A student accidentally connects a voltmeter in series and an ammeter in parallel with a resistor. Which statement best explains why this arrangement is incorrect?
AA voltmeter in series blocks little current, and an ammeter in parallel measures only resistance
BA voltmeter in series, due to high resistance, can greatly reduce circuit current, while an ammeter in parallel, due to low resistance, may draw excessive current
CBoth instruments have high resistance, so no current flows anywhere
DBoth instruments have low resistance, so the potential difference becomes zero
Answer & Solution
Correct answer: B. A voltmeter in series, due to high resistance, can greatly reduce circuit current, while an ammeter in parallel, due to low resistance, may draw excessive current
The principle is that a voltmeter should have high resistance and be connected in parallel, while an ammeter should have low resistance and be connected in series.
1. If a voltmeter is placed in series, its very high resistance adds a large opposition in the main circuit and can reduce the current drastically.
2. If an ammeter is placed in parallel across a resistor or source, its very low resistance provides an almost direct path for current.
3. That can cause a very large current through the ammeter branch, making the connection unsafe and giving an incorrect measurement.
Option A reverses the effect of high resistance. Option C is wrong because the two instruments do not both have high resistance. Option D is wrong because they do not both have low resistance.
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