*Question E4B02:
What is the significance of voltmeter sensitivity expressed in ohms per volt?*  

*Correct Answer is  A: The full scale reading of the voltmeter multiplied by its ohms per volt rating is the input impedance of the voltmeter*  

### AI Response: (may contain errors)  

Voltmeter sensitivity expressed in ohms per volt is a measure of how much resistance the voltmeter presents to the circuit per volt of full-scale reading. This is important because it affects the loading of the circuit being measured.

### Explanation of the Correct Answer (A)

- **Correct Answer**: The full scale reading of the voltmeter multiplied by its ohms per volt rating is the input impedance of the voltmeter.
  
  **Why it's correct**:  
  The input impedance of a voltmeter is calculated by multiplying its sensitivity (in ohms per volt) by the full-scale voltage range. This is because the sensitivity tells you how many ohms of resistance the voltmeter has for each volt of measurement range. Therefore, if a voltmeter has a sensitivity of $20,000 \, \text{ohms/volt}$ and a full-scale range of $10 \, \text{V}$, the input impedance is:
  $$ 
  \text{Input Impedance} = 20,000 \, \text{ohms/volt} \times 10 \, \text{V} = 200,000 \, \text{ohms}
  $$

### Why the Other Choices are Incorrect

- **Choice B**: The reading in volts multiplied by the ohms per volt rating will determine the power drawn by the device under test.
  
  **Why it's incorrect**:  
  This choice confuses the concept of input impedance with power calculation. Power drawn by the voltmeter is not directly calculated by multiplying the reading in volts by the ohms per volt rating. Power is calculated using $P = V^2 / R$, where $R$ is the input impedance.

- **Choice C**: The reading in ohms divided by the ohms per volt rating will determine the voltage applied to the circuit.
  
  **Why it's incorrect**:  
  This choice incorrectly suggests a method to determine voltage. The reading in ohms divided by the ohms per volt rating does not provide the voltage applied to the circuit. Voltage is directly measured by the voltmeter.

- **Choice D**: The full scale reading in amps divided by ohms per volt rating will determine the size of shunt needed.
  
  **Why it's incorrect**:  
  This choice is irrelevant to voltmeter sensitivity. Shunt resistors are used in ammeters, not voltmeters, to measure current. The ohms per volt rating does not relate to shunt size.

### Key Takeaway

Understanding voltmeter sensitivity is crucial for ensuring accurate measurements without significantly affecting the circuit under test. Always remember that the input impedance of a voltmeter is a product of its full-scale voltage and its sensitivity in ohms per volt.