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Questions and Answers
What classification do resistances of the order of 1 Q and under fall into?
What classification do resistances of the order of 1 Q and under fall into?
Which of the following methods is NOT used for measuring medium resistances?
Which of the following methods is NOT used for measuring medium resistances?
What do high resistances classify as?
What do high resistances classify as?
What is a common limitation of the ammeter-voltmeter method?
What is a common limitation of the ammeter-voltmeter method?
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Which resistance measurement technique is generally suitable for laboratory use due to instrument availability?
Which resistance measurement technique is generally suitable for laboratory use due to instrument availability?
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What range of resistances does the medium resistance classification cover?
What range of resistances does the medium resistance classification cover?
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What can lead to inaccurate results when measuring resistance?
What can lead to inaccurate results when measuring resistance?
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What is the primary purpose of the Carey-Foster Slide-wire Bridge?
What is the primary purpose of the Carey-Foster Slide-wire Bridge?
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What does the symbol 'l2' represent in the context of the slide-wire bridge?
What does the symbol 'l2' represent in the context of the slide-wire bridge?
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Which equation relates the resistances S and R to the lengths of the slide-wire at balance?
Which equation relates the resistances S and R to the lengths of the slide-wire at balance?
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How are the resistances P and Q adjusted in relation to R and S?
How are the resistances P and Q adjusted in relation to R and S?
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What is eliminated from the calculations when comparing resistances S and R using the Carey-Foster Slide-wire Bridge?
What is eliminated from the calculations when comparing resistances S and R using the Carey-Foster Slide-wire Bridge?
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What is the calculated true value of resistance R based on the measurement Rm2?
What is the calculated true value of resistance R based on the measurement Rm2?
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What is the percentage error associated with the ammeter reading at 0.42 A?
What is the percentage error associated with the ammeter reading at 0.42 A?
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How is the error due to both the ammeter and voltmeter calculated?
How is the error due to both the ammeter and voltmeter calculated?
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What is the formula used to calculate the percentage error in the voltmeter reading of 35.5 V?
What is the formula used to calculate the percentage error in the voltmeter reading of 35.5 V?
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What does the connecting diagram for the substitution method include?
What does the connecting diagram for the substitution method include?
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What is the formula used to determine the percentage error from the voltmeter?
What is the formula used to determine the percentage error from the voltmeter?
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What is the percentage error calculated by combining the ammeter error of 1.19% and voltmeter error of 0.704%?
What is the percentage error calculated by combining the ammeter error of 1.19% and voltmeter error of 0.704%?
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Which value is not directly derived from the measured values of resistance in the calculations?
Which value is not directly derived from the measured values of resistance in the calculations?
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What happens when the switch is toggled to position '2' in the substitution method?
What happens when the switch is toggled to position '2' in the substitution method?
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What is the typical accuracy range for measurements using an ordinary ohmmeter?
What is the typical accuracy range for measurements using an ordinary ohmmeter?
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What condition must be satisfied for a Wheatstone bridge to be considered balanced?
What condition must be satisfied for a Wheatstone bridge to be considered balanced?
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Which component is typically used as a null detector in a Wheatstone bridge?
Which component is typically used as a null detector in a Wheatstone bridge?
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What is the role of the standard resistor in the substitution method?
What is the role of the standard resistor in the substitution method?
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How does the deflection of the galvanometer relate to the total resistance in the circuit?
How does the deflection of the galvanometer relate to the total resistance in the circuit?
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In the Wheatstone bridge method, which factors influence the accuracy of measurement?
In the Wheatstone bridge method, which factors influence the accuracy of measurement?
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Which of these is a characteristic of the substitution principle used in resistance measurement?
Which of these is a characteristic of the substitution principle used in resistance measurement?
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Which parameters primarily affect the measurement accuracy in resistance measurements?
Which parameters primarily affect the measurement accuracy in resistance measurements?
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When measuring high resistances, which method is commonly used instead of the standard Wheatstone bridge configuration?
When measuring high resistances, which method is commonly used instead of the standard Wheatstone bridge configuration?
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What is the key relationship described in the formula for bridge balance, $P=I_2R$?
What is the key relationship described in the formula for bridge balance, $P=I_2R$?
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What happens to the sensitivity of a bridge circuit if the ratio P/Q is greater or smaller than unity?
What happens to the sensitivity of a bridge circuit if the ratio P/Q is greater or smaller than unity?
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In the Thevenin equivalent circuit, what parameters are represented in the circuit?
In the Thevenin equivalent circuit, what parameters are represented in the circuit?
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For a bridge with equal arms, what is the relationship between R, S, P, and Q?
For a bridge with equal arms, what is the relationship between R, S, P, and Q?
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What is the effect of averaging two readings in a galvanometer circuit?
What is the effect of averaging two readings in a galvanometer circuit?
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What does the current through the galvanometer depend on?
What does the current through the galvanometer depend on?
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What is the effect of having a low ratio P/Q in the sensitivity of a circuit?
What is the effect of having a low ratio P/Q in the sensitivity of a circuit?
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What expression relates to finding the Thevenin or open circuit voltage in a galvanometer circuit?
What expression relates to finding the Thevenin or open circuit voltage in a galvanometer circuit?
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What can be inferred about the relationship between sensitivity and accuracy in bridge circuits?
What can be inferred about the relationship between sensitivity and accuracy in bridge circuits?
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What role does the resistance of the galvanometer circuit, denoted by G, play in the measurements?
What role does the resistance of the galvanometer circuit, denoted by G, play in the measurements?
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If the ratio of P/Q is found to be 1000, how does it compare to unity in terms of sensitivity?
If the ratio of P/Q is found to be 1000, how does it compare to unity in terms of sensitivity?
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Study Notes
Measurement of Resistance
- Low resistances are those of 1 Ω or less.
- Medium resistances range from 1 Ω to 0.1 MΩ.
- High resistances are above 0.1 MΩ.
- Different measurement techniques are used for each class.
Measurement of Medium Resistances
-
Ammeter-Voltmeter Method:
- Used for measuring medium resistances.
- Two types of connections shown (Fig. 14.1(a) and 14.1(b)).
- Accurate measurements require ammeter resistance to be zero and voltmeter resistance to be infinite.
- In reality, these ideal conditions are not met
- Measured resistance is higher than true resistance because of ammeter resistance.
- Measured value = True value + Ammeter resistance.
- Relative error is equal to (Measured - True)/True).
- This method is popular in labs because these instruments are available.
-
Substitution Method:
- More accurate than the ammeter-voltmeter method.
- Errors are reduced by keeping the battery emf constant.
-
Wheatstone Bridge Method:
- A very important instrument extensively used.
- Measures resistances to high accuracy.
- It utilizes a null indication principle.
-
Ohmmeter Method
- Not explained in detail.
Additional Notes
- Accuracy of measurements is affected by the resistance of the measuring instruments.
- Errors are minimized when the resistance being measured is significantly larger than the instrumentation resistance.
- The suitability of a method depends on the values of resistance under measurement and the instrument resistances.
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