An object is placed 1.5 m from a plane mirror. How far is the image from the object?

Analyze the question: An object stands 1.5 m in front of a plane mirror. We need the distance between the object and its image (not the distance from the mirror to the image).

Concept: A plane mirror forms a virtual image that is the same distance behind the mirror as the object is in front of it.

• Object distance = image distance
• u = v

Solution:

• Object distance from mirror = 1.5 m
• Image distance behind mirror = 1.5 m
• Distance from object to image = object distance + image distance

= 1.5 m + 1.5 m = 3.0 m

Answer: A. 3.0 m

Tip: Read the question carefully to see what distance is being asked for. If it asks "how far is the image from the mirror?", the answer is 1.5 m. If it asks "how far is the image from the object?", double it. Examiners love this trap, and options like 1.5 m are often used to catch careless students.