Question

A 40 V dc supply is connected to a series combination of two 10 ohm resistors and a variable resistor R.The value of R varies from 0 to 20 ohm .A voltmeter of infinite resistance is connected across 1 of 10 ohm resistors .Which range of values is displayed by voltneter when R is varied. options are A.20v-10vB.30v-10vC.30v-20vD.40v-20v. plz rply fast

Answer 1

(A) 20 V to 10 V

In the problem, the variable rheostat varies from 0 ohm to 20 ohm. Since all the elements in the circuit are linear (they produce a straight V vs I curve), the reading of the voltmeter will also value linearly.

To set the limits of the voltmeter value, we simply must look at voltmeter reading at both extreme conditions of rheostat i.e., o and 20 ohm.

At 0 ohm, the voltmeter reading is 20 V as voltage drop is shared equally between the 10 ohm resistors.

At 20 ohm, the voltmeter reading is 10 V as voltage drop now is divided between 3 elements.

As a result, voltmeter reading varies between 10 and 20 ohm.