If an incident ray passes through the focus, the reflected ray will

Options

A. pass through the pole
B. retrace its path
C. be parallel to the principal axis
D. pass through the centre of curvature

Explanation

To solve the question, "If an incident ray passes through the focus, the reflected ray will," we can follow these steps:

### Step 1: Understand the Setup
We are dealing with a concave mirror where light rays interact with the mirror surface. The focus (F) is a point where parallel rays converge after reflection.

**Hint:** Remember that the focus is a key point in the behavior of light rays with mirrors.

### Step 2: Identify the Incident Ray
The incident ray in this case is defined as a ray that is passing through the focus of the mirror.

**Hint:** Visualize the path of the ray as it approaches the mirror.

### Step 3: Apply the Law of Reflection
According to the law of reflection, the angle of incidence (the angle between the incident ray and the normal to the mirror surface) is equal to the angle of reflection (the angle between the reflected ray and the normal).

**Hint:** Recall that the normal line is perpendicular to the surface of the mirror at the point of incidence.

### Step 4: Determine the Path of the Reflected Ray
When a ray passes through the focus and strikes the mirror, it will reflect off the mirror. Due to the properties of concave mirrors, a ray that comes from the focus will reflect off the mirror and travel parallel to the principal axis.

**Hint:** Think about how rays behave when they converge at the focus and how they reflect off the mirror.

### Step 5: Conclude the Reflection Behavior
Thus, the reflected ray will be parallel to the principal axis of the mirror.

**Hint:** Consider the principle of reversibility of light, which states that the path of light can be traced back in the same manner.

### Final Answer
The reflected ray will be parallel to the principal axis.