Calculating Magnification of Christmas Tree Ornament

[Kris1120]

Homework Statement

A spherical Christmas tree ornament is
4.76 cm in diameter.
What is the magnification of the image of
an object placed 11.9 cm away from the ornament?

Homework Equations

f = .5* r

(1/di) + (1/do) = 1/f

m=-(di/do)

The Attempt at a Solution

f = .5*2.38 = 1.19 cm

(1/di) = (1/1.19) - (1/11.9) = 1.32222 cm

m =-(1.32222/11.9) = -0.1111

 

[alphysicist]

Hi Kris1120,

Homework Statement

A spherical Christmas tree ornament is
4.76 cm in diameter.
What is the magnification of the image of
an object placed 11.9 cm away from the ornament?

Homework Equations

f = .5* r

(1/di) + (1/do) = 1/f

m=-(di/do)

The Attempt at a Solution

f = .5*2.38 = 1.19 cm

I don't believe this is right. What type of mirror is this? What does that tell you about the focal length?