Physics 2012 Waec Past Questions and Answers

Question 61 :

• WAEC 2012

(a) Define magnetic line of force.
(b) A wire of length 10 cm carrying a current of 4.0 A is placed between the poles of a powerful electromagnet of magnetic flux density 2.0 T. Calculate the:
(i) force on the wire when it is parallel to the field;
(ii) maximum force on the wire;
(iii) force on the wire when it makes an angle of 60° with the field.
(c) Describe how keepers can be used to preserve the magnetic strength of permanent bar magnets.
(d) A sailor observes that his mariners' compass reads N 10° W at a place where the angle of declination is N15° W. Calculate the true bearing of the place.

Question 62 :

• WAEC 2012

(a) (i) Explain why x-rays can be used to produce photographs of fractures in bones.
(ii) List four uses of x-rays other than in medicine.
(b) State the energy transformations which takes place during the operation of an x-ray tube.
(c) (i) Explain three named dangers to which human beings may be exposed when subjected to large doses of x-rays.
(ii) State two precautions that must be taken by persons working with x-rays.
(d) In an x-ray tube, an electron is accelerated from rest towards a tungsten target biased at a potential of 33 kV. Calculate, for the electron, the
(i) kinetic energy;
(ii) velocity. [h = 6.6 x 10\(^{-14}\) Js; Me = 9.1 x10\(^{-31}\) kg; c = 3.0 x 10\(^4\) ms\(^{-1}\); e = 1.6 x 10\(^{-19}\) C.]