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Questions and Answers
What is the primary function of a resistance box?
What is the primary function of a resistance box?
- To enable selection of various resistances (correct)
- To store electrical energy
- To provide a constant current
- To measure voltage in a circuit
In a rheostat, which terminal is used to achieve variable resistance?
In a rheostat, which terminal is used to achieve variable resistance?
- The fixed and sliding terminals together
- Both fixed terminals
- Only the sliding terminal (correct)
- The middle terminal
When using a milli-ammeter with different ranges, what does selecting a higher range do to the measured current?
When using a milli-ammeter with different ranges, what does selecting a higher range do to the measured current?
- It has no effect on the current reading
- It decreases the sensitivity of the measurement (correct)
- It provides a less accurate measurement
- It always increases the true current reading
What can be inferred about the milli-ammeter readings provided in the example with a 1.0 mA range and a 3.0 mA range?
What can be inferred about the milli-ammeter readings provided in the example with a 1.0 mA range and a 3.0 mA range?
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What is the function of the 'wiper' in a rheostat?
What is the function of the 'wiper' in a rheostat?
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Study Notes
Resistance Box
- Contains multiple resistors that can be activated by inserting keys.
- Resistors are connected between two thick copper conductors for efficient current flow.
- Designed for easy selection of desired resistance values via key operation.
Rheostat
- Functions as a resistance coil to provide variable resistance.
- Features two fixed terminals and one adjustable sliding terminal (wiper).
- Can be utilized solely as a variable resistor using the sliding and one fixed terminal.
- Also serves as a potential divider when fixed terminals are connected to a battery, allowing voltage adjustment through the slider.
Example: Pathfinder Build-28
- A multi-range milli-ammeter constructed with interchangeable shunts and a microampere range galvanometer.
- Measures current in a circuit; for 1.0 mA range selection, it indicates I₁ = 1.0 mA, and for 3.0 mA range, it shows I₂ = 1.5 mA.
- The true current (I₀) in the circuit without the milli-ammeter is calculated by understanding the shunt's impact on current measurement.
- The range increment indicates an increase by a factor of approximately 10³, with the shunt representing the effective resistance seen by the milliammeter.
- Thevenin parameters (In and Rn) across the ammeter are essential for analyzing circuit behavior with different shunt resistances (S₁ for 1 mA and S₂ for 3 mA ranges).
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