Man's physical universe

xanabras

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508 MAGNETISM AND ELECTRICITY

7. What is tlu" principle of galvanometers and other electrical measuring instruments?

8. Should scientists be concerned about the practical importance of their

researches?

9. What contributions did Lord Kelvin make to the field of electricity?

10. If you face the direction of flow of an electric current through a wire, will the

direction of the magnetic lines of force be clockwise or counterclockwise?

1 1 Which hand should you place around a wire so that the finger will point in the

direction of the magnetic field when the thumb points in the direction of

electron flow?

12. Diagram the magnetic field surrounding a trolley wire. Have you ever observed

the eff^ect of such a magnetic field on an automobile radio? Do power

lines show similar magnetic fields? Why do telephone lines have much

weaker magnetic fields?

13. Explain the action of the electric doorbell.

14. Who discovered the principle of electromagnetism?

15. Who invented the telegraph based on the use of electromagnets?

16. Describe a telegraph system based on the use of a compass instead of an electromagnet.

17. Upon what three factors does the strength of an electromagnet depend?

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