51. What is the effect of heat on the resistances in a Wheatstone bridge?
No effect
Increases the voltage drop across the circuit
Decreases the current flowing through the circuit
Causes a permanent change in the resistance value
Answer.4.Causes a permanent change in the resistance value
Explanation:-
Heating effect: When the current passes through the resistances, due to the heating effect (I2R) the temperature increases. Hence the values of the resistances of the bridge arms change due to the heating effect. The excessively high current may cause a permanent change in the resistance values. This may cause a serious error in the measurement. To avoid this, power dissipation in the arms must calculate well in advance and currents must be limited to a safe value.
52. Which of the following statement is correct about the Wheatstone bridge?
Statement 1:- Resistances less than 1 ohm are difficult to measure accurately. Statement 2:- Resistance greater than 1 megaohm can be accurately measured by Wheatstone.
Both statements are correct
Both Statements are incorrect
Only Statement 1 is correct
Only statement 2 is correct
Answer.3. Only statement 1 is correct
Explanation:-
Resistance values ranging from 1 ohm to 1 megohm can be measured with an accuracy of approximately 0.1%.
However, difficulties are encountered when very high and very low resistances are measured.
Resistances less than 1 ohm is difficult to measure accurately because of uncertainty arising from the contact resistance present between the resistor to be measured and the binding posts of the bridge.
Measurement of resistance greater than 1 megohm becomes difficult because of two factors:
(1) The ratio of standard resistances RA and RB involve a ratio on the order of 1,000 to 1.
(2) The voltage applied to the bridge must be substantially increased to obtain definite galvanometer action.
This results in an increase in the supply voltage thus increasing the power dissipation (heat) of the bridge resistors.
53. Which of the following is/are the applications of the Wheatstone bridge?
Used to measure medium resistance
Used to locate cable fault in telephone line
Used to measure resistance in DC circuits
All of the above
Answer.4. All of the above
Explanation:-
Applications of Wheatstone Bridge
1. The Wheatstone bridge is basically a d.c. bridge and used to measure the medium resistance in the range 1Ω to low megaohm.
2. It is used to measure the D.C. resistance of various types of wire either for the purpose of quality control of the wire itself or of some assembly in which it is used.
3. It is used by telephone companies to locate cable faults. The fault may be two lines shorted together, or a single line shorted to the ground. If there is a fault on the cables, the Wheatstone bridge can be used to find the location of the fault by using the known resistance per meter of the cables.
4. It is used for the Measurement of the resistance of motor windings, transformers, solenoids, and relay coils.
54. How can a Wheatstone bridge be used for the measurement of physical parameters?
In conjunction with a rectifier
Along with an op-amp
By connecting it to a thermistor
By making use of a transducer
Answer.4. By making use of a transducer
Explanation:-
An unbalanced bridge condition occurs when is not equal to zero. The unbalanced bridge is used to measure several types of physical quantities such as mechanical strain, temperature, or pressure. This can be done by connecting a transducer in one leg of the bridge, as shown in Figure.
The resistance of the transducer changes proportionally to the changes in the parameter that it is measuring. If the bridge is balanced at a known point, then the amount of deviation from the balanced condition, as indicated by the output voltage, indicates the amount of change in the parameter being measured. Therefore, the value of the parameter being measured can be determined by the amount that the bridge is unbalanced.
55. The types of faults in a telephone line are ______
Line to line or line to ground
Triple line to line or line to ground
Open circuit and short circuit
Symmetrical and unsymmetrical
Answer.1. Line to Line or Line to ground
Explanation:-
In a telephone line, line to line and line to ground faults occur. Symmetrical, unsymmetrical, open circuit, short circuit, triple line to line, and line to ground faults occur in power systems.
56. Telephone companies make use of the Wheatstone bridge for ________
Measuring the telephone resistance
Computing the line strength
Maintaining Dialtone
Locating the cable faults
Answer.4. Locating the cable faults
Explanation:-
The cable repairman’s test set is used to pinpoint the location of telephone cable faults after the approximate location of the fault has been obtained by the use of the Wheatstone bridge. The test set can be used to locate shorts, grounds cross, split pairs, wet spots, and similar troubles in a cable. It can’t be used to locate Open-circuit.
The test set includes a tone unit, an exploring coil equipped with three jacks, and a telephone receiver equipped with a cord and plug for connection to the exploring coil packs and Wheatstone Bridge. Telephonic resistances are determined using suitable techniques
57. Thermal compensation can be provided in a Wheatstone bridge by _______
Making use of a heat sink
Dual element gauge
Using cooling fans
Immersing the circuit into a liquid
Answer.2. Dual element gauge
Explanation:-
Compensation of the temperature effect in a bridged network is accomplished by putting dissimilar gages into adjacent bridge arms.
The gage in the first arm should have a relatively small temperature effect with respect to the gage factor. The gage in the second arm should have a high-temperature effect in the same direction. With proper, fixed series and shunt resistances for the gage in the second arm, it is possible to obtain an overall temperature effect for the second arm that is equal to that of the first arm. Hence, the temperature effects of the two arms will cancel each other.
The active gauges are connected in opposite arms of the Wheatstone bridge so that the contribution of each to the output could be expressed as a sum. Under a positive strain (tension) will increase in length and decrease in diameter, resulting in an increase in resistance. A compressive force will decrease the wire length, increase the diameter, and Lower the resistance.
Dual element gauges are also employed (one having positive and the other negative response to temperature changes) will cancel out each other’s effects within a set temperature range.
The most frequently employed method is the use of dummy elements. The dummy gauge is mounted on the same surfaces as the active element, and is exposed to the same temperature, but is not subject to the forces applied. If such a dummy is connected in a Wheatstone bridge arm adjacent to the active element, it will automatically compensate for temperature effects.
58. Wheatstone bridge is a _______
A.C bridge
D.C bridge
High voltage bridge
Power dissipation bridge
Answer.2. D.C bridge
Explanation:-
DC bridges are used to determine the unknown conducting value or sometimes to determine the conductance associated with conducting wires. Wheatstone bridge and Kelvin double bridge are the two types in this category.
59. Wheatstone bridge is used to measure the d.c. resistance of various types of wires for _________
Determining their effective resistance
Computing the power dissipation
Quality control of wire
Maintaining a source of constant e.m.f
Answer.3. Quality control of wire
Explanation:-
Wheatstone bridge is used to measure the D.C. resistance of various types of wire either for the purpose of quality control of the wire itself or of some assembly in which it is used.
60. By using the variations on a Wheatstone bridge we can ______
Measure quantities such as voltage, current, and power
Measure high resistance values
Measure quantities such as complex power
Measure quantities such as capacitance, inductance, and impedance
Answer.4. Measure quantities such as capacitance, inductance, and impedance
Explanation:-
The most commonly used techniques for the measurement of Resistance, inductance, capacitance quantities are those of bridge measurement. The word “bridge” refers to the fact that in such measurements two points in the circuit are bridged by a detector that detects either a potential difference or a null between them. They provide an accurate method of measuring resistance, inductance, and capacitance values and enable the detection of very small changes in these quantities about a nominal value. They are of immense importance in measurement system technology because so many transducers measuring physical quantities have an output that is expressed as a change in resistance, inductance, or capacitance.
A Wheatstone bridge consists of resistive arms. It is used for the measurement of quantities such as capacitance, inductance, and impedance by making use of the variations such as Wien’s bridge because the ratio can be applied to these quantities as well.
