Page 336 - NS-2 Textbook

PHYSICAL SCIENCE 331

through the circuit. Using P as the symbol for electrical 8. What are the six common methods of producing
power, the basic power formula is: P ~ IE (Equation D). voltage?
As an example, when E is 2 volts and ] is 2 amperes, P be- 9. What is a thermocouple?
comes 4 watts. 10. Where is the photoelectric cell used?
When voltage is doubled and resistance remains 11. What is the most common source of chemically cre-
unchanged, power is doubled twice. This occurs be- ated electricity?
cause the doubling of voltage causes a doubling of cur- 12. What is the uuit of measure for current?
rent (see Equation A), which therefore doubles both of 13. What is the unit of measure for resistance?
the factors that determine power. In other words, the 14. What factors determine the amotmt of resistance in a
rate of change of pOVller, in a circuit of fixed resistance, conductor?
is the square of the change in voltage. Thus the basic 15. What is an electrical circuit?
power formula P ~ IE may also be expressed as P ~ E2/R 16. How does electricity flow in a circuit?
(Equation E), or P ~ ]2R (Equation F). (These equations 17. What is a schematic diagram?
can easily be derived by simple substitution from Equa- 18. A. Describe Ohm's law.
tions A and B.) .. B. What does it enable us to find?
19. What is the uuit of measure for power?
20. What are the three formulas for electrical power?
CRITICAL THINKING
Simple Circuit Problems
1. List some basic safety precautions one should observe
1. A simple circuit consists of one 60-watt bulb and a
when working with any type of electrical equipment
standard 120-volt source of electricity.
or circuitry.
A. What is the current I in amperes?
2. Analogies are often drawn between the way in which
B. What is the resistance R in ohms?
water flows downhill and through pipes and the way
2. A simple circuit powered by a 115-volt battery has
electricity is generated and travels through wires and
200 ohms of resistance in it. What is the current I in
resistances. Describe some of these analogies and
amperes?
how they can be used to help understand how elec-
3. A simple battery-powered circuit has .75 ampere run-
tricity works.
ning through one ISO-ohm resistor. Using this infor-
3. List the various energy transformations that take place
mation, find the voltage of the battery.
in a conventional power distribution network from the
time that a fossil fuel is burned to provide energy in
Power Problems
the generating plant until the electrical power is con-
sumed in a person's horne. 1. What power in watts is being dissipated in a resis-
tance of 100 ohms if 2 amperes of current are flowing
through it?
Study Guide Questions 2. What is the resistance of a 100-watt light bulb con-
nected to a 120-volt power supply?
1. What are the positive and negative charged particles
in an atom?
Vocabulary
2. What force keeps the electrons of an atom revolving
in regular orbits? electricity battelY
3. How is electricity conveyed? conductor schematic
4. A. What substances are the best conductors of elec- insulator Ohm's law
tricity? electromotive force ohm
B. Why? voltage resistance
5. What is an insulator? thermocouple ampere
6. What is the fWldamental law concerning electrical photoelectric current
charges? voltmeter ammeter
7. Y'lhat unit is used to measure electromotive force? ohmmeter