"If E = 7.50V and r=0.45Ω, find the minimum value of the voltmeter resistance RV for which the voltmeter reading is within 1.0% of the emf of the battery. Express your answer numerically (in ohms) to at least three significant digits.

The  minimum value is

Explanation:

From the question we are given that

                  The voltage is

                  The internal  resistance is

The objective of this solution is to obtain the minimum value of the voltmeter resistance for which the voltmeter reading is within 1.0% of the emf of the battery

  What is means is that we need to obtain voltmeter resistance such that

                                V = (100% -1%) of E

Where E  is the  e.m.f of the battery and V is the voltmeter reading

                          i.e    V = 99% of E = 0.99 E = 7.425  

Generally

                E = V + ir

     where ir is the internal potential difference of the voltmeter and

                V is the voltmeter reading

 Making i the subject of the formula above

Now the current is constant through out the circuit so,

Where   is the value of voltmeter resistance

                Hence

i already answered it by 34/s

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.