FACULTY OF APPLIED SCIENCE. PHYSICS III. Please arrange the answers in the order of the questions. In the numerical problems, use the values g=1000 (c.g.s.) and 25/8. 1. Distinguish between magnetic force and magnetic induction; between permeability and susceptibility. 2. The field magnet of a dynamo consists of an iron ring, inside diameter 35 cm., outside diameter 45 cm., crosssection 25 sq. cm.; and two pole pieces, each 10 cm. long and 50 sq. cm. cross-section, which project toward the centre of the ring from opposite points on its inner surface. Taking the permeability of the iron as 800, find the number of ampere-turns required on each pole piece to make the field strength in the space between the pole pieces 1000 gausses. Assume no leakage of the lines. 3. Two permanent bar magnets, exactly alike, are each 20 cm. long, 2 cm. broad, and 0.5 cm. thick. Each weighs 160 gm. When placed in a vertical position, one above the other, the north pole of one in contact with the south pole of the other, the lower one can be just lifted by the upper one. Find (a) the intensity of magnetization; (b) the pole strength. 4. A straight uniform wire 80 cm. long has a resistance of 7.3 ohms. It is connected in series with a resistance of 2000 ohms and a battery of e.m.f. 4.1 volts. A thermo-couple with one junction kept at 0°C. and the other at 60°C. is in series with a galvanometer, and the free ends of this circuit are touched to two points on the stretched wire 24 cm. apart. The galvanometer remains undeflected. (a) What is the e.m.f. produced by the thermocouple? (b) What temperature of the warm junction is indicated when the length of stretched wire is 43 cm. for no deflection of the galvanometer? 5. A circular coil of 100 turns of wire, 32 cm. in diameter, is rotated about its vertical diameter in a horizontal magnetic field of 2000 gausses, at the rate of 8 revolutions per sec. If the resistance of the coil be 10 ohms, and its ends be joined, find the number of calories of heat developed in it per second. 6. Define the following terms: angle of lag, self-induction, frequency. (b) In a test of an alternating-current motor, an ammeter in series with the motor indicated 25 amp., a voltmeter across its terminals indicated 550 volts, and a wattmeter showed that the motor was using 6.875 kilowatts. Calculate the angle of lag. 7. A coil is attached to the 100-volt direct current mains, and a current of 12.5 amp. flows through it. Afterwards the same coil is attached to the 100-volt 60-cycle alternating current mains, and the current through it is then 10 amp. Calculate the inductance of the coil. FACULTY OF APPLIED SCIENCE. PHYSICS IV. 1. (a) Show that the potential at a point P at a distance r from a charge Q is equal to Q/r. (b) Show that the above result is true when the charge is distributed over a sphere and r is the distance of the point from the centre of the sphere, the point being outside the sphere. 2. (a) A charge of 20 electrostatic units is at the point whose rectangular coordinates are (10, 0). What is the value of the electric intensity at any point on the circumference of a circle whose radius is 5 units and whose centre is at the origin? (b) Determine the work done in moving a unit charge along the circumference of the circle from the point (5, 0) to the point (-5, 0) by integrating the tangential component of the force around the semi-circumference. 3. (a) Prove that the electric intensity just outside a charged conductor is equal to 4 times the surface density of the charge. (b) Explain one method for determining the value of the ratio of the charge to the mass for the cathode rays. 4. (a) Describe one method of determining the value of the mutual inductance of a pair of coils. In what unit is the result expressed and how is this unit related to the absolute C.G.S. unit of inductance? (b) Describe fully a method for measuring the resistance of a short copper bar. 5. A circular coil of 8 turns and radius 10 cm. is placed in a magnetic field whose intensity is 200 C.G.S. units so that its plane is inclined 30° to the direction of the field. What is the value of the torque experienced by the coil? 6. Prove that the quantity of electricity induced in a coil which is rotated through a certain angle in a magnetic field, is independent of the rapidity of turning. 7. Show that the capacity per unit length of a cylindrical condenser is equal to FACULTY OF APPLIED SCIENCE. ORGANIC CHEMISTRY I. 1. (a) Explain the laboratory method of obtaining absolute alcohol from a mixture of alcohol and water. (b) How would you prove the presence of nitrogen and bromine in an organic compound containing them? 2. (a) Give structural formulae of the pentanes. (b) How could you prove the structural formula assigned to ethyl alcohol? 3. (a) Illustrate by means of equations the principal reactions of primary aliphatic amines, alkyl halides, nitriles. (b) Describe in detail, giving all equations, the preparation and purification of aniline. 4. (a) Discuss the chemistry of carbohydrates under the following heads: classification, relation to other compounds, chemical properties. (b) What is urea and how prepared? 5. (a) Name the different classes of aromatic compounds containing nitrogen, and give the structural formula of each class. (b) Discuss the chemistry of the triphenylmethane dyes. |