Virtual Lab  Thin Lenses
A lens has two focal points, one either side of the lens. The focal length f is the distance between the lens and the focal point.
f is
positive for a converging lens
negative for a diverging lens.
The object distance s is the distance between the lens and the object. s is (nearly) always positive.
The image distance s’ is the distance between the lens and the image.
s’ is
positive if the image is on the other side of the lens from the light source (real)
negative if the image is on the same side of the lens as the light source (virtual)
The thinlens equation relates the object distance and the image distance with the focal length:
Similarly the lateral magnification of the image is given by;
The image formed by a converging lens depends on the position of the object.
The image is described as being
real or virtual
erect or inverted
magnified or diminished



The image screen, showing an in/out of focus image
Measurment  Object Length (cm)  Image Screen Legnth (cm)  
1  
2  
3  
4 