an object is placed in front of aconcave mirror of focal lengt 20cm. the image formed is three times the size of the object. calculate two possible distances of the object from the mirror.
Let the distance of the object from the concave mirror be "x" cm.
According to the mirror formula:
1/f = 1/v + 1/u
where:
f = focal length of the mirror = -20 cm (since it is a concave mirror)
v = distance of the image from the mirror
u = distance of the object from the mirror
Given that the image formed is three times the size of the object, we have:
v/u = -3
Substitute the values into the equation:
1/-20 = 1/(-3x) + 1/x
Multiplying by -20x to simplify the equation:
x = 3x - 20
2x = 20
x = 10 cm
Therefore, the object can be placed at a distance of either 10 cm or -10 cm from the concave mirror.