Question

2 resistors of resistance 1000 ohm and 2000 ohm are joined in series with a 100V supply. A voltmeter of internal resistance 4000 ohm is connected to measure the potential difference across 1000 ohm resistor. Calculate the reading shown by the voltmeter.

Answer 1

The voltmeter reading will be 35.7 volt

Explanation:

The resistor 1000 ohm and 4000 ohm are connected in parallel .

Their combined resistance is supposed R₁

Thus $\frac{1}{R_1}$ = $\frac{1}{1000}$ + $\frac{1}{4000}$  

or R₁ = 800 ohm

Therefore the total resistance in circuit is = 2000 + 800 = 2800 ohm

Because these are in series .

We can find  current flowing through the circuit  I = $\frac{V}{R}$ = $\frac{100}{2800}$ = $\frac{1}{28}$

here R is total resistance .

The potential difference across 1000 ohm = $\frac{1}{28}$ x 1000 = 35.7 volt

Thus voltmeter reading will be 35.7 volt