# Resistors and Resistance MCQs with Answers

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1. Resistance can be described as the:

 A. opposition to current flow
 B. resist rate of the voltage
 C. current acceptability of a voltage
 D. opposition to voltage flow

2. The resistance of a material is most commonly determined by four factors-length, cross-sectional area, type of material and:

 A. voltage
 B. temperature
 C. current
 D. type of supply

3. The resistance of a conductor is proportional to its:

 A. cross-sectional area
 B. area
 C. length
 D. current

4. The resistance of a conductor is inversely proportional to its:

 A. length
 B. the supply voltage
 C. the type of supply
 D. cross-sectional area

5.
The above table gives the resistivity of some common materials used in the electrical industry. The best conductor shown on the table is:

 A. silver
 B. gold
 C. nichrome
 D. copper

6. Resistivity of a material is defined as the:

 A. amount of opposition to a flow of resistance through 1 meter cube of the material
 B. resistance between the opposite faces of a 1 meter cube at a specified temperature
 C. resistance of 100 meters of 1.5 mm2 copper cable at a specified temperature
 D. resistance between two faces of a 1 mm2 block of that material at 20 °C

7. The following formula can be used to determine the resistance of a length of conductor. In the formula the symbol ρ stands for the:

 A. cross-sectional area of the conductor in m2
 B. product of the length of the conductor in meters
 C. resistivity of the material on ohm-meters
 D. resistance of the conductor ohms per meter

8. A copper cable has a length of 450 m and a cross-sectional area of 4.0 mm2. If the resistivity of the copper is 1.72E-8 Ωm, then the resistance of this cable will be:

 A. 193.5 W
 B. 0.105 W
 C. 1.050 W
 D. 1.935 W

9. A 10 Ω resistor is to be made from manganin wire with cross-sectional area of 0.2 mm2. If manganin has a resistivity of 48 E–8 Ωm, then the required length of this size manganin wire will be:

 A. 4.16 W
 B. 41.6 W
 C. 6.25 W
 D. 62.5 W

10. The temperature coefficient of resistance of a material is defined as the change in:

 A. temperature per degree per ohm
 B. resistance per ohm per degree Celsius
 C. cross-sectional area per meter per degree Celsius
 D. length per meter per ohm resistance

11. For some materials, an increase in temperature causes an increase in resistance; these materials are said to have a:

 A. standard temperature coefficient
 B. negative temperature coefficient
 C. positive temperature coefficient
 D. ambient temperature coefficient

12.
The above graph shows the effect of an increase in temperature on a copper conductor. The graph shows that the increase of resistance plotted against temperature is:

 A. non-linear
 B. not predictable
 C. usually 234.5 °C
 D. basically linear

13. The inferred zero formula for determining the resistance of a copper conductor is shown: In the formula, the term t2stands for the:

 A. final temperature of the conductor
 B. initial temperature of the conductor
 C. final resistance of the conductor
 D. initial resistance of the conductor

14. The resistance of a coil of copper wire is 30 Ω at 15ºC. Its resistance at 75ºC will be:

 A. 41.49 W
 B. 37.21 W
 C. 36.64 W
 D. 24.18 W

15. An electric motor has a winding resistance of 15 Ω at 20ºC. After running up to temperature at full load the resistance is measured as 19 Ω. The temperature of the windings will now be:

 A. 17.56°C
 B. 33.57°C
 C. 87.86°C
 D. 94.20°C

16. The temperature coefficient of resistance is defined as the change in:

 A. temperature per degree per ohm resistance
 B. the coefficient of current allowed through a resistance
 C. the resistance of a voltage path per change in current in amperes
 D. resistance per ohm per degree change in temperature

17. The above formula can be used to determine the resistance of a conductor using the temperature coefficient of resistance method. In the formula the term R1 stands for the:

 A. initial resistance of the conductor
 B. final resistance of the conductor
 C. initial temperature of the conductor
 D. final temperature of the conductor

18. If copper conductor has a resistance of 15 Ω at 0ºC, then using the temperature coefficient of resistance method (Note: Consider the temperature coefficient of resistance of copper to be 0.004 27 Ω/Ω/ºC at 0°C.), its resistance at 20ºC will be:

 A. 15.82 W
 B. 16.28 W
 C. 16.60 W
 D. 17.65 W

19. The supply to a 15A air-conditioning unit consists of copper conductors with a cross-sectional area of 2.5 mm2 and a total resistance of 0.38 Ω. When the air-conditioner is operating, the power lost in the conductors will be:

 A. 15 W
 B. 57 W
 C. 85.5 W
 D. 96.5

20. Many materials produce an effect known as ‘superconductivity’ when they are cooled below a certain temperature. At the critical temperature:

 A. electrons cannot pass through the material
 B. the material exhibits a super resistance of a very high ohmic value
 C. all the electrons speed up and reach a super-high temperature
 D. electrons can pass through the material with seemingly zero resistance

21. When current flows through a conductor, the conductor will heat up. If the conductor temperature exceeds the insulation rating of the cable then the:

 A. insulation can be damaged
 B. circuit current will stop
 C. cable will begin to cool
 D. circuit current increase

22. A resistance of 120 Ω is required to carry 200 mA of current. The value of power dissipation required by this resistor is:

 A. 12 W
 B. 4.8 W
 C. 2.4 W
 D. 24 W

23. Smaller value resistors, from 5 watts to several hundred watts, are commonly:

 A. carbon compound type
 B. carbon film type with conductive paint
 C. wire wound on a ceramic former
 D. metal-oxide on a phenolic base

24. The E12 range of preferred values of resistors is based on a tolerance of:

 A. 15%
 B. 20%
 C. 5%
 D. 10%

25.
The size of the above resistor is:

 A. 4k7 W-5%
 B. 4k7 W-10%
 C. 470 W-5%
 D. 470 W-10%

26.
The above diagram shows the characteristic for a typical PTC thermistor. For an increase in temperature, the resistance of the thermistor will:

 A. decrease
 B. increase
 C. remain the same
 D. become unstable

27.
The above diagram shows the characteristic for a typical NTC thermistor. For an increase in temperature between 50°C and 60°C, the resistance of the thermistor:

 A. increases sharply
 B. decreases at the knee point
 C. decreases in an almost linear manner
 D. will be equal to the resistance at 20°C

28. The voltage dependent resistor normally only conducts when the:

 A. circuit current exceeds a certain designed value
 B. power rating of the supply is exceeded
 C. supply voltage needs boosting
 D. supply voltage exceeds a designed limit

29. Light-dependent resistors are used to detect light levels such as in PE (photo-electric) cells on power poles to turn street lights on and off, or to control other night lighting. When light falls on the resistor:

 A. its resistance changes
 B. a voltage is produced
 C. it generates a current
 D. its resistance always remain the same

30. Liquid resistors are often used in motor starters. One advantage of liquid resistance is that the resistance value:

 A. increases as the temperature rises
 B. decreases as the temperature rises
 C. decreases as the temperature decreases
 D. increases as the temperature increases

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