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In the following diagram, the position of the needle is shown on the scale of a voltmeter. The least count of the voltmeter and the reading shown by it respectively are :
- 0.15 V and 1.6 V
- 0.05 V and 1.6 V
- 0.15 V and 1.8 V
- 0.05 V and 1.8 V
Here’s how to analyze the figure, calculate the voltmeter reading, and determine the least count:
Understanding Voltmeters
- Scale: Voltmeters have a scale with numbered divisions representing voltage.
- Needle: The needle indicates the voltage being measured.
- Least Count: The smallest measurable voltage difference between two divisions.
Analyzing the Figure
- Numbered Divisions: Look closely at the divisions labeled 0 and 3 in the image.
- Smaller Divisions: Notice that there are smaller divisions between the larger ones. Count how many there are.
- Needle Position: Observe where the needle rests between the smaller divisions.
Calculations
- Least Count:
- Divide the difference between the larger divisions by the number of smaller divisions
- For example, if there are 20 smaller divisions between 0 and 3
- Least Count = (3 – 0) / 20 = 0.15 V
- Voltage Reading:
- Count: Determine how many smaller divisions the needle is past the previous numbered division (e.g., the needle might be past the second division after 1.5).
- Multiply: Multiply this count by the least count.
- Add: Add the product to the value of the previous numbered division.
- For example, if the needle is 2 divisions past 1.5
- Reading = 1.5 + (2 * 0.15) = 1.8 V
Explanation
The correct option is (c), 0.15 V and 1.8 V, if the following aligns with the image’s analysis:
- The smaller divisions between the numbered divisions represent a value of 0.15 V.
- The needle rests two divisions past the 1.5 V mark.
Important Note:
If the number of divisions or the needle’s position is different in the diagram, the calculations will change.
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