INTRODUCTORY. 



Answer. Cos X + k cos 2 = constant, where k is the ratio of the poles' 

 strengths ; and 1? 0. 2 have the same meanings as in Question 2. 



4. What current must pass through a solenoid having ten turns per centimetre 

 of length in order that the field strength in its interior may be STT units ? 



Answer. 1'25 amperes. 



5. Show that if two coils are so situated that all the lines of force due to a 

 current passing through one coil interlinks the other, then the coefficient mutual 

 induction of the two coils is the square root of the product of the coefficient of 

 self-induction of the two coils. 



6. What is the energy of charge of a condenser whose capacity is 5 micro- 

 farads when its potential is 1 volt? What is the charge on the condenser? 



Answers. 25 ergs ; 5 x 10~ 7 coulombs. 



7. What is the specific inductive capacity of the dielectric when the mutual 

 force exerted by two quantities of electricity, each equal to 100 coulombs, 

 situated 10 centimetres apart, is 0'5 dyne? 



Answer. 2. 



8. Show that lines of force always cut the equipotential surfaces at right 

 angles. 



9. Show that the self-induction of a coil is proportional to the square of its 

 number of turns. 



