1. What is the resistance of an electric bell circuit where the E.M.F. is 3 volts and the current is 0.6 ampere? 2. A telegraph wire is broken somewhere, the ends lying upon damp ground. If an E.M.F. of 30 volts is applied from the ground to the wire and a current of 0.1 of an ampere flows, what is the resistance of the part connected to the ammeter. (The earth which completes the circuit from the end of the wire has very small resistance.) Why? 3. How far away is the break in the wire if the latter has a resistance of 80 ohms to the mile? Diagram. 4. What current will flow through a bell circuit of 8 ohms resistance if it contains three cells _in series_ each with an E.M.F. of 1.5 volts and an internal resistance of 1/3 ohm? 5. If the same three cells are connected in parallel on the same circuit what current flows? Is the current in problem 4 or 5 the larger? Why? 6. If four cells each with 1.5 volts E.M.F. and an internal resistance of 0.4 ohm are connected with a circuit having an external resistance of 0.8 ohm, what current will the parallel connection give? The series connection? Which gives the larger current? Why? 7. Four Daniell cells each having 1 volt E.M.F. and 3 ohms internal resistance are connected in series with 2 telegraph sounders of 4 ohms each. The connecting wires have 6 ohms resistance. Find the current intensity. 8. A battery of 2 cells arranged in series is used to ring a door bell. The E.M.F. of each cell is 1.5 volts, internal resistance 0.3 ohm, and the resistance of the bell is 4 ohms. What is the current in amperes? 9. In the above problem find the current if the cells are connected in parallel. CHAPTER XIII THE CHEMICAL AND HEAT EFFECTS OF ELECTRIC CURRENTS (1) THE CHEMICAL EFFECT OF AN ELECTRIC CURRENT =280. Electroplating.=--If two carbon rods (electric light carbons answer very well) are placed in a solution of _copper sulphate_ (Fig. 260) and then connected by wires to the binding posts of an electric battery, one of the rods soon becomes covered with a coating of _metallic copper_ while bubbles of gas may be seen upon the other carbon. If a solution of _lead acetate_ is used in the same way a deposit of _metallic lead_ is secured, while a solution of _silver nitrate_ gives silver. [Illustration: FIG. 260.--Two carbons placed in a solution of copper sulphate.] [Illustration: FIG. 261.--An electroplating bath.]