Solved Examples

Example 1:  

A student stands 3.0 meters in front of a large plane mirror. She then walks 1.0 meters towards the mirror. What is the new distance between the student and her image? 

Step 1: Find the new position

• Original distance: 3.0 m.

• She walks closer by 1.0 m.

• New Object Distance (do​) = 2.0 m.

Step 2: Apply the Rule

• In a plane mirror, the image is always the same distance behind the mirror as the object is in front.

• Image Distance (di​) = 2.0 m.

Step 3: Calculate Total Distance

• Total Distance = do​+di​

• 2.0 m+2.0 m=4.0 meters.

Example 2:

You look at the reflection of a wall clock in a plane mirror. The image in the mirror clearly shows the time as 3:00. What is the actual real-time on the clock? 

The Concept: Lateral Inversion Plane mirrors reverse images from left to right.

• If the "virtual" hands are pointing to the Right (at the 3), the "real" hands must be pointing to the Left (at the 9).

Answer: The actual time is 9:00.

Example 3:

A ray of light hits a plane mirror at an angle of incidence of 35 ∘. What is the angle between the incident ray and the reflected ray? 

Step 1: Find the Angle of Reflection

• According to the Law of Reflection: θ i​ = θ r

• If θi​ = 35 ∘, then θr ​= 35 ∘.

Step 2: Add them together

• The question asks for the total angle between the two rays.

• Total Angle = θi ​+ θr​

• 35 ∘+35 ∘=70 ∘.