BASIC DC THEORY EXAM

1. A battery consists of two or more chemical cells connected in series.

2. The chemical cell is composed of two electrodes made of different types of metal or metallic compounds which are immersed in an electrolyte solution.

3. A line diagram is used to show the relationship between component groups, or stages in a circuit.

4. The total voltage across a series circuit is equal to the sum of the voltages across each resistor in the circuit.

5. The voltage flowing through each branch of a parallel circuit is equal to the total voltage in the circuit.

6. All voltages and currents have polarity as well as magnitude.

7. The direction of electron flow is from a point of negative potential to a point of positive potential.

8. The direction of positive charges, or holes, is in the opposite direction of electron flow. This flow of positive charges is known as “conventional flow.”

9. Kirchhoff’s voltage law states that the sum of the voltage drops around a closed loop is equal to the sum of the voltage sources of that loop.

10. Kirchhoff’s current law states that the current arriving at any junction point in a circuit is equal to the current leaving that junction.

11. The voltage flow at any element in a DC circuit can be determined using loop equations.

12. The voltage at any point in a DC circuit can be determined using node equations.

13. An open series DC circuit will result in no power being consumed by any of the loads.

14. An                              will oppose a change in current flow by the CEMF induced when the field collapses or expands.

15. A capacitor is constructed of two conductors (plates) separated by a dielectric.

16. An electrolyte is a solution which is capable of conducting an electric current. The electrolyte of a cell may be a liquid or a paste.

17. Specific gravity is defined as the ratio comparing the weight of any liquid to the weight of an equal volume of water.

18. A good example of a voltaic cell is one that contains iron and copper electrodes.

19. The purpose of a battery is to store chemical energy and to convert this chemical energy into electrical energy when the need arises.

20. A battery that is connected in parallel has the advantage of a greater                              .

21. The alkaline cell has the advantage of an extended life over that of a carbon-zinc cell of the same size.

22. The nickel-cadmium battery has the advantage of being a dry cell that is a true storage battery with a reversible chemical reaction.

23. To reduce the amount of gassing, charging voltages above                        volts per cell should be minimized.

24. Counter-electromotive force (CEMF) is defined as the induced voltage that acts to counter the applied voltage in a DC motor or a DC generator.

25. Applied voltage is defined as the current that is delivered across the load.

26. The voltage of a shunt-wound DC generator increase with an increase in load current.

27. The voltage of a series-wound DC generator increases sharply with an increase in load.

28. The                                         of an over-compounded DC generator gradually rises with an increasing load.

29. In a differentially-compounded DC generator, the series and shunt fields oppose one another.

30. The speed of a DC motor may be changed by using resistors to vary the field current and, therefore, the field strength.

31. A shunt-wound DC motor has a decreasing torque as speed increases.

32. A series-wound motor has a rapidly increasing torque when speed decreases.

33. As load is removed from a shunt-wound motor, the speed will increase sharply.

34. The advantages of a series-wound motor are that it develops a large torque and can be operated at low speed.

35. Starting resistors are necessary for large DC motors to prevent damage due to high currents while starting the motor.