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B.Tech EEE Circuits and DC Instruments — practice questions — page 2

Explore 46 free Circuits and DC Instruments questions in B.Tech EEE Electrical Engineering. Open each question or exercise to read its content, reference answers and available explanation.

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Circuits and DC Instruments questions and exercises with answers

Showing questions 31–46 of 46.

How must a voltmeter be joined to the device whose voltage is wanted?Read the answer and worked solution →How must an ammeter be joined into the branch whose current is wanted?Read the answer and worked solution →A galvanometer has a current sensitivity of 50 microamperes. What current makes its needle read half scale?Read the answer and worked solution →A galvanometer of 25.0 ohm resistance gives full-scale deflection at 50.0 microamperes. What voltage across it produces that full-scale reading?Read the answer and worked solution →What defines a null measurement?Read the answer and worked solution →How do ordinary meters disturb the circuit they are reading?Read the answer and worked solution →Which null measurement device is used to measure a potential difference?Read the answer and worked solution →Why is a plain voltmeter unable to give the emf of a cell exactly?Read the answer and worked solution →A potentiometer balances at 1.200 ohm of slide wire for an unknown cell, and at 1.247 ohm for a standard cell of 1.600 V. What is the unknown emf?Read the answer and worked solution →Why is the Wheatstone arrangement called a bridge?Read the answer and worked solution →What makes a circuit an RC circuit?Read the answer and worked solution →A 1.00 kilohm resistance charges an 8.00 microfarad capacitor. What is the time constant of the circuit?Read the answer and worked solution →An uncharged capacitor is charged through a resistor from a battery. What fraction of its final voltage does it reach after one time constant?Read the answer and worked solution →A charged capacitor discharges through a resistor. What fraction of its starting voltage is left after one time constant?Read the answer and worked solution →In an RC charging circuit, when is the current largest?Read the answer and worked solution →A defibrillator with a time constant of 8.00 ms starts at 10.0 kV. About how long does it take to fall to roughly 500 V?Read the answer and worked solution →

Worked practice questions

How must a voltmeter be joined to the device whose voltage is wanted?

  1. In parallel with it, so both see one voltage
  2. In series with it, so both carry one current
  3. In parallel with the battery only, never the load
  4. In series with the battery, ahead of the load
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Correct answer: A. In parallel with it, so both see one voltage

1. Objects wired in parallel all sit across the same pair of points, so they share one potential difference. 2. Putting the voltmeter in parallel with a device therefore hands the meter the very voltage being sought. 3. The meter is made with a large resistance so that this extra branch draws almost no current. 4. Wiring it in series would instead give it the branch current, which is what an ammeter is built to read. _Source: OpenStax College Physics (CC BY 4.0), Ch 21 "Circuits and DC Instruments", section 21.4 DC Voltmeters and Ammeters_

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How must an ammeter be joined into the branch whose current is wanted?

  1. In parallel with it, so both see one voltage
  2. In series with it, so both carry one current
  3. In parallel with the battery, across its terminals
  4. In series with the voltmeter already fitted
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Correct answer: B. In series with it, so both carry one current

1. Objects wired in series are met one after the other by the same current. 2. Placing the ammeter in series with a device therefore sends the wanted current through the meter itself. 3. The meter is built with a very small resistance so that adding it barely changes the branch. 4. Wiring it in parallel would place a near short circuit across the device and risk damaging the meter. _Source: OpenStax College Physics (CC BY 4.0), Ch 21 "Circuits and DC Instruments", section 21.4 DC Voltmeters and Ammeters_

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A galvanometer has a current sensitivity of 50 microamperes. What current makes its needle read half scale?

  1. 100 microamperes
  2. 50 microamperes
  3. 12 microamperes
  4. 25 microamperes
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Correct answer: D. 25 microamperes

1. Current sensitivity is the current that swings the needle right to the end of the scale. 2. Here that full-scale current is 50 microamperes. 3. Deflection is proportional to current, so half the deflection needs half the current. 4. Half of 50 microamperes is 25 microamperes. 5. Choosing 100 microamperes would drive the needle past the end of the scale rather than to its middle. _Source: OpenStax College Physics (CC BY 4.0), Ch 21 "Circuits and DC Instruments", section 21.4 DC Voltmeters and Ammeters_

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