Ray Tracing and Lens Formula for Image Location

[anotherperson]

Homework Statement

An object is locted 15cm infront of a convae lends with a focal length of 10cm. use ray tracing to determine the location of the image. try to draw to scale

i)is the image upright or inverted?
ii)is the image real or virtual?
iii)use your ray-tracing diagram to determine the distance from the lens to the image and label your diagram with this value
iv)now calculate this lens to image distance using the thing lens formula
v) determine the linear magnification of the image relative to the object

Homework Equations

1/p+1/q=1/f
m=-q/p

The Attempt at a Solution

the image will be upright and virtual. and i was able to do the ray tracing diagram

for part iii) I am unsure which equation to use as if i use the lens formula i get the wrong answer,
1/15+1/q=1/10

and hense the wrong answer for part iv)

i'm able to work out v if i have the answer for iv. as m=-q/p which will be m=-answer/15

 

[yoshtov]

remember that for concave lenses, focal length is negative. try (-1/10cm) instead of (1/10cm).

 

[rl.bhat]

Use proper sign convention.
What change you have to make in the lens formula when you are using concave and convex lens?

 

[anotherperson]

i still get the wrong answer if i do
1/15+1/q=-1/10

 

[rl.bhat]

What is your answer ?

 

[anotherperson]

ohhh no it is right
-6 meaning its 6cm away and then the next part it is also 6cm making my magnification 0.4. is that correct?

 

[yoshtov]

my equations show the same result, so i say yes.

 

[anotherperson]

thanks!