measurement of the focal length of a convex lens

Question 1

how did the student find an approximate value for the focal length of the lens?

Answer 1

focus a distant object onto a screen using the lens. measure the distance between the lens and the screen for the approx. focal length

Question 2

what was the advantage of finding the approximate value of the focal lens

Answer 2

allows you to set up the experiment with the object outside the focal length{gives a real image}

Question 3

describe, with reference to the diagram, how the student found the position of the image.

Answer 3

set up as shown in the diagram move the screen until the clearest sharpest image of the object is projected onto the screen. measure the distance from the lens to the screen to find the image distance

Question 4

why is it difficult to measure the image distance accurately?

Answer 4

you must ensure that the clearest sharpest image is found, which can be difficult to determine, and avoid parallax error when reading the ruler

Question 5

what formula is used to calculate the focal length

Answer 5

1/f=1/u+1/v

Question 6

why is it difficult to measure the image distance when the object distance is less than 10cm?

Answer 6

object is more likely to be inside the focal length-a virtual image cannot be found on a screen.

Question 7

give two sources of error in measuring the image distance and state how one of these errors can be reduced.

Answer 7

avoid parallax error
measure from the centre of lens
find the clearest sharpest image

Question 8

what is plotted on the x and y axes for the graph for this experiment?

Answer 8

calculate values of 1/u and 1/v. plot these points on a graph and draw a best line