Read Real Voltmeters: Redraw the Parallel Branch
This short read prepares one exact NSEP pattern: finite-resistance voltmeter loading. Identify the physical condition before calculating.
Electricity questions depend on identifying charge, a conducting path and the condition that controls current or magnetic effect.
Start with the physical model
Read the configuration once, state the conserved quantity or governing law, and mark any changing geometry, sign convention or limiting condition.
Build the relation
Since the voltmeter reads 3 V from a 9 V supply, R'/(x+R')=1/3, so x=2R'=4r/(r+2). When placed across RB, the reading is 4.5 V, so its parallel equivalent with x must equal 2 MΩ: xr/(x+r)=2.
Check before selecting
Check units, sign and one limiting case. A valid result must still fit the original geometry and stated constraint.
OlympIQ exam lens
- ✓Name the governing law before using a formula.
- ✓Keep the stated geometry and direction information explicit.
- ✓Use one unit or limiting-case check.
An ideal-voltmeter calculation cannot explain different loaded readings across the two resistors.
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