# Voltmeter range

We have a voltmeter which in the original set measures voltage to 10V. Calculate the size of the ballast resistor for this voltmeter, if we want to measure the voltage up to 50V. Voltmeter's internal resistance is 2 kiloohm/Volt.

Result

R2 =  80000 Ω

#### Solution:

$U_{ 1 } = 10 \ V \ \\ U_{ 2 } = 50 \ V \ \\ \ \\ R_{ 1 } = 2 \cdot \ 1000 \cdot \ U_{ 1 } = 2 \cdot \ 1000 \cdot \ 10 = 20000 \ Ω \ \\ U_{ 3 } = U_{ 2 }-U_{ 1 } = 50-10 = 40 \ V \ \\ \ \\ I = \dfrac{ U_{ 1 } }{ R_{ 1 } } = \dfrac{ 10 }{ 20000 } = \dfrac{ 1 }{ 2000 } = 0.0005 \ A \ \\ U_{ 3 } = I \cdot \ R_{ 2 } \ \\ \ \\ R_{ 2 } = U_{ 3 }/I = 40/0.0005 = 80000 = 80000 \ \text { Ω }$ Our examples were largely sent or created by pupils and students themselves. Therefore, we would be pleased if you could send us any errors you found, spelling mistakes, or rephasing the example. Thank you!

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