4
1-20. Because its resistance changes very little
with temperature changes, what
conductor is best suited for use in
measuring instruments?
1. Copper
2. Aluminum
3. Manganin
4. Silver
1-21. If a 75-ohm sample of copper wire at 0ºC
is heated to 30ºC, what is the
approximate total resistance? (The
temperature coefficient of resistance of
copper at 0ºC is 0.00427).
1. 0.32 ohm
2. 9.61 ohms
3. 65.39 ohms
4. 84.61 ohms
1-22. What definition best describes an
insulating material?
1. A material that has a very high
resistance
2. A material that has a very low
resistance
3. A material that has a very high
conductivity
4. A material that has a very low
dielectric strength
1-23. The dielectric strength of an insulating
material is a measurement of the
material's ability to resist electrostatic
stress caused by what factor?
1. Resistance
2. Current
3. Voltage
4. Chafing or friction
1-24. Insulation resistance can best be defined
as the ability of an insulating material to
resist what action?
1. Current leakage
2. Electrostatic stress
3. Breakdown by voltage
4. External factors acting upon the
conductor
1-25. For a material to be a good insulator,
what two properties are most important?
1. High dielectric strength and low
insulation resistance
2. High dielectric strength and high
insulation resistance
3. Low dielectric strength and high
insulation resistance
4. Low dielectric strength and low
insulation resistance
1-26. When rubber is used as the insulating
material over a copper conductor, why is
a thin coating of tin used between the
two materials?
1. To decrease the electrostatic stress
2. To increase the insulation resistance
of the rubber
3. To prevent a chemical action from
taking place between the copper and
rubber
4. To reduce the amount of insulating
material required.
1-27. What is the NEC for a rubber heat-
resistance compound?
1. RHH
2. RWH
3. RTW
4. RWT
