Loaded Voltage Dividers
Replace the divider arm and load by their parallel equivalent before applying voltage division. An ideal voltmeter has infinite resistance and causes no loading.
Why this shows up in the exam
Voltmeter-connected divider circuits · Sensor loading · Battery-network voltage readings
Learn the idea
A device connected across a divider resistor changes that resistor's effective value. A voltmeter or load is another current path, not a passive observer. Unless its resistance is extremely large, it pulls the output voltage away from the unloaded divider value.
🧠 Memory hook: A finite voltmeter joins the circuit and changes it.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- R_lower,eff = R_lower || R_load — loaded lower divider arm
- V_out = V_in R_lower,eff/(R_upper+R_lower,eff) — loaded divider output
How to approach it
- 1Insert the meter resistance in the circuit
- 2Reduce its parallel branch
- 3Apply division to the modified network
Common slip-ups that cost marks
- •Using the unloaded divider formula
- •Putting voltmeter resistance in series
- •Treating a stated finite meter as ideal
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A cell of emf 6 V and internal resistance 1 ohm is connected to a 2 ohm resistor. Find the circuit current.
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