3.2.1 Reflection of light (3)
Resources |
Revision Questions |
Physics
Login to see all questions
Click on a question to view the answer
1.
A student shines a laser beam onto a plane mirror. The angle of incidence is measured to be 45°. Calculate the angle of reflection. Explain why this relationship is important in the design of optical instruments.
The angle of reflection is equal to the angle of incidence. Therefore, the angle of reflection is 45°. The relationship between the angle of incidence and the angle of reflection is fundamental to the design of many optical instruments.
Importance in optical instruments:
- Image Formation: Optical instruments like telescopes, microscopes, and cameras rely on the predictable reflection of light to form images. The consistent relationship between incidence and reflection ensures that light rays are directed in a controlled manner to create a clear and accurate image.
- Efficiency: By understanding and controlling the angle of incidence, designers can maximize the amount of light reflected, improving the efficiency of the instrument.
- Stability: The predictable nature of reflection contributes to the stability and reliability of optical instruments. Precise angles are crucial for maintaining the correct image formation.
2.
A student stands 1.5 m from a plane mirror. They move 0.5 m further away from the mirror. Calculate the change in the distance of the image from the mirror. Show your working.
Initial distance of student from mirror: 1.5 m
Final distance of student from mirror: 1.5 m + 0.5 m = 2.0 m
Distance of image from mirror when student is 1.5m away: 1.5 m
Distance of image from mirror when student is 2.0m away: 1.5 m
Change in distance of image from mirror: 1.5 m - 1.5 m = 0 m
Working: The distance of the image from the mirror remains the same as the distance of the object from the mirror for a plane mirror. Therefore, even though the student moves further away, the image remains at the same distance from the mirror.
3.
A plane mirror is placed 2.0 m from a wall. A student walks towards the mirror at a speed of 0.5 m/s. Draw a ray diagram to show the path of light from the student, reflecting off the mirror, and reaching a point on the wall directly opposite the mirror. State, with a reason, whether the image formed is real or virtual.
Diagram: A ray diagram should clearly show a ray of light originating from the student, traveling to the mirror, reflecting at the angle of incidence equal to the angle of reflection, and then traveling to a point on the wall directly opposite the mirror. The angle of incidence should be clearly marked and equal to the angle of reflection. The reflected ray should be shown extending back to the point on the wall.
Real or Virtual: The image formed is real. This is because the reflected rays of light actually converge at a point on the wall. A real image can be projected onto a screen.
Reason: The light rays from the student are reflected and converge at a point on the wall. This convergence of light rays indicates a real image formation.