Intermediate physics / by W. Watson.

  • Watson, W. (William), 1868-1919.
Date:
1912
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Licence: In copyright

Credit: Intermediate physics / by W. Watson. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    CHAPTER IV 1. Two small conducting spheres, each weighing O'l gram, are suspended by silk fibres 1 metre long, the upper ends being at the same level and 5 cm. apart. What charge must be comnumicated to each sphere so that they may come to rest at a distance of 3 cm. apart ? 2. A condenser is formed by two parallel co-axial circular discs of 20 cm. radius, 1 mm. apart. Neglecting the effect of the edges, calculate the capacity when the dielectric is air. What is the energy of the charge when the charge on the insulated plate is 100 electrostatic units ? 3. Give an account of the Leyden jar, and state on what the charge it receives will depend. If you are given two Leyden jars, a source which will charge them at given potential, and a gold-leaf electroscope, how can you find which has the greater capacity ? 4. Find the work necessary to withdraw the plates of an air condenser through 0'2 cm. if charged with 600 electrostatic units of electricity. The plates are discs 30 cm. in diameter, and are 1 cm. apart. What becomes of the work done ? 5. Explain what is meant by the capacity of a condenser. The capacities of two Leyden jars are 6\ and C^,; compare the energies of their charges under the following conditions : («) when their charges are equal, and (6) when the difference of potential between the coatings is the same. 6. Two insulated metal spheres of radii 5 and 7 cm. are placed at a considerable distance apart and charged positively with 10 and 6 units respectively. What will be the charges on the spheres after they have been connected by a fine insulated wire ? 7. If the spheres in the above question are brought near together, will their respective electrical states be altered, and if so, in what direction ? 8. A hollow insulated conductor is electrified positively. A gold-leaf electroscope is electrified negatively, and a small conducting sphere connected by a thin wire to the electrosco^Je is (1) brought near the conductor, (2) introduced, and (3) made to touch the inside. Describe and explain the indications of the electroscope. 9. Find an expression for the energy of a charged condenser, defining carefully Avhat is meant b}'' the quantities in terms of which you express the energy. 10. Show that the capacity of a condenser consisting of two concentric spherical shells of nearly equal radius is equal to SKj4.ird, where S is the surface of either shell, d the difference in their radii, and K the specific inductive capacity of the medium between the shells. 11. Describe a form of attracted disc electrometer. If the movable disc has a diameter of 5 cm. and the distance apart of the discs 0*5 is cm., calculate the P.D. when the pull on the movable disc is 800 dynes. 12. Explain what is meant by the potential and the electric intensity at a point in the air. How would you actually determine the potential at a given point in the air ? CHAPTER V 1. State Ohm's law and explain its meaning. A galvanometer has a resistance of 10 ohms, and gives a deflection of one scale division when traversed by a current of 10~^ amperes. Wliat resistance must be placed in series with the galvanometer so that it may give a deflection of 100 divisions Avhen a P.D. of 100 volts is applied ? 2. The E.M.F. of a battery is 4 volts and its internal resistance is 1*5 ohms. If the poles are joined by a wire of which the resistance is 20 ohms, calculate the current produced and the difference of potential between the ends of the wire.