An object is placed 15 cm in front of a concave mirror of focal length 10 cm. What is the image distance?
Correct: B
For a concave mirror, according to the New Cartesian Sign Convention, the focal length (f) is negative: f = -10 cm. The object distance (u) is always negative for a real object: u = -15 cm. Using the mirror formula: 1/f = 1/v + 1/u.
1/v = 1/f - 1/u
1/v = 1/(-10) - 1/(-15)
1/v = -1/10 + 1/15
To combine, find a common denominator (30):
1/v = -3/30 + 2/30
1/v = -1/30
v = -30 cm. The negative sign for 'v' indicates that the image is real and formed in front of the mirror.