A periscope is used on a submarine - Leaving Cert Physics - Question 10 - 2021

1. The angle of incidence is equal to the angle of reflection (𝜃i = 𝜃r).
2. The incident ray, the reflected ray, and the normal to the surface all lie in the same plane.

Apparatus: Plane mirror, sheet of paper, raybox, protractor.

Procedure:

1. Place the plane mirror on a flat surface and shine a light ray from the raybox towards the mirror.
2. Draw the incident ray and the normal at the point of incidence.
3. Measure the angle of incidence, and then reflect the ray off the mirror and measure the angle of reflection.
4. Observe that the angle of incidence is equal to the angle of reflection, confirming the laws of reflection.

In the completed ray diagram, show the object, focal point (f), and the concave mirror. Include the following:

1. A ray parallel to the principal axis reflecting off the mirror and passing through the focal point.
2. A ray passing through the focal point reflecting parallel to the principal axis.
3. Mark the position of the real image where the two reflected rays converge.

Magnification (M) is calculated using the formula:
$M = \frac{h_{image}}{h_{object}} = \frac{3}{2} = 1.5$
This means the image is 1.5 times larger than the object.

Using the mirror formula: $\frac{1}{f} = \frac{1}{d_{object}} + \frac{1}{d_{image}}$
We know that:

• Focal length (f) can be calculated using the magnification formula
• The object distance (d_object) is 17 cm.
• Rearranging gives: $d_{image} = \frac{d_{object} \times f}{d_{object} - f}$
  Through calculations, the image distance can be found as 25.5 cm.

Concave mirrors are commonly used in reflecting telescopes because they can gather and focus light effectively, providing clearer images of distant celestial objects.

Convex mirrors are often used for security purposes, such as in stores and parking lots, to provide a wide field of view and reduce blind spots.