3.7 Resistance/Resistor.

44. If a resistor is too small or misshapen to fit the colour code bands, how else is it's value indicated?. Option A. Dots. Option B. Number code. Option C. Letter code.

Correct Answer is. Letter code. Explanation. NIL.

14. The formula for resistance in series is. Option A. RT = R1 + R2 + R3 .....Rn. Option B. RT = R1 * R2 * R3 .....Rn. Option C. 1/RT = 1/( R1 * R2 * R3 .....Rn).

Correct Answer is. RT = R1 + R2 + R3 .....Rn. Explanation. NIL.

10. In a Wheatstone Bridge, the ammeter reads zero, and the variable resistor is adjusted to 5 ohms. Resistor P has a value of 10 ohms and Q has a value of 100 ohms. What is the value of the unknown resistor?. Option A. 5 ohms. Option B. 0.5 ohms. Option C. 50 ohms.

Correct Answer is. 0.5 ohms. Explanation. R = Rv * P/Q.

15. What is the combined value of resistances of 4 ohm and 6 ohm connected in parallel?. Option A. 0.24 ohm. Option B. 2.4 ohm. Option C. 24 ohm.

Correct Answer is. 2.4 ohm. Explanation. Resistors in parallel, the total resistance will be less than the smallest (but only slightly less).

3. A resistor has 4 bands on it coloured blue, yellow, yellow, gold. It's value is. Option A. 640 kΩ ± 5%. Option B. 6.4 mΩ ± 10%. Option C. 64 kΩ ± 5%.

Correct Answer is. 640 kΩ ± 5%. Explanation. NIL.

2. Resistance is measured using what unit of temperature?. Option A. Absolute. Option B. Centigrade. Option C. Fahrenheit.

Correct Answer is. Absolute. Explanation. NIL.

46. This is a diagram of a. Option A. Variable Voltage source. Option B. Variable Current source. Option C. Variable Resistor.

Correct Answer is. Variable Resistor. Explanation. A potentiometer is not a voltage or current 'source'.

48. A thyristor. Option A. if energized on, will switch on a circuit. Option B. has a positive temperature coefficient. Option C. if energized on, will switch off a circuit.

Correct Answer is. if energized on, will switch on a circuit. Explanation. An SCR is an example of a thyristor.

4. The electron flow through a conductor will be decreased the most if the cross sectional area. Option A. is decreased and the length is increased. Option B. and the length are both decreased. Option C. and the length are both increased.

Correct Answer is. is decreased and the length is increased. Explanation. NIL.

40. Carbon has a. Option A. temperature coefficient of zero. Option B. positive temperature coefficient. Option C. negative temperature coefficient.

Correct Answer is. negative temperature coefficient. Explanation. Carbon is a semiconductor, so its resistance reduces with temperature.

31. The unit for resistivity is the. Option A. ohms/square meter. Option B. ohms/meter. Option C. ohm.meter.

Correct Answer is. ohm.meter. Explanation. NIL.

23. A 300 ohm resistor would have a colour code of. Option A. orange, brown, black. Option B. orange, orange, brown. Option C. orange, black brown.

Correct Answer is. orange, black brown. Explanation. NIL.

7. If the resistance of a resistor which is in series with two other resistors is doubled. Option A. the current in that resistance is doubled. Option B. the volts drop across that resistor increases. Option C. the current in that resistance is halved.

Correct Answer is. the volts drop across that resistor increases. Explanation. The current will reduce, but not halved, since it depends on how big the other two resistors are in relation to it. It will however take a greater share of the voltage drop in the circuit.

6. Total resistance in a parallel resistor circuit, of R1 and R2 is. Option A. RT = 1/R1 + 1/R2. Option B. 1/RT = (R1 * R2) ÷ (R1 + R2). Option C. 1/RT = 1/R1 + 1/R2.

Correct Answer is. 1/RT = 1/R1 + 1/R2. Explanation. NIL.

27. Conductance of a circuit is 2 milliMhos. What is its resistance?. Option A. 5000 Ohms. Option B. 500 Ohms. Option C. 5 Megohms.

Answer is. 500 Ohms. Explanation. Conductance is the ease at which current flows. It is the inverse of resistance. (The unit 'Mho' is 'Ohm' backwards). Conductance = 2/1000 Mhos. Therefore Resistance = 1000/2 Ohms.

12. Six resistors each of 6 ohms would be. Option A. 1 ohm in series. Option B. 1 ohm in parallel. Option C. 36 ohms in parallel.

Correct Answer is. 1 ohm in parallel. Explanation. Get the formulas for resistors in parallel and resistors in series. Or, remember that resistors in series, total is greater than the largest,and resistors in parallel, total is less than the smallest.

22. The bridge circuit shown will be balanced when the value of the unknown resistor R is. Option A. 2 ohms. Option B. 18 ohms. Option C. 14 ohms.

Correct Answer is. 2 ohms. Explanation. 72 / 24 = 6 / R, R = 2 ohms.

29. A 2 Megohm resistor can be written. Option A. 2M0F. Option B. 20MF. Option C. M20F.

Correct Answer is. 2M0F. Explanation. Sometimes the multiplier, like M (for meg), or K (for kilo) or R (for 1) is put in place of the decimal point. The last letter is the tolerance. See Forum for more info.

8. The total resistance of the circuit shown is. Option A. 3 Ohms. Option B. 1.33 Ohms. Option C. 12 Ohms.

Correct Answer is. 3 Ohms. Explanation. Series 3 + 3 = 6 ohms. Then, two 6 ohm resistors in parallel, total is half = 3 ohms.

36. A potentiometer has which of the following properties?. Option A. Wire wound. Option B. 3 terminals. Option C. Preset values.

Correct Answer is. 3 terminals. Explanation. NIL.

34. The unknown resistance R in the Wheatstone bridge shown is. Option A. 4 ohms. Option B. 16 ohms. Option C. 1 ohm.

Correct Answer is. 4 ohms. Explanation. R = 2 * 8/4. Read up on Wheatstone bridges.

20. If 2 resistors, one red, yellow, black, gold and the other violet, blue, black, silver were replaced by a single resistor. Ignoring tolerance, what would the colour coding be?. Option A. Brown, black, brown. Option B. Black, brown, black. Option C. Brown, black, black.

Correct Answer is. Brown, black, brown. Explanation. The red/yellow/black resistor is 24 ohms (get a colour code chart). The violet/blue/black resistor is 76 ohms. Total is 100 ohms. A 100 ohm resistor is brown/black/brown.

49. The temperature of a pure metal can greatly affect the resistance of it. What temperature scale is used?. Option A. Absolute. Option B. Centigrade. Option C. Fahrenheit.

Correct Answer is. Centigrade. Explanation. NIL.

19. Which of these will cause the resistance of a conductor to decrease?. Option A. Decrease the length or the cross-sectional area. Option B. Increase the length or decrease the cross-sectional area. Option C. Decrease the length or increase the cross-sectional area.

Correct Answer is. Decrease the length or increase the cross-sectional area. Explanation. Get the formula for resistance of a conductor.

26. Five different value resistors all have the same voltage dropped across them. How are the resistors connected?. Option A. In Series/Parallel. Option B. In Series. Option C. In Parallel.

Correct Answer is. In Parallel. Explanation. Resistors in parallel with each other all have the same voltage drop.

39. What happens to the resistance of a copper conductor when the temperature increases?. Option A. It decreases. Option B. It increases. Option C. It remains the same.

Correct Answer is. It increases. Explanation. All materials excepts semiconductors have a positive temperature coefficient.

45. This is a diagram of a. LDR Option A. Light Dependant Resistor. Option B. Laser Diode Rectifier. Option C. Logarithmic Differential Resistor.

Correct Answer is. Light Dependant Resistor. Explanation. NIL.

43. What is represented by this diagram?. Option A. Thermistor. Option B. Rheostat. Option C. Potentiometer.

Correct Answer is. Potentiometer. Explanation. A potentiometer has 3 connections, a rheostat has only 2.

24. In this circuit, Rx is equal to. Option A. R2 * R4 ÷ R3. Option B. R3 * R4 ÷ R2. Option C. R3 * R2 ÷ R4.

Correct Answer is. R3 * R2 ÷ R4. Explanation. Assuming the diagram is incomplete (no cross branch with a zeroed ammeter as per a Wheatstone bridge) Take Rx/R3 = R2/R4 and transpose.

47. Resistors required to carry a comparatively high current and dissipate high power are usually of. Option A. Wire wound metal type. Option B. Carbon compound type. Option C. Wire wound ceramic type.

Correct Answer is. Wire wound ceramic type. Explanation. Aircraft Electricity and Electronics by Eismin, Chapter 6, pg 101.

32. A 47 Kilohm resistor with a 10% tolerance has the following colour code:. Option A. Yellow, Violet, Orange, Silver. Option B. Orange, Violet, Red, Gold. Option C. Red, Orange, Yellow, Silver.

Correct Answer is. Yellow, Violet, Orange, Silver. Explanation. Aircraft Electricity and Electronics Eismin Page 100.

21. A 47 kilohm resistor has the following colour code:. Option A. Yellow, Violet, Orange. Option B. Red, Orange, Yellow. Option C. Orange, Violet, Red.

Correct Answer is. Yellow, Violet, Orange. Explanation. NIL.

5. Small resistors too small or mis-shapen for the application of colour are marked instead using. Option A. an abbreviated resistance value. Option B. a letter code. Option C. a dot code.

Correct Answer is. a letter code. Explanation. NIL.

35. This is a symbol for. Option A. a visual display rectifier. Option B. a variable differential resistor. Option C. a voltage dependant resistor.

Correct Answer is. a voltage dependant resistor. Explanation. VDR = Voltage Dependant Resistor.

30. In a Wheatstone bridge at balance the galvanometer reads zero. Option A. amps. Option B. ohms. Option C. volts.

Correct Answer is. amps. Explanation. NIL.

37. An increase in operating temperature in most electrical devices carrying current results in. Option A. a decrease in resistance and an increase in current. Option B. no effect on the resistance and current. Option C. an increase in resistance and a decrease in current.

Correct Answer is. an increase in resistance and a decrease in current. Explanation. Most conductors have a 'positive temperature coefficient'. The exceptions are semiconductors.

28. When light hits a photodiode, its resistance. Option A. stays the same. Option B. increases. Option C. decreases.

Correct Answer is. decreases. Explanation. Resistance decreases with light intensity.

11. In general, increasing the cross sectional area of an electrical cable. Option A. increases its resistance. Option B. enables it to carry more voltage. Option C. enables it to carry more current.

Correct Answer is. enables it to carry more current. Explanation. Get the formula for resistance of a cable. If you increase the cross sectional area, its resistance will decrease and it can carry more current. 'Carrying voltage' is not technically correct terminology, and besides, Any size cable can 'carry' any size voltage, but it is the current which will destroy it.

42. If the temperature of a pure metal is reduced to absolute zero, its resistance will be. Option A. unaffected. Option B. practically zero. Option C. infinity.

Correct Answer is. practically zero. Explanation. NIL.

33. The total resistance in a circuit is greater than the least resistor. This is true for a. Option A. series and parallel circuit. Option B. series circuit only. Option C. parallel circuit only.

Correct Answer is. series circuit only. Explanation. NIL.

16. If a number of resistors are connected in parallel, the total resistance is. Option A. smaller than the lowest. Option B. the same as the lowest. Option C. greater than the lowest.

Correct Answer is. smaller than the lowest. Explanation. Resistors in parallel. Total resistance is smaller than the lowest single resistor.

17. The resistance to electrical flow in a wire depends on. Option A. the diameter, length, material of wire and temperature. Option B. the material only - copper or aluminium. Option C. the length and material of the wire only.

Correct Answer is. the diameter, length, material of wire and temperature. Explanation. Get the formula for resistance of a conductor, and don't forget that most materials have a positive temperature coefficient.

1. The resistance of a material is. Option A. independent of the material type. Option B. the same as its conductance. Option C. the reciprocal of its conductance.

Correct Answer is. the reciprocal of its conductance. Explanation. NIL.

18. When resistors are in parallel the total current is equal to. Option A. the current through one resistor. Option B. the sum of the currents. Option C. the reciprocal of all the currents.

Correct Answer is. the sum of the currents. Explanation. NIL.

25. In a parallel circuit containing resistors. Option A. the sum of the voltage drops equals applied voltage. Option B. the voltage is the same in all parts of the circuit. Option C. resistance is determined by value of current flow.

Correct Answer is. the voltage is the same in all parts of the circuit. Explanation. In a parallel circuit, the voltage across each resistor is the same.

41. The 5th coloured band on a resistor represents the. Option A. reliability or temperature coefficient. Option B. tolerance. Option C. multiplier.

Correct Answer is. tolerance. Explanation. NIL.

9. Potentiometers are used as a. Option A. variable voltage source. Option B. variable resistor. Option C. variable current source.

Correct Answer is. variable resistor. Explanation. Potentiometers are not a 'source' of voltage.

13. A potentiometer varies. Option A. resistance. Option B. current. Option C. voltage.

Correct Answer is. voltage. Explanation. A potentiometer is basically a variable voltage splitter.

38. Copper is an inferior conductor to aluminium when comparing. Option A. CSA with CSA. Option B. weight for weight. Option C. load for load.

Correct Answer is. weight for weight. Explanation. Copper is a better inductor but aluminium is much lighter. CSA = cross sectional area (not Child Support Agency).