error due to imperfect graduations
error due to eccentricity of verniers
error due to imperfect adjustment of plate levels
error due to line of collimation not being perpendicular to horizontal axis
Answer is Right!
Answer is Wrong!
The correct answer is: D. error due to line of collimation not being perpendicular to horizontal axis.
The line of collimation is the line of sight of the telescope. It should be perpendicular to the horizontal axis of the telescope in order to ensure accurate readings. If the line of collimation is not perpendicular, then the readings will be off.
Taking the mean of both face observations will eliminate the error due to line of collimation because the error will cancel out. This is because the error will be in the same direction for both face observations, but in opposite directions for the two readings. When the mean is taken, the error will cancel out.
The other options are not eliminated by taking the mean of both face observations.
- Error due to imperfect graduations: This error is caused by the graduations on the telescope being inaccurate. Taking the mean of both face observations will not eliminate this error.
- Error due to eccentricity of verniers: This error is caused by the vernier scale not being perfectly aligned with the main scale. Taking the mean of both face observations will not eliminate this error.
- Error due to imperfect adjustment of plate levels: This error is caused by the plate levels not being perfectly adjusted. Taking the mean of both face observations will not eliminate this error.