You carried out an experiment to measure the focal length of a converging lens - Leaving Cert Physics - Question 3 - 2005

To find the position of the image formed by the lens, I followed these steps:

1. Adjust the Screen: Move the screen back and forth until a clear image of the object is seen.
2. Check for Parallax: Make sure there’s no parallax error by viewing the crosshairs through the lens and aligning them with the object.
3. Record the Distance: Measure the distance from the lens to the screen, which gives the position of the image.

The key measurements taken during the experiment were:

1. Distance from the object to the lens (u): Measure this from the object (pin) to the lens.
2. Distance from the image to the lens (v): Measure from the lens to the image on the screen.

To calculate the focal length (f) from the measurements, use the lens formula:

$\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$

1. Substitute the measured values of u and v into the equation.
2. Solve for f to find the focal length.

One important precaution taken was to ensure that the crosshairs on the screen were in focus. This was checked several times and adjustments were made to eliminate any possible errors in measurement.