(a) High frequency sound waves are called ultrasound.
An ultrasound wave travels 13.5cm in 0.000090s through water.
Calculate the speed of the ultrasound wave in m/s.
speed = …………………………………………. m/s
(b) Ultrasound waves are used in hospitals to scan unborn babies.
(i) Suggest a reason why it is not safe to scan unborn babies with X-rays.
(ii) State one use for X-rays in a hospital.
(c) (i) γ-radiation is used in hospitals to kill cancerous cells.
Fig. 3.1 shows an incomplete electromagnetic spectrum.
Write γ-radiation in its correct place.
(ii) A source of γ-radiation in a hospital is technetium-99.
Technetium-99 has a half-life of 6 hours.
The source contains 1280 undecayed atoms.
Calculate how many atoms will have decayed after 12 hours.
number of decayed atoms = …………………………………………………
▶️Answer/Explanation
Ans : 3(a) evidence of 13.5 cm = 0.135 m ;
evidence of speed = distance / time (in any form) or 0.135 / 0.000090;
= 1500 (m / s) ;
3(b)(i) ionising radiation damages / kills human cells or damages DNA ;
3(b)(ii) observing broken bones etc ;
3(c)(i) ϒ – radiation on left hand side ;
3(c)(ii) 2 half lives ; (320 remain so ) 960 atoms decayed ;